An Open-Label Extension Study of Continuing Treatment With Trofinetide for Rett Syndrome
Phase: PHASE3
Conditions: Rett Syndrome
Sponsor: ACADIA Pharmaceuticals Inc.

Official Title: An Open-Label Extension Study of Continuing Treatment with 
Trofinetide for Rett Syndrome 
NCT Numbers: NCT04776746 
Document Date: 19 December 2022 

Study: ACP-2566-005 
 
Final Version: 1.0 
Clinical Study Protocol Amendment 1 
 
Date: 19 December 2022 
 
    Confidential and Proprietary Information of Acadia Pharmaceuticals Inc. 
Page 1 of 65 
 
 
 
 
CLINICAL STUDY PROTOCOL 
 
An Open-Label Extension Study of Continuing Treatment with Trofinetide 
for Rett Syndrome  
 
Protocol Number: ACP-2566-005 
Amendment 1 
 
Original Protocol Date: 11 September 2020 
Protocol Amendment 1 Date: 19 December 2022 
 
 
 
 
 
Confidentiality Statement 
This protocol is the confidential information of Acadia Pharmaceuticals Inc. and is intended solely for the 
guidance of the clinical investigation. This protocol may not be disclosed to parties not associated with the 
clinical investigation or used for any purpose without the prior written consent of Acadia Pharmaceuticals Inc. 

Study: ACP-2566-005 
 
Final Version: 1.0 
Clinical Study Protocol Amendment 1 
 
Date: 19 December 2022 
 
    Confidential and Proprietary Information of Acadia Pharmaceuticals Inc. 
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SPONSOR SIGNATURE PAGE 
Title: An Open-Label Extension Study of Continuing Treatment with Trofinetide for Rett 
Syndrome 
 
Acadia Head of Rare Disease and External 
Innovation: 
 
Senior Vice President 
Head of Rare Disease and External 
Innovation & Chief Scientific Officer 
Acadia Pharmaceuticals Inc. 
  
  
 
 
 
 
 
 
 
 
 
 
 
See appended electronic signature page 
 
Signature 
 
Date 
 
 
Acadia Study Lead: 
 
Vice President, Clinical Development 
Acadia Pharmaceuticals Inc. 
 
 
 
 
 
 
 
 
See appended electronic signature page 
 
 
Signature 
 
Date 

Signature Page for ACP-2566-005 Protocol Amendment 1
Signature Page for ACP-2566-005 Protocol Amendment 1
Approve
Approve

Study: ACP-2566-005 
 
Final Version: 1.0 
Clinical Study Protocol Amendment 1 
 
Date: 19 December 2022 
 
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DECLARATION OF INVESTIGATOR 
I confirm that I have read the above protocol. I understand it, and I will work according to the 
moral, ethical, and scientific principles governing clinical research as set out in the principles 
of Good Clinical Practice, as required by International Council for Harmonisation of 
Technical Requirements for Pharmaceuticals for Human Use (ICH) Guideline E6 and as 
described in the United States (US) Code of Federal Regulations (CFR) 21 CFR parts 50, 54, 
56, 312, and according to applicable local requirements. 
Confidentiality Statement 
The confidential information in this document is provided to you as an Investigator or 
Consultant for review by you, your staff, and the applicable institutional review board/ethics 
committee. Your acceptance of this document constitutes agreement that you will not disclose 
the information contained herein to others without written authorization from the Sponsor. 
Principal Investigator 
 
 
Signature 
 
Date 
 
 
 
Name (printed) 
 
 
 
 

Study: ACP-2566-005 
 
Final Version: 1.0 
Clinical Study Protocol Amendment 1 
 
Date: 19 December 2022 
 
    Confidential and Proprietary Information of Acadia Pharmaceuticals Inc. 
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PROTOCOL SYNOPSIS1 
Protocol 
Number 
ACP-2566-005 
EudraCT 
Number 
Not applicable 
Protocol Title 
An Open-Label Extension Study of Continuing Treatment with 
Trofinetide for Rett Syndrome 
Name of 
Investigational 
Product 
Trofinetide oral solution 
Indication 
Rett syndrome  
Phase of 
Development 
3 
Sponsor 
Acadia Pharmaceuticals Inc. 
 
 
Primary Objective 
• To investigate the safety and 
tolerability of continued long-term 
treatment with oral trofinetide in girls 
and women with Rett syndrome 
 
Primary Endpoints 
• Treatment-emergent adverse events 
(TEAEs) 
• Serious adverse events (SAEs) 
• Withdrawals due to adverse events (AEs) 
• Potentially clinically important changes in 
other safety assessments 
 
 
 
1 NOTE: In this protocol, as in FDA guidance documents, the use of the word ”should” means that something is 
suggested or recommended, but not required. If something “may be” done, the meaning is that something is 
allowed, but not required. The terms “must” and “will” mean that something is required. 

Study: ACP-2566-005 
 
Final Version: 1.0 
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Date: 19 December 2022 
 
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Exploratory Objectives 
• To investigate the efficacy of 
long-term treatment with oral 
trofinetide in girls and women with 
Rett syndrome 
 
 
 
• To investigate the efficacy of 
long-term treatment with oral 
trofinetide in girls and women with 
Rett syndrome on overall ability to 
communicate  
• To investigate the benefit of long-term 
treatment with oral trofinetide on 
overall quality of life for girls and 
women with Rett syndrome 
• To investigate the efficacy of 
long-term treatment with oral 
trofinetide in girls and women with 
Rett syndrome on: 
o Hand function 
o Ambulation and other gross 
motor skills 
o Ability to communicate 
choices and preferences 
o Ability to communicate 
verbally 
• To investigate the efficacy of 
long-term treatment with oral 
trofinetide on a global assessment of 
the severity of illness in girls and 
women with Rett syndrome 
• To investigate the benefit of long-term 
treatment with oral trofinetide on the 
burden on caregivers of girls and 
women with Rett syndrome 
• To investigate the benefit of long-term 
treatment with oral trofinetide on the 
Exploratory Endpoints 
• Rett Syndrome Behaviour Questionnaire 
(RSBQ) total score – change from Baseline 
to end of treatment visit 
• Clinical Global Impression–Improvement 
(CGI-I) Score at the Week 12 visit 
(assessing improvement from Baseline of 
the antecedent Study ACP-2566-004) 
Change from Baseline to end of treatment visit 
in: 
• Communication and Symbolic Behavior 
Scales-Developmental Profile™ 
Infant-Toddler Checklist – Social 
Composite Score (CSBS-DP-IT Social) 
• Overall Quality of Life Rating of the 
Impact of Childhood Neurologic Disability 
(ICND) Scale 
• Rett Syndrome Clinician Rating of Hand 
Function (RTT-HF) 
• Rett Syndrome Clinician Rating of 
Ambulation and Gross Motor Skills 
(RTT-AMB) 
• Rett Syndrome Clinician Rating of Ability 
to Communicate Choices (RTT-COMC) 
• Rett Syndrome Clinician Rating of Verbal 
Communication (RTT-VCOM) 
• Clinical Global Impression–Severity 
(CGI-S) 
• Rett Syndrome Caregiver Burden 
Inventory (RTT-CBI) Total Score (items 
1-24) 
 

Study: ACP-2566-005 
 
Final Version: 1.0 
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Date: 19 December 2022 
 
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impact of the disability on the child’s 
and family’s everyday life 
 
Number of Study 
Sites 
Approximately 28 sites will participate in this study. 
Number of 
Subjects Planned 
The sample size of this open-label study is not determined based on 
statistical considerations. However, subjects enrolled in the present 
study are those who have completed the antecedent study, 
ACP-2566-004, and rolled over to the present study. Since 
approximately 180 subjects are to be enrolled in the ACP-2566-004 
study and it is expected 85% of these subjects will complete Study 
ACP-2566-004 and rollover to the present study, the number of 
subjects in the present study will be approximately 153. 
Test Product, 
Dose, and 
Administration 
The subject’s assigned dose for this study will be the final dose from 
the antecedent study. 
If the subject’s weight at the Baseline visit of the present study or after 
52 weeks in the present study, or thereafter puts them in a new weight 
category, the Investigator may decide to increase the dose to the dose 
associated with the new weight category.  
Study drug is administered twice a day, once in the morning and once 
in the afternoon or evening. There should be at least 8 hours between 
doses. The study drug may be given with or without food.  
Doses may be taken orally or administered by gastrostomy (G) tube 
(doses administered via gastrojejunal [GJ] tubes must be administered 
through the G-port). 
If the subject cannot tolerate administration of the full assigned dose 
(for example, if the subject experiences diarrhea), the Investigator may 
instruct the caregiver to reduce study drug to a dose as low as 3 g 
(15 mL) BID. In addition, up to 4 doses (in total, consecutive or 
non-consecutive) may be held for this reason. 
Study Design 
This is a multi-center, open-label, long-term study of trofinetide to 
monitor the safety and efficacy of continuing trofinetide therapy for 
subjects who previously completed a Phase 3 trofinetide treatment 
study. Subjects who complete the preceding open-label study 
(ACP-2566-004) will be eligible to enroll in the present study. The 
duration of participation for individual study subjects will be 
approximately 32 months, or less than 32 months if: 1) trofinetide 
becomes commercially available for the treatment of Rett syndrome or 
2) if development of trofinetide for Rett syndrome is discontinued. The 
Sponsor may discontinue the study for any reason.  

Study: ACP-2566-005 
 
Final Version: 1.0 
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Date: 19 December 2022 
 
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Legally acceptable representatives (LARs)/subjects must be consented 
prior to the procedures being performed at the end of treatment (EOT) 
visit of the antecedent study. The EOT visit of the antecedent study 
will serve as the Baseline visit of the present study. The data gathered 
at the EOT visit of the antecedent study serves as the baseline data of 
the present study. The study will have two periods: 
• Treatment period: up to approximately 32 months   
• Safety follow-up period: 30 days 
Open-label Treatment Period 
Dosing is twice a day, once in the morning and once in the evening.  
In addition to the study drug dispensed at the Baseline visit, additional 
investigational product will be shipped directly to the subject. 
Confirmation of delivery to the subject will be made by a visiting 
nurse. Study drug shipment, return, and accountability will be 
performed in accordance with the drug distribution plan.  
Subjects will have assessments completed at Week 12, Week 52, 
Week 104, and Week 130. Assessments may be completed in the clinic 
or off-site at the discretion of the Principal Investigator. 
Safety Follow-up Period (30 [+4] Days) 
Subjects will receive a follow-up telephone or telemedicine call to 
assess safety 30 (+4) days after the last dose of study drug if they do 
not begin to take commercially marketed trofinetide within the 30 days 
after completing the study, or if they discontinue prematurely from the 
study. 
The study schematic is provided in Figure S–1. 
The schedule of assessments is provided in Table S–1. 
Study Duration 
The duration of the study will be up to approximately 32 months and 
there will be a safety follow-up period of 30 days after the EOT/early 
termination (ET) visit. 
The study completion date is defined as the date the final subject, 
across all sites, completes their final protocol-defined assessment (i.e., 
the final 30-day follow-up telephone call). 
Main Criteria for 
Inclusion and 
Exclusion 
To be eligible for this study, subjects must meet all of the inclusion 
criteria and none of the exclusion criteria. 
Inclusion Criteria: 
1. Informed consent prior to the conduct of any study procedures 
is required as follows: 

Study: ACP-2566-005 
 
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a. For subjects who are minors: written informed consent 
will be obtained from the legally acceptable 
representative (LAR). The subject should provide 
written or oral assent if deemed able by the 
Investigator. The process of obtaining informed 
consent will be conducted in accordance with 
institutional review board (IRB) or ethics committee 
(EC) policy and applicable local law. 
b. For subjects who are not minors: written informed 
consent will be obtained from the LAR or the subject if 
deemed able by the Investigator. If the subject is 
deemed not able to provide consent, the subject should 
provide written or oral assent if deemed able by the 
Investigator. The process of obtaining informed 
consent will be conducted in accordance with IRB or 
EC policy and applicable local law. 
c. The subject’s caregiver must also provide written 
informed consent regarding their participation in the 
study prior to participating in any study procedures. 
2. Has completed the EOT visit of the antecedent trofinetide 
Study ACP-2566-004 (i.e., has completed 40 weeks) 
3. May benefit from continued treatment with open-label 
trofinetide in the judgment of the Investigator 
4. Can still swallow the study medication provided as a liquid 
solution or can take it by gastrostomy tube 
5. The subject’s caregiver has sufficient language skills to 
complete the caregiver assessments  
Childbearing Potential 
6. Subjects of childbearing potential must abstain from sexual 
activity for the duration of the study and for at least 30 days 
thereafter. If a subject is sexually active or becomes sexually 
active during the study, she must use 2 clinically acceptable 
methods of contraception (e.g., oral, intrauterine device [IUD], 
diaphragm plus spermicide, injectable, transdermal or 
implantable contraception) for the duration of the study and for 
at least 30 days thereafter. Subject must not be pregnant or 
breastfeeding. 
 
Exclusion Criteria: 
1. Began treatment with growth hormone during the antecedent 
study  
2. Began treatment with IGF-1 during the antecedent study 

Study: ACP-2566-005 
 
Final Version: 1.0 
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3. Began treatment with insulin during the antecedent study  
4. Has developed a clinically significant cardiovascular, 
endocrine (such as hypo- or hyperthyroidism, Type 1 diabetes 
mellitus, or uncontrolled Type 2 diabetes mellitus), renal, 
hepatic, respiratory, or gastrointestinal disease (such as celiac 
disease or inflammatory bowel disease)  
5. Subject is judged by the Investigator or the Medical Monitor to 
be inappropriate for the study due to AEs, medical condition, 
or noncompliance with investigational product or study 
procedures in the antecedent study 
6. Has a clinically significant abnormality in vital signs at 
Baseline 
7. Has an average QTcF interval of >450 ms on the Baseline ECG 
performed before the first dose of trofinetide is given in the 
present study (i.e., the ECG performed at the EOT visit of the 
antecedent study) 
8. Has developed a clinically significant ECG finding during the 
antecedent study 
9. Is judged by the Investigator or the Medical Monitor to be 
inappropriate for the study for any reason 
Optional 
Caregiver 
Interview 
Participation of caregivers in an interview is an optional component of 
the study. Caregivers will be interviewed by a 3rd party central agency 
about the study subject’s and caregivers’ experience of treatment in 
trofinetide studies. Only caregivers who sign a separate informed 
consent will be interviewed. The results of caregiver interviews will be 
summarized. The caregiver interview will be administered at or before 
the final study visit (Week 130 [EOT/ET]). 
Sample Size 
Calculations 
Approximately 153 subjects will be enrolled in this study. The sample 
size is not based on statistical considerations but will depend on the 
number of subjects who transition into this open-label extension study 
from the antecedent study.   
Statistical 
Methods 
The purpose of this study is to collect safety data from subjects 
exposed to trofinetide in this study. Exploratory objectives include 
assessment of efficacy outcome measures over time. No formal testing 
of hypotheses is planned; all outcomes will be summarized 
descriptively. 
Analysis Sets 
The Safety Analysis Set will include all subjects who received at least 
one dose of study drug in this study. This analysis set will be used for 
all safety as well as any descriptive efficacy analyses. 

Study: ACP-2566-005 
 
Final Version: 1.0 
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Descriptive Statistics 
All endpoints will be summarized for the Safety Analysis Set. 
Data from the EOT visit procedures of Study ACP-2566-004 will be 
carried over as Baseline information in the present study, as applicable, 
except for CGI-I. 
Continuous measurement results will be reported using the number of 
subjects with data values, mean, standard error of the mean, median, 
standard deviation, minimum, and maximum. For each categorical 
outcome, the frequency and percentage of subjects in each category 
will be reported.  
Primary Analyses 
Adverse events will be classified into standard terminology using the 
Medical Dictionary for Regulatory Activities (MedDRA). All AEs will 
be listed and TEAEs will be summarized by system organ class and 
preferred term. A TEAE is defined as an AE that started after the first 
administration of study drug and no later than the last administration of 
study drug plus 30 days. Summaries by maximum severity and by 
relationship to study drug will also be provided. Serious TEAEs, fatal 
AEs, and TEAEs leading to discontinuation will also be summarized. 
Descriptive summary statistics for ECG, vital signs and body weight, 
and clinical laboratory parameters, including observed values and 
changes from Baseline, will be tabulated by timepoint. Additionally, 
categorical analyses will be conducted on the incidence of subjects 
with prolonged QTc intervals and changes in QTc intervals in 
accordance with International Council for Harmonisation (ICH) 
guidelines. 
Efficacy Analyses 
Descriptive summary statistics for RSBQ (absolute values and change 
from Baseline), CGI-I (absolute values, assessed by comparing to the 
status at Study ACP-2566-004 baseline), CGI-S, CSBS-DP-IT Social, 
each of the four Rett Syndrome Clinician Rating scales, RTT-CBI, and 
ICND Quality of Life score absolute values and change from Baseline 
will be summarized by timepoint.  
Date 
19 December 2022 

Study: ACP-2566-005 
 
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Date: 19 December 2022 
 
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Figure S–1 
Schematic of Study Design for ACP-2566-005 
 

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Table S–1 
Schedule of Events and Assessments for Study ACP-2566-005 
 
Period 
Baseline 
Open-label Treatment Period 
Safety  
Follow-up 
Visit Frequency  
 
Week 12 
Week 52 Week 104 
Week 
130/EOT/ET 
EOT/ET 
+30 
days 
Visit Number 
1 
2 
3 
4 
5 
 
Visit window (days) 
N/A 
±7 
±7 
±7 
+7 
+4 
Type of Visit a 
Clinic or Off-site 
Telephone or 
Telemedicine 
Informed consent 
Xb 
 
 
 
 
 
Inclusion/exclusion criteria 
X 
 
 
 
 
 
Physical examination a 
X 
X 
X 
X 
X 
 
Vital signs c 
X 
X 
X 
X 
X 
 
Height 
X 
X 
X 
X 
X 
 
Weight a 
Xa 
X 
X 
X 
X 
 
12-lead electrocardiogram (ECG) 
Xd 
X 
X 
X 
X 
 
Clinical laboratory tests (hematology, 
chemistry) 
X 
X 
X 
X 
X 
 
Urinalysis 
X 
X 
X 
X 
X 
 
Serum pregnancy teste 
X 
X 
X 
X 
X 
 
Rett Syndrome Behaviour 
Questionnaire (RSBQ) 
X 
X 
X 
X 
X 
 
Clinical Global Impression–
Improvement since Baseline of Study 
ACP-2566-004 (CGI-I) f 
X 
X 
 
 
 
 
Clinical Global Impression–Severity 
(CGI-S) 
X 
X 
X 
X 
X 
 
Communication and Symbolic 
Behavior Scales-Developmental 
Profile™ Infant-Toddler (CSBS-DP-
IT) Checklist 
X 
 
X 
X 
X 
 
Overall Quality of Life Rating of the 
Impact of Childhood Neurologic 
Disability (ICND) Scale 
X 
 
X 
X 
X 
 
Rett Syndrome Clinician Rating of 
Hand Function (RTT-HF) 
X 
X 
X 
X 
X 
 
Rett Syndrome Clinician Rating of 
Ambulation and Gross Motor Skills 
(RTT-AMB) 
X 
X 
X 
X 
X 
 
Rett Syndrome Clinician Rating of 
Ability to Communicate Choices 
(RTT-COMC) a 
X 
X 
X 
 
X 
 
Rett Syndrome Clinician Rating of 
Verbal Communication 
(RTT-VCOM) 
X 
X 
X 
 
X 
 
Rett Syndrome Caregiver Burden 
Inventory (RTT-CBI) 
X 
 
X 
 
X 
 
Table abbreviations and footnotes provided on next page 

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Table S–1 
Schedule of Events and Assessments for Study ACP-2566-005 
(Continued) 
Period 
Baseline 
Open-label Treatment Period 
Safety  
Follow-up 
Visit Frequency  
 
Week 12 
Week 52 
Week 104 
Week 
130/EOT/ET 
EOT/ET 
+30 
days 
Visit Number 
1 
2 
3 
4 
5 
 
Visit window (days) 
N/A 
±7 
±7 
±7 
+7 
+4 
Type of Visit a 
Clinic or Off-site 
Telephone or 
Telemedicine 
Dispensing and review of semi-
structured caregiver diary, 
including seizure diary 
X 
X 
X 
X 
X 
 
Concomitant medications 
X 
X 
X 
X 
X 
X 
Assessment of adverse events 
X 
X 
X 
X 
X 
X 
Optional caregiver interviewg 
 
X 
 
Study drug dispensed h 
X 
 
 
 
 
 
Authorization of study drug 
dispensation h 
X-------------------------------------------------X 
 
 
Study drug return h 
X-------------------------------------------------------------------X 
 
Study drug accountability h 
 
X 
X 
X 
X 
 
Abbreviations: EOT=end of treatment; ET=early termination 
a 
Assessments may be completed in the clinic or off-site, at the discretion of the Principal Investigator. When a study 
visit takes place off-site, the physical examination will not be required. Weight should be measured whenever possible 
at off-site visits. Measurement of weight is necessary at Baseline in order to determine the starting dose. The 
RTT-COMC should be completed if possible, but it is not required. 
b  
Consent for the present study must be obtained prior to performance of the EOT procedures at the EOT visit in the 
antecedent study. Data from the EOT visit procedures of the antecedent study will be carried over as Baseline 
information in the present study, as applicable.  
c  
Vital signs will include body temperature, resting respiration rate, sitting systolic and diastolic blood pressure, and 
pulse rate. The sitting blood pressure will be measured after the subject has been sitting for ≥3 minutes. 
d  
ECGs will be completed in triplicate at Visit 1 (Baseline) before dosing. The ECG taken at the EOT visit in the 
antecedent study is the Baseline ECG of the present study. A single ECG will be completed at all other designated 
visits.  
e  
For subjects who have reached menarche and have not had surgical sterilization 
f  
The CGI-I assessments for each post-Baseline visit will be assessing improvement from Baseline of the antecedent 
Study ACP-2566-004. 
g  
Caregiver interviews will be conducted remotely via telephone at or before the final study visit (Week 130 [EOT/ET]). 
Participation in the caregiver interview is an optional component of the study requiring a separate informed consent. 
h  
Investigational product will be shipped directly to the subject. Confirmation of delivery to the subject will be made by a 
visiting nurse. Study drug shipment, return, and accountability will be performed in accordance with the drug 
distribution plan. In addition, study drug will be dispensed at the site during the Baseline visit when the visit is 
conducted in the clinic. 

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TABLE OF CONTENTS 
SPONSOR SIGNATURE PAGE ............................................................................................... 2 
DECLARATION OF INVESTIGATOR ................................................................................... 4 
PROTOCOL SYNOPSIS ........................................................................................................... 5 
TABLE OF CONTENTS ......................................................................................................... 15 
LIST OF TABLES ................................................................................................................... 19 
LIST OF FIGURES ................................................................................................................. 19 
LIST OF ABBREVIATIONS AND DEFINITION OF TERMS ............................................. 20 
1 
INTRODUCTION ...................................................................................................... 22 
1.1 
Background Information ............................................................................................ 22 
1.2 
Investigational Product ............................................................................................... 23 
1.3 
Previous Clinical Experience ..................................................................................... 24 
1.4 
Study Rationale .......................................................................................................... 27 
2 
STUDY OBJECTIVES AND ENDPOINTS .............................................................. 28 
2.1 
Primary Objective....................................................................................................... 28 
2.1.1 
Primary Endpoints ...................................................................................................... 28 
2.2 
Exploratory Objectives ............................................................................................... 28 
2.2.1 
Exploratory Endpoints ................................................................................................ 29 
3 
STUDY DESCRIPTION ............................................................................................ 29 
3.1 
Overview of Study Design ......................................................................................... 29 
3.1.1 
Open-label Treatment Period...................................................................................... 30 
3.1.2 
Safety Follow-Up Period (30 [+4] Days) ................................................................... 31 
4 
SUBJECT ELIGIBILITY AND WITHDRAWAL CRITERIA .................................. 31 
4.1 
Inclusion Criteria ........................................................................................................ 31 
4.2 
Exclusion Criteria ....................................................................................................... 32 
4.3 
Subject Withdrawal of Consent .................................................................................. 32 
4.4 
Subject or Study Discontinuation ............................................................................... 33 
4.4.1 
Post-Baseline QTcF Interval Stopping Criteria .......................................................... 33 
4.4.2 
Handling of Subject Discontinuation During the Treatment Period .......................... 34 
4.5 
Subject Lost to Follow-Up ......................................................................................... 34 
4.6 
Concomitant Therapy ................................................................................................. 34 

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4.6.1 
Permitted and Prohibited Medications ....................................................................... 35 
5 
INVESTIGATIONAL PRODUCT ............................................................................. 35 
5.1 
Investigational Product Description ........................................................................... 35 
5.1.1 
Formulation, Appearance, and Packaging .................................................................. 35 
5.1.2 
Product Storage and Stability ..................................................................................... 36 
5.1.3 
Dosing and Administration ......................................................................................... 36 
5.1.3.1 Dosing ........................................................................................................................ 36 
5.1.3.2 Administration of Study Drug .................................................................................... 37 
5.1.4 
Method of Assigning Subjects to Treatment Groups.................................................. 37 
5.1.5 
Blinding ...................................................................................................................... 37 
5.1.6 
Study Drug Compliance ............................................................................................. 37 
5.1.7 
Overdose ..................................................................................................................... 37 
5.2 
Investigational Product Accountability Procedures ................................................... 37 
6 
STUDY PROCEDURES ............................................................................................ 38 
6.1 
Efficacy Assessments ................................................................................................. 38 
6.1.1 
Rett Syndrome Behaviour Questionnaire (RSBQ) ..................................................... 38 
6.1.2 
Clinical Global Impression–Improvement (CGI-I) and Clinical Global Impression–
Severity (CGI-S)......................................................................................................... 39 
6.1.3 
Communication and Symbolic Behavior Scales - Developmental Profile Infant-
Toddler (CSBS-DP-IT) Checklist .............................................................................. 40 
6.1.4 
The Quality of Life Rating of the Impact of Childhood Neurologic Disability (ICND) 
Scale ........................................................................................................................... 41 
6.1.5 
Rett Syndrome Clinician Rating of Hand Function (RTT-HF) .................................. 41 
6.1.6 
Rett Syndrome Clinician Rating of Ambulation and Gross Motor Skills (RTT-AMB)
 .................................................................................................................................... 41 
6.1.7 
Rett Syndrome Clinician Rating of Ability to Communicate Choices (RTT-COMC)
 .................................................................................................................................... 42 
6.1.8 
Rett Syndrome Clinician Rating of Verbal Communication (RTT-VCOM) .............. 42 
6.1.9 
Rett Syndrome Caregiver Burden Inventory (RTT-CBI) ........................................... 42 
6.2 
Safety Assessments..................................................................................................... 43 
6.2.1 
Physical Examination ................................................................................................. 43 
6.2.2 
Vital Signs .................................................................................................................. 43 
6.2.3 
Height, Weight, and Body Mass Index ....................................................................... 43 
6.2.4 
Electrocardiograms ..................................................................................................... 43 
6.2.4.1 Post-Enrollment QTcF Interval Stopping Criteria ...................................................... 44 
6.2.5 
Laboratory Evaluations .............................................................................................. 44 
6.3 
Caregiver Diary .......................................................................................................... 45 
6.4 
Caregiver Interview .................................................................................................... 45 

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Date: 19 December 2022 
 
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7 
ADVERSE EVENTS ................................................................................................. 46 
7.1 
Specification of Safety Parameters............................................................................. 46 
7.1.1 
Definition of Adverse Event ....................................................................................... 46 
7.1.2 
Definition of Serious Adverse Event .......................................................................... 47 
7.2 
Classification of an Adverse Event ............................................................................ 48 
7.2.1 
Severity of Event ........................................................................................................ 48 
7.2.2 
Relationship to Study Drug ........................................................................................ 48 
7.2.3 
Duration ...................................................................................................................... 49 
7.2.4 
Frequency ................................................................................................................... 49 
7.2.5 
Action Taken with Study Drug ................................................................................... 49 
7.2.6 
Therapy ....................................................................................................................... 49 
7.2.7 
Outcome ..................................................................................................................... 50 
7.2.8 
Seriousness ................................................................................................................. 50 
7.2.9 
Definition of Unexpectedness .................................................................................... 50 
7.3 
Time Period and Frequency for Event Assessment and Follow-Up ........................... 50 
7.4 
Reporting Procedures ................................................................................................. 51 
7.4.1 
Adverse Event Reporting ........................................................................................... 51 
7.4.2 
Serious Adverse Event Reporting............................................................................... 51 
7.4.3 
Reporting of Pregnancy .............................................................................................. 52 
7.4.4 
Reporting of Overdose ............................................................................................... 52 
8 
CLINICAL MONITORING ....................................................................................... 53 
9 
STATISTICAL METHODS AND DATA ANALYSIS .............................................. 53 
9.1 
Statistical and Analytical Plans .................................................................................. 53 
9.2 
Statistical Hypotheses................................................................................................. 53 
9.3 
Sample Size Determination ........................................................................................ 53 
9.4 
Subject Populations for Analysis ................................................................................ 53 
9.5 
Statistical Analyses ..................................................................................................... 53 
9.5.1 
General Approach ....................................................................................................... 53 
9.5.2 
Primary Analyses ........................................................................................................ 54 
9.5.3 
Efficacy Analyses ....................................................................................................... 54 
9.5.4 
Subgroup Analyses ..................................................................................................... 54 
9.6 
Interim Analyses ......................................................................................................... 54 
9.7 
Measures to Minimize Bias ........................................................................................ 54 
9.8 
Breaking the Study Blind/Subject Code ..................................................................... 54 
10 
STUDY MANAGEMENT AND DATA COLLECTION .......................................... 55 

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10.1 
Data Collection and Management Responsibilities.................................................... 55 
10.2 
Source Documents ...................................................................................................... 55 
10.3 
Case Report Forms ..................................................................................................... 55 
10.4 
Confidentiality ............................................................................................................ 55 
10.5 
Study Records Retention ............................................................................................ 56 
10.6 
Protocol Exceptions and Deviations........................................................................... 56 
10.7 
Protocol Amendments ................................................................................................ 56 
11 
QUALITY MANAGEMENT .................................................................................... 57 
11.1 
Risk Management ....................................................................................................... 57 
11.2 
Quality Control and Quality Assurance...................................................................... 57 
12 
ETHICAL CONSIDERATIONS ................................................................................ 58 
12.1 
Ethical Standard ......................................................................................................... 58 
12.2 
Institutional Review Board/Ethics Committee ........................................................... 58 
12.3 
Informed Consent Process .......................................................................................... 59 
12.3.1 Consent and Other Informational Documents Provided to Subjects .......................... 60 
12.3.2 Consent Procedures and Documentation .................................................................... 60 
13 
PUBLICATION PLAN .............................................................................................. 61 
14 
CONFLICT OF INTEREST POLICY ....................................................................... 61 
14.1 
Finance, Insurance, and Indemnity............................................................................. 61 
15 
LITERATURE REFERENCES .................................................................................. 62 
 

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LIST OF TABLES 
Table S–1 
Schedule of Events and Assessments for Study ACP-2566-005 ..................... 13 
Table 1–1 
Change from Treatment Baseline (Day 14) to End of Treatment (Day 54) 
in Core Efficacy Outcomes (mITT) (Neu-2566-RETT-002) ........................... 25 
Table 5–1 
Weight-Dosing Categories ............................................................................... 36 
 
LIST OF FIGURES 
Figure S–1 
Schematic of Study Design for ACP-2566-005 ............................................... 12 
Figure 1–1 
Comparison of Change from Treatment Baseline on the RSBQ at 
Follow-Up Assessments Between 200 mg/kg BID and Placebo BID 
Treatment Groups ............................................................................................ 26 
 

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LIST OF ABBREVIATIONS AND DEFINITION OF TERMS 
Term 
Definition 
AE 
adverse event(s) 
AUC0-12ss 
area under the blood concentration-time curve from 0 to 12 hours 
BID 
twice daily 
CFR 
Code of Federal Regulations 
CGI-I 
Clinical Global Impression–Improvement 
CGI-S 
Clinical Global Impression–Severity 
Cmax 
maximum observed drug concentration 
CSBS-DP-IT 
Communication and Symbolic Behavior Scales-Developmental 
Profile™ Infant-Toddler Checklist 
EC 
ethics committee 
ECG 
electrocardiogram 
eCRF 
electronic case report form 
EOT 
end of treatment 
ET 
early termination 
EU GDPR 
European Union General Data Protection Regulation 
GCP 
Good Clinical Practice 
GJ 
gastrojejunal 
GPE 
glycine-proline-glutamate 
ICF 
informed consent form 
ICH 
International Council for Harmonisation  
ICND 
Impact of Childhood Neurologic Disability Scale 
IGF-1 
insulin-like growth factor 1 
IRB 
institutional review board 
LAR 
legally acceptable representative 
MeCP2 
methyl-CpG binding protein 2  
MeCP2 
gene encoding methyl-CpG binding protein 2 (in animals) 
MECP2 
gene encoding methyl-CpG binding protein 2 (in humans) 
PK 
pharmacokinetic 
PR interval 
PR interval of ECG 
QRS interval 
QRS interval of ECG 
QT interval 
QT interval for heart rate of ECG 
QTc 
corrected QT interval of ECG for heart rate 
QTcB 
corrected QT interval using Bazett’s correction method 
QTcF 
corrected QT interval using Fridericia’s correction method 
RSBQ 
Rett Syndrome Behaviour Questionnaire 

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Term 
Definition 
RTT 
Rett syndrome 
RTT-AMB 
Rett Syndrome Clinician Rating of Ambulation and Gross Motor 
Skills 
RTT-CBI 
Rett Syndrome Caregiver Burden Inventory 
RTT-COMC 
Rett Syndrome Clinician Rating of Ability to Communicate 
Choices 
RTT-DSC 
RTT Domain Specific Visual Analog Scale 
RTT-HF 
Rett Syndrome Clinician Rating of Hand Function 
RTT-VCOM 
Rett Syndrome Clinician Rating of Verbal Communication 
SAE 
serious adverse event(s) 
TEAE 
treatment emergent adverse event(s) 
US 
United States 
 

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1 INTRODUCTION 
This document is a research protocol and the described study will be conducted in 
compliance with the protocol and the International Council for Harmonisation (ICH) Good 
Clinical Practice (GCP) Guideline.  
1.1 
Background Information 
Rett syndrome (RTT) is a seriously debilitating neurodevelopmental disorder for which there 
is currently no approved treatment. Its prevalence is reported as 1 in 10,000-15,000 female 
live births (Bienvenu et al. 2006; Neul et al. 2010). While the great majority of patients with 
RTT are females, males who meet the criteria for RTT have also been identified 
(Neul et al. 2019). In 96-98% of patients diagnosed with classic RTT, the disease is caused by 
mutations in the X-linked MECP2 gene (Percy et al. 2018). MECP2 encodes methyl-CpG 
binding protein 2 (MeCP2) which modulates gene expression by binding to methylated CpG 
dinucleotides, primarily by activating but also by repressing transcription (Ip et al. 2018; 
Neul et al. 2008; Kriaucionis and Bird 2003; Hite et al. 2009). The activity of the MeCP2 
protein is diminished in both neurons and astrocytes (Yasui et al. 2013). 
In patients with typical RTT, there is seemingly normal psychomotor development for the 
first 6 months of life, but soon thereafter the failure to reach normal developmental 
milestones is observed, followed by a period of developmental regression in which there is a 
loss of normal use of the hands and of spoken language (Samaco and Neul 2011). The period 
of developmental regression is accompanied by transient autistic features in many but not all 
individuals with RTT (Lee et al. 2013; Neul et al. 2014). Loss of social skills appears to 
stabilize or reverse after the regression period, and individuals with RTT demonstrate social 
intentions through eye contact (Young et al. 2008; Djukic and McDermott 2012; 
Urbanowicz et al. 2016). Nonetheless, social interaction and communication remain limited 
(Mount et al. 2003; Urbanowicz et al. 2015; Rose et al. 2013; Kaufmann et al. 2012; 
Woodyatt and Ozanne 1993). The intellectual disability in RTT appears to be profound; 
however, precise measurement of the extent of cognitive impairment is difficult because of 
the severe communication and motor deficits affecting most individuals 
(Byiers and Symons 2012; Clarkson et al. 2017). 
Seizures are common, although not diagnostic. Commonly observed symptoms include 
awake breathing disruptions, scoliosis, and interest in social interaction (intense eye 
communication) (Neul et al. 2010; Percy et al. 2010). Gastrointestinal symptoms, including 
constipation and chewing and swallowing difficulties, are observed in the majority of patients 
with RTT (Motil et al. 2012). Sudden changes in mood, screaming and inconsolable crying 
are common behaviors in children and adolescents with RTT (Mount et al. 2001, 2002; 
Robertson et al. 2006; Cianfaglione et al. 2015). These impairments can further exacerbate 

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other symptoms and disrupt activities of daily living including educational, recreational and 
treatment opportunities (Epstein et al. 2016; Perry et al. 1991; Thompson and Iwata 2001; 
Iemmi et al. 2016). Autonomic manifestations, which include abnormalities in cardiac and 
respiratory function, as well as in peripheral circulation, are considered to be predominantly 
of central nervous system origin. Rett syndrome is also characterized by impaired growth 
affecting the brain and other organ systems.  
Loss of purposeful hand use is a defining aspect of RTT during the onset of regression and at 
least 30% of individuals remain without any type of purposeful hand use (Downs et al. 2010). 
Individuals with some purposeful hand movements vary in their level of ability to reach for 
and grasp objects. The ability to self-feed is observed in 25-43% (Cass et al. 2003; 
Larsson et al. 2005; Downs et al. 2011). Poorer levels of hand function are associated with 
both age and severity of mobility impairment (Downs et al. 2011). 
In adulthood, a late motor deterioration stage occurs, characterized by worsening dystonia, 
rigidity, and in some cases deterioration in the ability to walk and parkinsonian symptoms. 
Affected individuals have a yearly death rate between 1% and 2%, with 25% of all deaths 
characterized as sudden and unexpected (Kerr et al. 1997; Samaco and Neul 2011). Women 
with RTT can survive into their fifties and occasionally longer (Samaco and Neul 2011). 
There are no medicines approved for the treatment of RTT. Treatment focuses on the 
management of each patient’s symptoms and, even in that regard, is often unsatisfactory and 
has only a limited effect on functional improvement. Accordingly, the burden on families and 
other caregivers is very great (Palacios-Ceña et al. 2018). 
1.2 
Investigational Product 
Trofinetide is a synthetic analog of glycine-proline-glutamate (also known as glypromate or 
GPE), a peptide that occurs naturally in the brain. GPE is the N-terminal tripeptide of the 
insulin-like growth factor 1 (IGF-1) protein. Trofinetide crosses the blood-brain barrier 
following oral administration. In the brain, it is believed to normalize decreased 
bioavailability of IGF-1 and GPE, as well as having an anti-inflammatory effect on 
pathologically activated glial cells. Both conditions contribute to deficits in synaptic 
development and functional maturation of synaptic plasticity that are fundamental to the 
wide-ranging effects of RTT. Tropea et al. (2009) observed that treatment with GPE reversed 
Rett-like symptoms in MeCP2 mutant mice. Therefore, the aim of treatment with trofinetide 
is to exert an effect on brain structure and function such as dendritic length and branching 
and long-term potentiation, which would be expected to lead to improvements across a wide 
range of symptoms of RTT. 

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1.3 
Previous Clinical Experience 
Trofinetide showed linear pharmacokinetics (PK) across the dose range tested in pediatric 
RTT patients. These PK results are in agreement with the data obtained previously in healthy 
subjects and in adult RTT patients. From a drug metabolism perspective, there was no 
accumulation, metabolic inhibition, or induction observed during treatment. For subjects 
treated with 50 mg/kg twice daily (BID), median maximum (peak) observed drug 
concentration (Cmax) was 17.7 μg/mL and median AUC0-12ss was 139.4 µg/mL·h. For subjects 
treated with 100 mg/kg BID, median Cmax was 52.6 μg/mL and median AUC0-12ss was 
338.6 µg/mL·h. For subjects treated with 200 mg/kg BID, median Cmax was 82.2 μg/mL and 
median AUC0-12ss was 505.1 µg/mL·h. The geometric mean of the apparent terminal 
elimination half-life (t1/2) varied from 5.3 h to 6.1 h across the three dosing groups. 
Trofinetide has exhibited a favorable safety and tolerability profile in two studies in subjects 
with Rett syndrome. Study Neu-2566-Rett-001 (NCT01703533) was a Phase 2 study of 
trofinetide in 56 adolescent and adult females with RTT (Glaze et al. 2017). Subjects were 
randomized 2:1 to 35 mg/kg trofinetide BID or placebo for 14 or 28 days (Cohorts 0 and 1, 
respectively) or 70 mg/kg trofinetide BID or placebo for 28 days (Cohort 2). Both dose levels 
were well-tolerated in this study, and no time- or dose-dependent adverse events (AEs) were 
apparent. The most common AE across all treatment groups was diarrhea (39% in the 
combined 35 mg/kg BID group, 11% in the 70 mg/kg BID group and 15% in the placebo 
group). The most common AE in the 70 mg/kg BID group was somnolence (17%; vs. 5% in 
the placebo group and 0% in the 35 mg/kg BID group). Four serious adverse events (SAEs) 
involving three subjects were reported during the study. In each of these instances, the AEs 
were deemed unrelated to the study medication. One subject withdrew from the study due to 
these events while the two subjects had already finished the study medication when their 
SAEs occurred. Each of these SAEs was deemed to be resolved by study conclusion. The 
results of this study also provided preliminary evidence of a treatment effect in the 70 mg/kg 
BID treatment group. 
A second Phase 2 study of oral trofinetide in pediatric and adolescent females with RTT, 
Study Neu-2566-RETT-002, assessed three dose levels of trofinetide (50 mg/kg BID, 
100 mg/kg BID, and 200 mg/kg BID vs. placebo) (Glaze et al. 2019). The study population 
consisted of female subjects between 5 and 15 years of age with a diagnosis of RTT and a 
proven mutation of the MECP2 gene. The primary analysis of efficacy was change from 
treatment Baseline (Visit 3, Day 14, end of placebo run-in) to End-of-Assessment (Visit 7, 
Day 54) between placebo and the 200 mg/kg BID treatment groups.  
At the time the study was initiated, there was no consensus upon the most appropriate and 
sensitive endpoint(s) for detecting beneficial drug effect in RTT, so the study examined five 

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unranked core efficacy outcome measures. Each of these five endpoints represented a 
different dimension or manifestation of the pathophysiology and clinical impairment directly 
associated with RTT. As shown below in Table 1–1, three of the five core endpoints showed a 
statistically significant difference from placebo at p<0.05 for the 200 mg/kg BID dose group: 
two clinician completed assessments (RTT Domain Specific Visual Analog Scale [RTT-DSC] 
and Clinical Global Impression–Improvement [CGI-I]) and one of the caregiver completed 
assessments (RSBQ). The remaining two primary endpoints were directionally positive. 
Table 1–1 
Change from Treatment Baseline (Day 14) to End of Treatment 
(Day 54) in Core Efficacy Outcomes (mITT) 
(Neu-2566-RETT-002) 
Outcome Measure 
Prespecified 
covariates 
p≤0.1 
Placebo 
(n=24) 
50 mg/kg 
(n=15) 
100 mg/kg 
(n=16) 
200 mg/kg 
(n=27) 
RSBQ Total 
D14 Treatment Baseline 
Change D14-D54 (LS mean) 
p-value vs. placeboa  
PR 
 
39.5 
-2.3 
 
 
44.7 
-3.0 
0.768 
 
40.3 
-1.5 
0.749 
 
42.2 
-6.7 
0.042 
RTT-DSC Total 
Exact Median Test 
D14 Treatment Baseline 
Change D14-D54 
p-value vs. placeboa 
UnAdj 
 
473.3 
-25.85 
 
 
450.0 
-32.50 
0.999 
 
445.3 
-12.10 
0.748 
 
516.6 
-76.00 
0.025 
CGI-I 
D14 Treatment Baseline 
Change D14-D54 (LS mean) 
p-value vs. placebob 
UnAdj 
 
(4) 
3.5 
 
 
(4) 
3.3 
0.391 
 
(4) 
3.4 
0.703 
 
(4) 
3.0 
0.029 
Top 3 Caregiver Concerns 
D14 Treatment Baseline 
Change D14-D54 (LS mean) 
p-value vs. placeboa 
UnAdj 
 
223.8 
-12.52 
 
 
237.6 
-16.56 
0.776 
 
211.5 
-2.09 
0.455 
 
245.9 
-18.54 
0.619 
MBA Total 
D14 Treatment Baseline 
Change D14-D54 (LS mean) 
p-value vs placeboa 
TBL, PR 
 
48.8 
-2.6 
 
 
46.6 
-2.8 
0.872 
 
48.6 
-2.4 
0.925 
 
46.6 
-2.9 
0.840 
Abbreviations: CGI-I=Clinical Global Impression–Improvement; LS =least squares; MBA=Motor Behavior 
Assessment; mITT=modified Intent-to-treat; PR=placebo response; RSBQ=Rett Syndrome Behaviour 
Questionaire; RTT-DSC=RTT Domain Specific Visual Analog Scale; TBL=treatment Baseline; 
UnAdj=unadjusted 
a 
Prespecified model covariates if p≤0.1: TBL and/or PR.  
b 
CGI-I has no pretreatment baseline value. The CGI-I values at Day 14 are the ratings of change from Day 0 
(the pretreatment Baseline) to Day 14 (end of placebo run-in). 
 
Among the three outcome measures that exhibited improvement compared to placebo for the 
200 mg/kg BID group, the median magnitude of effect (change) was 15% for RTT-DSC 
(vs. 5% for placebo) and the mean magnitude of effect (change) was 16% for RSBQ (vs. 6% 

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for placebo). For the CGI-I, the mean outcome was 3.0 for the 200 mg/kg BID group and was 
3.5 for placebo. For the CGI-I, more than 20% of subjects in the 200 mg/kg BID group were 
judged by clinicians to be “much improved”, compared with less than 5% of those on 
placebo. 
At the end of the dosing period, data indicate that clinical benefit (change from treatment 
Baseline) was continuing to accrue and that there was a divergent trend between the placebo 
and 200 mg/kg BID groups as highlighted below in Figure 1–1 for the RSBQ. Further, there 
is evidence of a significant diminution of effect following cessation of dosing, suggesting that 
the separation during the dosing period was due to beneficial treatment effect and not from 
other differences between the two arms that occurred simply by chance.  
Figure 1–1 
Comparison of Change from Treatment Baseline on the RSBQ at 
Follow-Up Assessments Between 200 mg/kg BID and Placebo BID 
Treatment Groups 
 
Abbreviations: BID=twice daily; LS=least squares; RSBQ=Rett Syndrome Behaviour Questionaire 
Note: End of treatment assessment is at Day 54. Treatment baseline is at Day 14, at the end of the placebo 
run-in. Day 66 is post-treatment. 
 
Trofinetide was generally safe and well tolerated. Most AEs reported during the double-blind 
treatment period were mild in intensity and the majority of events were deemed not related to 
study medication. The most common AEs reported from the start of the double-blind period 
across all treatment groups were diarrhea (27%), vomiting (15%), upper respiratory tract 
pyrexia (13%), and infection (12%). The most common AE from the start of the double-blind 
treatment period in the trofinetide treatment groups was diarrhea (27% in the 50 mg/kg BID 
group, 13% in the 100 mg/kg BID group, and 56% in the 200 mg/kg BID group compared 

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with 4% in the placebo group). The diarrhea associated with trofinetide may have been due to 
an improvement in gastrointestinal motility added to ongoing treatment with laxatives. Only 
three subjects experienced SAEs: one subject in the placebo BID group had an SAE of 
pneumonia, one subject in the 100 mg/kg BID group had an SAE of worsening of tonic 
cluster seizures, and one subject in the 200 mg/kg BID group had SAEs of streptococcal 
infection and pneumonia. In each of these instances, the SAEs were deemed not related to 
study medication and resolved by the end of the study. 
No changes in QTc interval attributable to treatment were seen in adolescent and adult 
subjects with RTT in study Neu-2566-RETT-001, nor in pediatric subjects in 
Neu-2566-Rett-002.   
Phase 2 studies of the oral formulation of trofinetide in adolescent and adult subjects with 
fragile X syndrome and of the intravenous formulation in adult subjects with moderate to 
severe traumatic brain injury (TBI) have also been completed and are described in the 
Investigator’s brochure. 
Always refer to the latest version of the trofinetide Investigator’s Brochure for the overall 
benefit/risk assessment and the most accurate and current information regarding drug 
metabolism, PK, efficacy, and safety. 
1.4 
Study Rationale 
As described above, Rett syndrome is a devastating disorder for which there is as yet no 
treatment beyond symptomatic care resulting in a great unmet medical need. In the two 
studies of trofinetide in girls and women with RTT, trofinetide has been well tolerated. The 
highest dose assessed, 200 mg/kg BID, was observed to provide benefit compared to placebo 
even in a relatively small study, as described above. The Acadia-sponsored Study 
ACP-2566-003 is a 12-week, placebo-controlled study of the efficacy and safety of treatment 
with trofinetide for Rett syndrome. Subjects who complete study ACP-2566-003 may be 
eligible to enter Study ACP-2566-004, a 40-week, open-label study of trofinetide. 
Some subjects will complete subject Study ACP-2566-004 before the earliest possible time at 
which trofinetide could become commercially available. The present study is an open-label 
study giving subjects who have completed ACP-2566-004 the opportunity to continue to 
receive open-label treatment with trofinetide until it becomes commercially available in the 
US. It is estimated that a 30-month study will provide enough time after the first subject 
completes Study ACP-2566-004 until trofinetide is available, or until it becomes apparent 
that trofinetide will not be marketed in the US. 

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2 STUDY OBJECTIVES AND ENDPOINTS 
2.1 
Primary Objective 
The primary objective of this study is to investigate the safety and tolerability of continued 
long-term treatment with oral trofinetide in girls and women with Rett syndrome. 
2.1.1 
Primary Endpoints 
The primary endpoints are:  
• Treatment-emergent adverse events (TEAEs) 
• Serious adverse events (SAEs)  
• Withdrawals due to AEs 
• Potentially clinically important changes in other safety assessments 
2.2 
Exploratory Objectives 
The exploratory objectives are:  
• To investigate the efficacy of long-term treatment with oral trofinetide in girls and 
women with Rett syndrome. 
• To investigate the efficacy of long-term treatment with oral trofinetide in girls and 
women with Rett syndrome on overall ability to communicate 
• To investigate the benefit of long-term treatment with oral trofinetide on overall 
quality of life for girls and women with Rett syndrome 
• To investigate the efficacy of long-term treatment with oral trofinetide in girls and 
women with Rett syndrome on: 
o Hand function  
o Ambulation and other gross motor skills  
o Ability to communicate choices and preferences 
o Ability to communicate verbally  
• To investigate the efficacy of long-term treatment with oral trofinetide on a global 
assessment of the severity of illness in girls and women with Rett syndrome 
• To investigate the benefit of long-term treatment with oral trofinetide on the burden 
on caregivers of girls and women with Rett syndrome 
• To investigate the benefit of long-term treatment with oral trofinetide on the impact of 
the disability on the child’s and family’s everyday life 

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2.2.1 
Exploratory Endpoints 
The exploratory endpoints for this study are: 
• Rett Syndrome Behaviour Questionnaire (RSBQ) total score – change from Baseline 
to end of treatment visit 
• Clinical Global Impression–Improvement (CGI-I) Score at the Week 12 visit 
(assessing improvement from Baseline of the antecedent Study ACP-2566-004)  
Change from Baseline to end of treatment visit in: 
• Communication and Symbolic Behavior Scales-Developmental Profile™ 
Infant-Toddler Checklist – Social Composite Score (CSBS-DP-IT Social)  
• Overall Quality of Life Rating of the Impact of Childhood Neurologic Disability 
(ICND) Scale 
• Rett Syndrome Clinician Rating of Hand Function (RTT-HF) 
• Rett Syndrome Clinician Rating of Ambulation and Gross Motor Skills (RTT-AMB) 
• Rett Syndrome Clinician Rating of Ability to Communicate Choices (RTT-COMC) 
• Rett Syndrome Clinician Rating of Verbal Communication (RTT-VCOM) 
• Clinical Global Impression–Severity (CGI-S) 
• Rett Syndrome Caregiver Burden Inventory (RTT-CBI) Total Score (items 1-24) 
 
3 STUDY DESCRIPTION 
3.1 
Overview of Study Design 
This is a multi-center, open-label, long-term study of trofinetide to monitor the safety and 
efficacy of continuing trofinetide therapy for subjects who previously completed a Phase 3 
trofinetide treatment study. Subjects who complete the preceding open-label study 
(ACP-2566-004) will be eligible to enroll in the present study.  
The duration of participation for individual study subjects will be approximately 32 months, 
or less than 32 months if: 1) trofinetide becomes commercially available for the treatment of 
Rett syndrome or 2) if development of trofinetide for Rett syndrome is discontinued. The 
Sponsor may discontinue the study for any reason. Note that not all subjects entering the 
present study will be treated for 32 months. It is anticipated that the time from which the first 
subject enters the present study until the predicted time that trofinetide receives marketing 
authorization and is marketed will be 29 months. Therefore, subjects who enter the present 

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study, for example, 6 months after the first subject enters, will receive treatment with 
trofinetide for approximately 23 months before the study is terminated based on the 
anticipated date of commercial availability of trofinetide. 
Legally acceptable representatives (LARs)/subjects must be consented prior to the 
procedures being performed at the end of treatment (EOT) visit of the antecedent study. The 
EOT visit of the antecedent study will serve as the Baseline visit of the present study. The 
data gathered at the EOT visit of the antecedent study serves as the baseline data of the 
present study.  
The duration of participation for individual study subjects will be up to approximately 
32 months with a safety follow-up period of 30 (+4) days. Approximately 28 sites will 
participate in this study. 
The study will have two periods (Figure S–1): 
• Treatment period: up to approximately 32 months  
• Safety follow-up period: 30 days 
The schedule of events and assessments is provided in Table S–1. As shown in the schedule 
of events, study visits may be done off-site rather than in the clinic, where appropriate and 
applicable. 
The study completion date is defined as the date the final subject, across all sites, completes 
their final protocol-defined assessment. An individual subject is considered to have 
completed the study on the date of her final protocol-defined assessment. Please note that the 
“final protocol-defined assessment” includes the follow-up visit or contact, whichever is 
later. Procedures for when a subject is lost to follow-up are provided in Section 4.5. 
3.1.1 
Open-label Treatment Period 
The EOT visit of the antecedent trofinetide study (e.g., ACP-2566-004) serves as the Baseline 
visit (Visit 1) of the present study. The day the first dose is taken will be considered Day 1 of 
dosing. Dosing is twice a day, once in the morning and once in the evening.  
The dose will be administered and dose changes made according to Section 5.1.3.  
In addition to the study drug dispensed at the Baseline visit, additional investigational 
product will be shipped directly to the subject. Confirmation of delivery to the subject will be 
made by a visiting nurse. Study drug shipment, return, and accountability will be performed 
in accordance with the drug distribution plan.  

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Subjects will have assessments completed at Week 12, Week 52, Week 104, and Week 130. 
Assessments may be completed in the clinic or off-site, at the discretion of the Principal 
Investigator. 
3.1.2 
Safety Follow-Up Period (30 [+4] Days) 
A 30 (+4) day safety follow-up telephone or telemedicine contact is to be completed for 
subjects if they do not begin to take commercially marketed trofinetide within the 30 days 
after completing the study or if they discontinue prematurely from the study. The contact 
includes assessment of concomitant medications and treatments and assessment of AEs. 
4 SUBJECT ELIGIBILITY AND WITHDRAWAL CRITERIA 
To be eligible for this study, subjects must meet all of the inclusion criteria and none of the 
exclusion criteria. 
4.1 
Inclusion Criteria 
A subject must meet all of the following inclusion criteria to be eligible for participation in 
the study: 
1. Informed consent prior to the conduct of any study procedures is required as follows: 
a. For subjects who are minors: written informed consent will be obtained from 
the legally acceptable representative (LAR). The subject should provide 
written or oral assent if deemed able by the Investigator. The process of 
obtaining informed consent will be conducted in accordance with institutional 
review board (IRB) or ethics committee (EC) policy and applicable local law. 
b. For subjects who are not minors: written informed consent will be obtained 
from the LAR or the subject if deemed able by the Investigator. If the subject 
is deemed not able to provide consent, the subject should provide written or 
oral assent if deemed able by the Investigator. The process of obtaining 
informed consent will be conducted in accordance with IRB or EC policy and 
applicable local law. 
c. The subject’s caregiver must also provide written informed consent regarding 
their participation in the study prior to participating in any study procedures. 
2. Has completed the EOT visit of the antecedent trofinetide Study ACP-2566-004 
(i.e., has completed 40 weeks) 
3. May benefit from continued treatment with open-label trofinetide in the judgment of 
the Investigator 
4. Can still swallow the study medication provided as a liquid solution or can take it by 
gastrostomy tube 

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5. The subject’s caregiver has sufficient language skills to complete the caregiver 
assessments 
Childbearing Potential 
6. Subjects of childbearing potential must abstain from sexual activity for the duration of 
the study and for at least 30 days thereafter. If a subject is sexually active or becomes 
sexually active during the study, she must use 2 clinically acceptable methods of 
contraception (e.g., oral, intrauterine device [IUD], diaphragm plus spermicide, 
injectable, transdermal or implantable contraception) for the duration of the study and 
for at least 30 days thereafter. Subject must not be pregnant or breastfeeding. 
 
4.2 
Exclusion Criteria 
A subject must meet none of the following exclusion criteria to be eligible for the study: 
1. Began treatment with growth hormone during the antecedent study  
2. Began treatment with IGF-1 during the antecedent study 
3. Began treatment with insulin during the antecedent study  
4. Has developed a clinically significant cardiovascular, endocrine (such as hypo- or 
hyperthyroidism, Type 1 diabetes mellitus, or uncontrolled Type 2 diabetes mellitus), 
renal, hepatic, respiratory, or gastrointestinal disease (such as celiac disease or 
inflammatory bowel disease) 
5. Subject is judged by the Investigator or the Medical Monitor to be inappropriate for 
the study, due to AEs, medical condition, or noncompliance with investigational 
product or study procedures in the antecedent study 
6. Has a clinically significant abnormality in vital signs at Baseline 
7. Has an average QTcF interval of >450 ms on the Baseline ECG performed before the 
first dose of trofinetide is given in the present study (i.e., the ECG performed at the 
EOT visit of the antecedent study) 
8. Has developed a clinically significant ECG finding during the antecedent study 
9. Is judged by the Investigator or the Medical Monitor to be inappropriate for the study 
for any reason 
4.3 
Subject Withdrawal of Consent 
In accordance with the Declaration of Helsinki and other applicable regulations, a subject and 
LAR consenting on behalf of a subject have the right to withdraw from the study at any time, 
and for any reason, without prejudice to her future medical care. 

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Should a subject (or LAR) request or decide to withdraw consent, every reasonable effort will 
be made to complete and report observations as thoroughly as possible up to the date of 
withdrawal, including the evaluations specified at early termination (ET) or safety follow-up 
(whichever is applicable), as outlined in Table S–1. 
4.4 
Subject or Study Discontinuation 
Subjects may be discontinued from the study for a number of reasons, including, but not 
limited to, those listed below: 
• Adverse event 
• Death 
• Increase in post-enrollment QTcF interval (defined below and in Section 6.2.4.1) 
• Lack of efficacy 
• Lost to follow-up (Section 4.5) 
• Non-compliance with study drug 
• Physician decision 
• Pregnancy 
• Protocol deviation 
• Study terminated by sponsor 
• Use of prohibited medication 
• Other 
The Sponsor reserves the right to discontinue the study at any time for any reason. Such 
reasons may be any of, but not limited to, the following: 
• Occurrence of AEs unknown to date in respect of their nature, severity, and duration 
or the unexpected incidence of known AEs 
• Medical, ethical or business reasons affecting the continued performance of the study 
Regulatory authorities also have the right to terminate the conduct of the study in their region 
for any reason. 
4.4.1 
Post-Baseline QTcF Interval Stopping Criteria 
Study drug must be discontinued in the event that a post-enrollment QTcF duration of 
≥500 ms or an increase of ≥60 ms compared to the average QTcF interval at Baseline of the 
present study (before dosing) is observed. For visits at which more than one ECG is 

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completed, the average QTcF interval of all legible ECGs will be used to determine the QTcF 
interval for that visit. 
4.4.2 
Handling of Subject Discontinuation During the Treatment Period 
Unless the subject has withdrawn consent (or the LAR has withdrawn consent on behalf of 
the subject) to be contacted for this study, every reasonable effort should be made to 
complete the ET visit and the safety follow-up (as outlined in Table S–1) if a subject 
discontinues prematurely for any reason. All information will be reported on the applicable 
pages of the electronic case report form (eCRF). 
If a subject is discontinued from the study because of an AE, every reasonable attempt should 
be made to follow and appropriately treat the subject until the AE resolves or until the 
Investigator deems the AE to be chronic or stable. For subjects who continue to be followed 
for safety, SAEs should continue to be reported as described in Section 7.4.2. All SAEs will 
continue to be followed and appropriately treated until such events have resolved or the 
Investigator deems them to be chronic or stable. 
4.5 
Subject Lost to Follow-Up 
A subject will be considered lost to follow-up if they fail to attend a scheduled visit 
(excluding the safety follow-up telephone call) and the study site is unable to contact the 
subject or caregiver.  
Every reasonable effort should be made to contact the caregiver and will include a minimum 
of 3 documented telephone calls and, if necessary, a certified letter to the subject’s last known 
mailing address or local equivalent methods. All contact attempts are to be documented in the 
source documents. 
4.6 
Concomitant Therapy 
In order to ensure that appropriate concomitant therapy is administered, it is essential that 
caregivers be instructed not to administer any medication to the subject without prior 
consultation with the Investigator (unless the subject is receiving treatment for a medical 
emergency). 
The Investigator may prescribe appropriate medication to treat AEs. The Sponsor and 
Investigator or designee will confer to determine whether it is appropriate to continue such a 
subject in the trial if a prohibited medication is prescribed. 
It is not necessary to make an effort to maintain stable regimens of concomitant medications 
and non-medicine based therapies throughout the course of the study. New medications and 
treatments may be initiated during the study, excluding the prohibited medications IGF-1, 
growth hormone, and insulin. 

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4.6.1 
Permitted and Prohibited Medications 
Prohibited medications are IGF-1, growth hormone, and insulin. Prohibitions for concomitant 
medications will be followed between the Baseline visit and EOT/ET visit. Medications that 
can prolong QT interval are not prohibited but must be used with caution. Any use of 
medications that could interfere with study conduct must be discussed with the Medical 
Monitor. 
Use of medications that could interfere with study conduct or any questions regarding 
concomitant medications must be reviewed and/or discussed with the Medical Monitor. 
Subjects who require current treatment with a prohibited medication will be withdrawn from 
the study. 
Subjects who have previously taken a prohibited medication during the study will be 
withdrawn from the study unless: 
• the prohibited medication has been discontinued AND 
• withdrawal from the study presents an unacceptable medical risk to the subject 
The justification to allow the subject to continue in the trial will be made by the 
Sponsor/Medical Monitor, with medical input from the Investigator, and will be documented. 
If a subject is allowed to remain in the trial, this will be reported as a major protocol 
deviation and not a waiver. 
5 INVESTIGATIONAL PRODUCT 
5.1 
Investigational Product Description 
The investigational product will be trofinetide oral solution. Dose will be based on weight as 
outlined in Table S–1. Trofinetide will be provided in a ready-to-use aqueous solution for oral 
administration. Doses will be administered orally or by G tube (doses administered by 
gastrojejunal [GJ] tubes must be administered through the G-port). 
5.1.1 
Formulation, Appearance, and Packaging 
The Sponsor will supply trofinetide oral solution as an aqueous, ready-to-use, 
strawberry-flavored liquid in 500 mL (16 oz) round, high-density polyethylene (HDPE) 
plastic bottles with a child-resistant closure. 
Trofinetide oral solution is a clear, pink to red-colored liquid containing 1 gram of trofinetide 
in each 5 mL. The trofinetide oral solution also contains purified water, maltitol, strawberry 
flavor, sucralose, methylparaben sodium, propylparaben sodium, and FD&C Red #40 as 
inactive ingredients. 

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Trofinetide is manufactured under current Good Manufacturing Practices. 
During the treatment period, study drug will be distributed in a quantity sufficient to ensure 
the subject has an adequate supply of study drug between study visits. 
5.1.2 
Product Storage and Stability 
Investigational product will be shipped refrigerated at a temperature between 2°C and 8°C 
(36°F and 46°F) and will be stored at this temperature. Do not freeze. 
5.1.3 
Dosing and Administration 
5.1.3.1 
Dosing 
The subject’s assigned dose for this study will be the final dose from the antecedent study. If 
the subject’s weight at the Baseline visit of the present study puts them in a new weight 
category (see Table 5–1), the Investigator may decide to increase the dose to the dose 
associated with the new weight category. Similarly, if the subject’s weight after 52 weeks in 
the present study, or thereafter puts them in a new weight category, the Investigator may 
decide to increase the dose to the dose associated with the new weight category.   
The dose may be decreased during the study for poor tolerability as discussed in 
Section 5.1.3.2. Study drug is administered twice a day, once in the morning and once in the 
afternoon or evening. There should be at least 8 hours between doses. The study drug may be 
given with or without food.  
Table 5–1 
Weight-Dosing Categories 
Weight 
Dose  
Total Daily Dose 
12-20 kg 
30 mL (6 g) BID 
60 mL (12 g) 
>20-35 kg 
40 mL (8 g) BID 
80 mL (16 g) 
>35-50 kg 
50 mL (10 g) BID 
100 mL (20 g) 
>50 kg 
60 mL (12 g) BID 
120 mL (24 g) 
Abbreviation: BID=twice daily 
Since all subjects in this study are known to have taken trofinetide without developing an 
unacceptable prolongation of the QT interval, there is no requirement to perform an ECG 
2-3 hours after the first dose. 
The day the first dose is taken will be considered Day 1 of dosing.  
Investigational product will be shipped directly to the subject. Confirmation of any delivery 
to the subject will be made by a visiting nurse. Study drug shipment, return, and 
accountability will be performed in accordance with the drug distribution plan. In addition, 

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study drug will be dispensed at the site during the Baseline visit when the visit is conducted 
in the clinic. 
5.1.3.2 
Administration of Study Drug 
Study drug is supplied in 500 mL (16 oz) bottles with a child-resistant closure. A press-in 
bottle adapter and syringe for accurately measuring the dose are supplied separately. 
Doses may be taken orally or via gastrostomy tube.  
• When study drug is given orally, it may be administered directly from a syringe or 
transferred into another container to facilitate administration. 
• For gastrojejunal tubes, medication should be given via the gastric port. The tube 
must be flushed with water after study drug administration to clear the tube of study 
drug. No more than 250 mL of water should be used. Doses should be taken over a 
10-minute period. 
If the subject cannot tolerate administration of the full assigned dose the Investigator may 
instruct the caregiver to reduce study drug to a dose as low as 3 g (15 mL) BID. In addition, 
up to 4 doses (in total, consecutive or non-consecutive) may be held for this reason.  
5.1.4 
Method of Assigning Subjects to Treatment Groups 
All eligible subjects will receive twice-daily doses of trofinetide over the duration of the 
study. Details of trofinetide dosing and administration are provided in Section 5.1.3. 
5.1.5 
Blinding 
This is an open-label study. 
5.1.6 
Study Drug Compliance 
If a subject misses one dose of study drug, she must not take an extra dose the next day. 
5.1.7 
Overdose 
An overdose is a deliberate or inadvertent administration of a treatment at a dose higher than 
the maximum recommended dose per protocol. It must be reported, irrespective of outcome, 
even if toxic effects were not observed (Section 7.4.4). All events of overdose are to be 
captured as protocol deviations. The maximum recommended dose for each subject is 
provided in Section 5.1.3. 
5.2 
Investigational Product Accountability Procedures 
The Investigator or designee will keep current and accurate records of the study drug product 
dispensed, used, and returned for each subject to assure the health authority and the Sponsor 
that the study drug is being handled appropriately. Caregivers must be instructed to return all 

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packaging to the Investigator or designee at regularly scheduled clinic or home nursing visits 
as appropriate.  
At appropriate intervals during the study, study drug reconciliation will be performed by the 
Sponsor (or designee) who may return appropriate unused study drug and used and unused 
packaging to the Sponsor’s designee for destruction. 
At the conclusion of the study, final study drug reconciliation will be conducted at the site. 
Final study drug accountability documentation will be maintained at both the site and by the 
Sponsor or designee. Any remaining unused study drug and all used and unused packaging 
will be sent back to the Sponsor’s designee for destruction or destroyed at the site, as allowed 
by country-specific regulations. Documentation of study drug destruction will be recorded 
and maintained by both the Sponsor and the Sponsor’s designee. 
The Investigator or designee is responsible for taking an inventory of each shipment of study 
drug received and comparing it with the accompanying material shipping form. The 
Investigator or designee will verify the accuracy of the information on the form, sign and date 
it, and provide a copy of it to the Sponsor or designee. Any study drug supplied is for use in 
this study only and must not be used for any other purpose. 
6 STUDY PROCEDURES 
Study-specific procedures are detailed below. All assessments will be completed according to 
the schedule described in Table S–1. Every effort should be made to complete the required 
procedures and evaluations at the designated visits and times. 
The assessments at the EOT visit of the antecedent study will serve as the Baseline 
assessment of the present study. 
6.1 
Efficacy Assessments 
All assessments will be administered in a standardized manner. Clinician completed measures 
will be completed by trained practitioners. Caregiver completed assessments will be reviewed 
by study personnel, and caregivers will receive standardized training and guidance on how to 
complete the measures. To the extent possible, all efforts should be made to maintain the 
same caregiver (i.e., caregiver rater) and clinician rater (as applicable) across visits for a 
single subject. 
6.1.1 
Rett Syndrome Behaviour Questionnaire (RSBQ) 
The Rett Syndrome Behaviour Questionnaire (RSBQ) is a 45-item caregiver-completed 
rating scale assessing a wide range of neurobehavioral symptoms known to be impaired in 
RTT (Mount et al. 2002). The RSBQ is a well-validated instrument that has been used in the 
Phase 2 study, Neu-2566-RETT-002, as well as in other observational and interventional 

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studies in RTT (Glaze et al. 2019; Khwaja et al. 2014; O’Leary et al. 2018). The RSBQ has 
been correlated with functioning and quality of life and has been characterized and validated 
across a range of ages and genetic variations in RTT (Cianfaglione et al. 2015; 2016; 
Robertson et al. 2006; Barnes et al. 2015). The scale includes 45 items, including 8 subscales, 
whose ratings reflect the severity and frequency of symptoms. The caregiver rates items as 
“0” (not true), “1” (somewhat or sometimes true) or “2” (very true). The eight subscales 
include: 
1. General mood 
2. Breathing problems 
3. Hand behavior 
4. Face movements 
5. Body rocking/expressionless face 
6. Nighttime behaviors 
7. Fear/anxiety 
8. Walking/standing 
As much as possible, caregiver raters will remain the same throughout the study.  
The RSBQ assessment will be administered at Baseline and at all other designated visits.  
6.1.2 
Clinical Global Impression–Improvement (CGI-I) and Clinical Global 
Impression–Severity (CGI-S) 
The CGI-I scale will be administered at Baseline and Visit 2. Completion of this scale 
requires the clinician to rate how much the subject’s illness has improved or worsened 
relative to a baseline state. A 7-point scale is used from 1=very much improved, 2=much 
improved, 3=minimally improved, 4=no change, 5=minimally worse, 6=much worse, 
7=very much worse.  
The CGI-I assessed in the present study will be a comparison with the subject’s condition at 
the Baseline visit of the antecedent Study ACP-2566-004. 
The CGI-S assessment will be made at Baseline and at all other designated visits. The CGI-S 
is a 7-point scale that requires the clinician to rate the severity of the subject’s illness at the 
time of assessment, relative to the clinician’s experience with subjects who have the same 
diagnosis. Considering total clinical experience, a subject is assessed on severity of illness at 
the time of rating: 1, normal, not at all ill; 2, borderline ill; 3, mildly ill; 4, moderately ill; 
5, markedly ill; 6, severely ill; or 7, extremely ill. 
In this study, the illness being assessed is Rett syndrome as a whole. 

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Following best practice, the CGI-S and CGI-I ratings for the study will be assessed using 
RTT-specific anchors across major symptom areas in the same manner as in the Phase 2 
studies (Neul et al. 2015; Busner and Targum 2007; Glaze et al. 2017; Glaze et al. 2019). 
6.1.3 
Communication and Symbolic Behavior Scales - Developmental Profile 
Infant-Toddler (CSBS-DP-IT) Checklist  
The Communication and Symbolic Behavior Scales-Developmental Profile™ (CSBS-DP) is 
standardized screening scale for assessing communication and pre-linguistic skills in young 
children 12-24 months (Wetherby et al. 2002) and can be used with older children with 
developmental delay (Anagnostou et al. 2015; Urbanowicz et al. 2016). The CSBS-DP 
includes a suite of three separate measures: The Infant-Toddler Checklist, a follow-up 
Caregiver Questionnaire and a Behavior Sample. In this study only the Infant-Toddler 
(CSBS-DP-IT) Checklist will be used. 
Given the limited communication abilities of individuals with Rett Syndrome, the 
CSBS-DP-IT Checklist was assessed and a subset of items were found to be appropriate for 
assessing communication skills of individuals with Rett syndrome 8 to 19 years of age 
(Urbanowicz et al. 2016). The CSBS-DP-IT was assessed in a Phase 2 trial of mecasermin 
(recombinant human IGF-1) a compound related to trofinetide, in children with Rett 
syndrome 2 to 10 years of age (O’Leary et al. 2018). In that study, the first 16 items were 
completed, which allowed for calculation of the Social composite score. The CSBS-DP-IT 
demonstrated evidence of benefit in subjects in the active treatment group compared to those 
in the placebo treatment group (O’Leary et al. 2018). The CSBS-DP Social composite score 
has also shown evidence of sensitivity to change in behavioral intervention studies in other 
developmental disorders (e.g., Wetherby et al. 2014; Anagnostou et al. 2015). 
The CSBS-DP-IT Checklist is a 24-item rating scale completed by the caregiver. Each item is 
scored using a three-level rating of frequency: “not yet”, “sometimes” and “often”. Three 
composite scores assessing 7 skill areas can be calculated: 1) Social Composite (including 
Emotion and Eye Gaze, Communication Rate and Function, and Gestures); 2) Speech 
Composite (including Sounds and Words); 3) Symbolic Composite (including Understanding 
and Object Use). 
All 24 items on the Infant-Toddler Checklist are to be completed by the caregiver. The 
question after item 24 (“Do you have any concerns about your child’s development?”) is not 
to be completed. At each administration, the study staff will review the instructions and 
scoring rubric with the caregiver. The Social Composite raw score, comprised of items 1 to 
13, is used for the key secondary endpoint. 

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The CSBS-DP-IT Checklist will be administered at Baseline and at all other designated 
visits.  
6.1.4 
The Quality of Life Rating of the Impact of Childhood Neurologic Disability 
(ICND) Scale 
The Impact of Childhood Neurologic Disability (ICND) Scale was developed to evaluate the 
impact that a child’s condition has on the child’s and the family’s everyday life at the present 
time and during the previous 3 months (Camfield et al. 2003). The parent or other caregiver 
evaluates the effect of a condition or health problem on 11 aspects of the child’s or the 
family’s life.  
The caregiver then rates overall quality of life of the subject by responding to the following: 
“Please rate your child’s overall ‘Quality of Life’ on the scale below. Choose the number 
which you feel is best and circle it”. The choices range from 1 (“Poor”) to 6 (“Excellent”). 
In this study, the caregiver will rate only the Quality of Life assessment of the ICND Scale. 
The assessment will be administered at Baseline and at all other designated visits. 
6.1.5 
Rett Syndrome Clinician Rating of Hand Function (RTT-HF)  
The Rett Syndrome Clinician Rating of Hand Function is a clinician completed clinical 
assessment of the subject’s ability to use her hands for functional purposes (such as reaching 
for and grasping objects, self-feeding or drawing). The assessment is made on an 8-point 
Likert scale (0-7) with 0 denoting normal functioning and 7 the most severe impairment. This 
rating is a further development of the RTT-DSC Hand Use Rating used in Study 
Neu-2566-RETT-002. 
The assessment will be administered at Baseline and at all other designated visits. 
6.1.6 
Rett Syndrome Clinician Rating of Ambulation and Gross Motor Skills 
(RTT-AMB)  
The Rett Syndrome Clinician Rating of Ambulation and Gross Motor Skills is a clinician 
completed clinical assessment of the subject’s ability to sit, stand, and ambulate 
(e.g., walking, running, climbing stairs). The assessment is made on an 8-point Likert scale 
(0-7) with 0 denoting normal functioning and 7 the most severe impairment. This rating is a 
further development of the RTT-DSC Ambulation Rating used in Study Neu-2566-RETT-
002. 
The assessment will be administered at Baseline and at all other designated visits. 

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6.1.7 
Rett Syndrome Clinician Rating of Ability to Communicate Choices 
(RTT-COMC)  
The Rett Syndrome Clinician Rating of Ability to Communicate Choices is a clinician 
completed clinical assessment of the subject’s ability to communicate her choices or 
preferences, which can include the use of nonverbal means such as eye contact or gestures. 
The assessment is made on an 8-point Likert scale (0-7) with 0 denoting normal functioning 
and 7 the most severe impairment. This rating is a further development of the RTT-DSC 
Language/Communication Rating used in Study Neu-2566-RETT-002. 
The assessment will be administered at Baseline and at all other designated visits, when the 
visit takes place in the clinic. When a study visit takes place off-site, the RTT-COMC should 
be completed if possible, but it is not required.   
6.1.8 
Rett Syndrome Clinician Rating of Verbal Communication (RTT-VCOM)  
The Rett Syndrome Clinician Rating of Verbal Communication is a clinician completed 
clinical assessment of the subject’s ability to communicate verbally (e.g., words and phrases). 
The assessment is made on an 8-point Likert scale (0-7) with 0 denoting normal functioning 
and 7 the most severe impairment. This rating is a further development of the RTT-DSC 
Language/Communication Rating used in Study Neu-2566-RETT-002. 
The assessment will be administered at Baseline and at all other designated visits. 
6.1.9 
Rett Syndrome Caregiver Burden Inventory (RTT-CBI) 
The RTT-CBI is a syndrome-specific, caregiver-completed questionnaire that is based on the 
Caregiver Burden Inventory designed for Alzheimer’s disease (Lane et al. 2017; 
Novak and Guest 1989). The scale is intended to directly address caregiver burden and 
indirectly assess the significance of treatment effects on function in the context of activities 
of daily living. Caregivers rate how often a given statement describes their feeling or 
experience. Frequency ratings are on a 5-point Likert scale including: 0-never; 1-rarely; 
2-sometimes; 3-frequently and 4-nearly always. As in the original Caregiver Burden 
Inventory, the RTT-CBI has 24 negatively worded items (items 1 through 24) yielding a total 
score up to 96. The RTT-CBI also includes 2 positively worded items (items 25 and 26) that 
comprise the Optimism Index (Lane et al. 2017). The total score is defined as the total 
Burden score (items 1-24). 
The RTT-CBI will be completed at Baseline and at all other designated visits.  

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6.2 
Safety Assessments  
6.2.1 
Physical Examination 
A general physical examination will be conducted at Baseline and at all other designated 
visits. When a study visit takes place off-site, the physical examination will not be required. 
The physical exam procedures will include the following organ systems: 
• Neurological 
• Head, ears, eyes, nose, and throat 
• Skin 
• Cardiovascular 
• Respiratory 
• Abdomen 
• Genitourinary (optional) 
• Musculoskeletal 
6.2.2 
Vital Signs 
Vital signs will include body temperature, resting respiration rate, sitting systolic and 
diastolic blood pressure, and pulse rate. The sitting blood pressure will be measured after the 
subject has been sitting for ≥3 minutes. 
Vital signs to be measured at Baseline and at all other designated visits. 
6.2.3 
Height, Weight, and Body Mass Index 
Height will be measured at Baseline and all other designated visits. 
Weight will be measured at Baseline and all other designated visits when the visit takes place 
in the clinic. When a study visit takes place off-site, weight should be measured whenever 
possible. 
Body mass index will be calculated using the following formula: 
Weight (kg) / [height (m)]2. 
6.2.4 
Electrocardiograms 
All 12-lead ECGs will be complete, standardized recordings, whenever possible. ECGs will 
be completed in triplicate at Baseline before dosing, and a single ECG will be completed at 
all other designated visits. The ECG taken at the EOT visit in the antecedent study is the 
Baseline ECG of the present study. For visits at which more than one ECG is completed, the 

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average QTcF interval of all legible ECGs will be used to determine the QTcF interval for 
that visit. 
The subject should rest for ≥5 minutes in a supine position before the ECG is obtained. If it is 
impractical to rest in supine position due to the subject’s medical condition, the subject may 
remain in a partial supine or other position (e.g., upright in wheelchair) for ≥5 minutes before 
the ECG is obtained and when the ECG is obtained. ECG tracings (paper or electronic) will 
be reviewed and interpreted by a qualified clinician for prolongation of the QTcF interval and 
for other cardiac irregularities. ECG tracings and results (ventricular rate, PR, QRS, QT, 
QTcF and QTcB intervals) will be included in the subject’s study records.  
At Baseline, the average QTcF interval of all legible ECGs will be used to determine 
eligibility. A reasonable effort should be made to obtain three ECGs. If it is not feasible or if 
completing two or three ECGs demands extraordinary effort, the clinician may stop and 
document the reason for not obtaining the three ECGs. The ECGs that have been completed 
and are legible should be transmitted to central ECG reader. ECGs will be read by a qualified 
central reader. The central reading will be the reading that is entered in the database. The 
results from the reports from the central reader will be reviewed by the Investigator. 
6.2.4.1 
Post-Enrollment QTcF Interval Stopping Criteria 
In the event that a post-enrollment QTcF duration of ≥500 ms or an increase of ≥60 ms 
compared to the average QTcF interval at Baseline of the present study (before dosing) is 
observed, study drug administration is to be discontinued. For visits at which more than one 
ECG is completed, the average QTcF interval of all legible ECGs will be used to determine 
the QTcF interval for that visit. 
6.2.5 
Laboratory Evaluations 
Laboratory evaluations will be completed according to the schedule presented in Table S–1 
and procedures detailed in the laboratory manual. Additional safety testing may be performed 
at the discretion of the Investigator or designee. 
Clinical laboratory sample collection is not required to be completed under fasting 
conditions. The laboratory evaluations will include the following: 
• Clinical chemistry serum tests 
o Sodium (Na), potassium (K), chloride (Cl), phosphorus (P), calcium (Ca), carbon 
dioxide (CO2), blood urea nitrogen (BUN), creatinine (CR), uric acid 
o Alanine aminotransferase (ALT), aspartate aminotransferase (AST), 
gamma-glutamyl transpeptidase (GGT), alkaline phosphatase (ALP), total 
bilirubin (TBIL), lactate dehydrogenase (LDH) 

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o Glucose 
o Albumin (ALB), total protein 
• Pregnancy test 
o A serum pregnancy test will be performed at all designated visits (Table S–1) for 
subjects of childbearing potential 
• Hematology tests 
o Complete blood count (CBC) including: 
 White blood cell (WBC) count 
 Complete differential (relative and absolute) 
 Hematocrit (Hct), hemoglobin, red blood cells (RBC), platelets 
 Reticulocyte count 
• Urinalysis 
o Blood, RBCs, WBCs, protein, glucose, ketones, specific gravity, pH 
o Reasonable efforts will be made to collect a urine sample from all subjects. When 
collection of a urine sample proves impractical or impossible (e.g., because the 
subject is incontinent or unable to cooperate), failure to collect a urine sample will 
be recorded in the subject’s eCRF, and will not be considered a protocol deviation 
6.3 
Caregiver Diary 
A semi-structured caregiver diary will be completed during treatment in which caregivers 
will record seizures and seizure-like spells if they are present.  
At the Baseline visit, the clinician will review subject’s seizure profile (if applicable) and 
will, if necessary, update the characterization of the subject’s typical seizure types. These are 
recorded in the caregiver diary. Dose modifications and missed or partial doses will be 
recorded in the caregiver diary. 
The caregiver diary will be completed and collected on an ongoing basis throughout the study 
from Baseline to EOT/ET. The clinician will verbally ask about AEs (see Section 7.4.1), 
review the events recorded in the diary with the caregiver and will make a clinical evaluation, 
including an evaluation of whether an AE will be reported. 
6.4 
Caregiver Interview 
An optional qualitative interview with caregivers of study subjects will be conducted 
remotely by telephone. Only caregivers of subjects for whom separate informed consent for 

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the caregiver interview is completed will be interviewed. Interviews will be conducted by 
trained moderators from a 3rd party and are anticipated to be approximately up to 60 minutes 
in duration. The interviews are planned to elicit a better understanding of the observable signs 
as well as the impact of study drug and RTT both on the study subject and on the caregiver. 
The interviews will document changes observed by the caregivers over the course of 
participation in the study and in antecedent trofinetide studies. The interviews will also 
provide an opportunity to describe the meaningfulness of any improvements that may have 
occurred from the perspective of the caregiver. Interviews will be audio-recorded and 
transcribed for analysis. Any personally identifiable health information mentioned during the 
interview will be redacted by the interviewer prior to transcription of the interview. 
Furthermore, if any potential adverse events are revealed during the interview, the 
interviewer will inform the investigator of the potential adverse event. Audio recordings of 
the interviews will be destroyed following transcription.  
Following the analysis of the qualitative data, a summary report that describes the objectives, 
methods, participants, and results of the qualitative interviews will be prepared and reported 
separately from the clinical study report.  
The caregiver interview will be administered at or before the final study visit (Week 130 
[EOT/ET]). 
7 ADVERSE EVENTS 
7.1 
Specification of Safety Parameters 
7.1.1 
Definition of Adverse Event 
An AE is defined as “any untoward medical occurrence in a patient or clinical study 
participant, temporally associated with the use of study drug, whether or not considered 
related to study drug”. 
An AE can therefore be any unfavorable and unintended sign (e.g., an abnormal laboratory 
finding), symptom, or disease temporally associated with the use of a drug, without any 
judgment about causality or seriousness. An AE can arise from any use of the drug 
(e.g., off-label use, use in combination with another drug) and from any route of 
administration, formulation, or dose, including an overdose. 
A suspected adverse reaction is any AE for which there is a reasonable possibility that the 
drug caused the AE. 
AEs do not include the following: 
• Stable or intermittent chronic conditions (such as myopia requiring eyeglasses) that 
are present prior to Baseline and do not worsen during the study 

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• Medical or surgical procedures (e.g., surgery, endoscopy, tooth extraction, 
transfusion). The condition that leads to the procedure is an AE if not present at 
Baseline. 
• Overdose of concomitant medication without any signs or symptoms unless the 
subject is hospitalized for observation; if an overdose occurs, it will be reported on an 
overdose form 
• Hospitalization for elective surgery planned prior to study (situation where an 
untoward medical occurrence has not occurred) 
• Pregnancy will not be considered an AE, but if it occurs, it will be reported on a 
pregnancy form 
7.1.2 
Definition of Serious Adverse Event 
In addition to the severity rating, each AE will be classified by the Investigator as “serious” 
or “not serious.” The seriousness of an event will be defined according to the applicable 
regulations and generally refers to the outcome of an event. An SAE is one that meets one or 
more of the following: 
• Is fatal 
• Is immediately life threatening 
• Results in disability or permanent damage 
• Requires hospitalization 
• Prolongs existing hospitalization 
• Is a congenital anomaly or birth defect (in an offspring) 
• Is medically significant 
Definition of Life Threatening 
A life-threatening event places the subject at immediate risk of death from the event as it 
occurred. This does not include an AE, which, had it occurred in a more severe form, might 
have caused death. 
Definition of Hospitalization 
Hospitalization is defined by the Sponsor as a full admission to the hospital for diagnosis and 
treatment. This includes prolongation of an existing inpatient hospitalization.  
Examples of visits to a hospital facility that do not meet the serious criteria for 
hospitalization include: 

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• Emergency room visits (that do not result in a full hospital admission) 
• Outpatient surgery 
• Preplanned or elective procedures 
• Protocol procedures 
• Social hospitalization, defined as admission to the hospital as a result of inadequate 
family support or care at the subject’s primary residence  
Definition of Disability or Permanent Damage 
Disability is defined as a persistent or significant incapacity or substantial disruption of the 
ability to conduct normal life functions. 
Definition of Medically Significant 
Important medical events (medically significant events) that may not result in death, be life 
threatening, or require hospitalization may be considered to be an SAE when, based upon 
appropriate medical judgment, they may jeopardize the subject or may require medical or 
surgical intervention to prevent one of the outcomes listed in this definition. Examples of 
such events are intensive treatment in an emergency room or at home for allergic 
bronchospasm, blood dyscrasias, or convulsions that do not result in hospitalization or 
development of drug dependency or drug abuse. 
An SAE may also include any other event that the Investigator or Medical Monitor judges to 
be serious or that suggests a significant hazard, contraindication, side effect, or precaution. 
7.2 
Classification of an Adverse Event 
7.2.1 
Severity of Event 
The severity of each AE will be graded on a 3-point scale and reported in detail as indicated 
on the eCRF: 
• Mild: awareness of sign or symptom but easily tolerated, causing minimal 
discomfort, and not interfering with normal everyday activities 
• Moderate: sufficiently discomforting to interfere with normal everyday activities 
• Severe: incapacitating and/or preventing normal everyday activities 
7.2.2 
Relationship to Study Drug 
The causality of each AE should be assessed and classified by the Investigator as “related” or 
“not related.” An event is considered related if there is a reasonable possibility that the event 

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may have been caused by the product under investigation (i.e., there are facts, evidence, or 
arguments to suggest possible causation). 
Consider the following when assessing causality: 
• Temporal associations between the agent and the event 
• Response to cessation (de-challenge) or re-challenge 
• Compatibility with known class effect 
• Known effects of concomitant medications 
• Pre-existing risk factors 
• A plausible mechanism 
• Concurrent illnesses 
7.2.3 
Duration 
The start and stop dates for AEs will be recorded using the following criteria: 
• Start: Date of the first episode of the AE or date of significant sustained worsening in 
severity 
• Stop: Date when AE either ceased permanently or changed in severity 
For AEs of diarrhea, the start date and stop date of a decrease in severity will also be 
recorded. 
7.2.4 
Frequency 
The frequency of the AE should be indicated according to the following definitions: 
• Single: Experienced once, without recurrence 
• Recurrent: More than one discrete episode with the same severity 
7.2.5 
Action Taken with Study Drug 
• Dose not changed: No change in study drug 
• Drug interrupted: Study drug temporarily stopped 
• Drug withdrawn: Study drug discontinued permanently 
• Dose decreased: Dose of study drug reduced 
7.2.6 
Therapy 
• None: No new treatment instituted 

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• Medication: New treatment initiated as a direct result of AE 
• Other: Other action required 
7.2.7 
Outcome 
• Recovered/resolved: Recovered or resolved 
• Recovered/resolved with sequelae: Recovered or resolved with sequelae 
• Not recovered/not resolved: Not recovered or not resolved 
• Fatal: Death due to an AE 
• Unknown: Unknown 
7.2.8 
Seriousness 
• Not serious 
• Serious (see Section 7.1.2) 
7.2.9 
Definition of Unexpectedness 
An AE, the nature or severity of which is not consistent with the information provided in the 
Reference Safety Information section of the current trofinetide Investigator’s Brochure. 
7.3 
Time Period and Frequency for Event Assessment and Follow-Up 
Adverse events with an onset before the first dose of open-label trofinetide in the present 
study will be recorded as an AE in the antecedent study. All ongoing AEs from the antecedent 
trofinetide study will be carried over after informed consent has been obtained for the present 
study and recorded from Baseline for the present study until resolution or the follow-up 
safety assessment. An adverse event occurring after the first dose of open-label trofinetide in 
the present study will be recorded as an AE in the present study. Adverse events for the 
present study will be recorded from the time of first dose of open-label trofinetide in the 
present study through the safety follow-up period. 
All AEs must be either resolved or stable at the end of the safety follow-up period. If an AE is 
ongoing at the end of the study safety follow-up period, every reasonable attempt should be 
made to follow and appropriately treat the subject until the AE resolves or until the 
Investigator deems the AE to be chronic or stable. 
In the event that a subject discontinues and has an ongoing AE at the time of discontinuation 
(Section 4.4.2) or is withdrawn from the study because of an AE, the subject should be 
followed and appropriately treated until the AE resolves or until the Investigator deems the 
AE to be chronic or stable. 

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7.4 
Reporting Procedures 
7.4.1 
Adverse Event Reporting 
The Investigator must record all observed AEs and all reported AEs. At each visit, the 
Investigator should ask the subject a nonspecific question (e.g., “Have you noticed anything 
different since your last visit?”) to assess whether any AEs have been experienced since the 
last report or visit. 
Note that any use of medication (and specifically any newly prescribed medication) during 
the course of a study may indicate the occurrence of an AE that may need to be recorded on 
both the AE and the concomitant medication page. 
All AEs, serious and not serious, will be recorded on the AE eCRF page using appropriate 
medical terminology. Severity and relationship to study drug will be assessed by the 
Investigator. 
When possible, clinical AEs should be described by diagnosis and not by symptoms 
(e.g., “cold” or “seasonal allergies” instead of “runny nose”). 
All AEs, whether or not related to the study drug, must be fully and completely documented 
on the AE eCRF and in the subject’s notes. 
7.4.2 
Serious Adverse Event Reporting 
The reporting of SAEs by the Sponsor or designee to the regulatory authorities is a regulatory 
requirement. Each regulatory authority has established a timetable for reporting SAEs based 
upon established criteria. 
Serious AEs must be reported within 24 hours of discovery to the Sponsor or its designee; use 
the appropriate form for initial and/or follow-up reporting.  
At a minimum, events identified by the Sponsor to require expedited reporting as serious, 
unexpected, and related to study drug must be brought to the attention of the responsible 
institutional review board/ethics committee (IRB/EC), as per applicable regulations. These 
will be provided by the Sponsor after their assessment. For European Union member states, 
the Sponsor or its designee will provide reports of suspected unexpected serious adverse 
reactions (SUSARs) directly to the ECs, as required by local legislation. In all other 
countries, it is the Investigator’s responsibility to provide these expedited reports to the 
responsible IRB/EC. It is also the Investigator’s responsibility to notify the responsible 
IRB/EC regarding any new and significant safety information. 
When an SAE occurs, Investigators will review all documentation related to the event and 
will complete the paper SAE form with all required information (for initial and/or follow-up 

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information) and fax or email (within 24 hours of discovery) to the contact information 
provided on the SAE form. 
Subjects will be followed through the safety follow-up period (i.e., 30 [+4] days after last 
dose of study drug) for any SAEs and/or other reportable information until such events have 
resolved or the Investigator deems them to be chronic or stable. 
In the event of any SAE (other than death), the study subject will be instructed to contact the 
Investigator (or designee) using the telephone number provided in the informed consent form 
(ICF). All subjects experiencing an SAE will be seen by the Investigator or designee as soon 
as is feasible following the report of the SAE. 
Serious AEs occurring after the study follow-up period (i.e., 30 [+4] days after last dose of 
study drug) should be reported if in the judgment of the Investigator there is “a reasonable 
possibility” that the event may have been caused by the product. 
SAEs should also be reported to the IRB/EC according to local regulations.  
7.4.3 
Reporting of Pregnancy 
Any subject who becomes pregnant during the study (with or without AEs) must be 
withdrawn from the study and the pregnancy must be reported on the Pregnancy form within 
24 hours of discovery to the Sponsor or its designee. Any subject who becomes pregnant 
during the study will be followed through the pregnancy outcome. 
Any AEs that are the consequence of pregnancy and which meet the criteria for serious 
should also be reported via the SAE form. 
7.4.3.1 Reporting Paternal Drug Exposure 
Paternal drug exposure is defined as a father’s exposure to a medicinal product before or 
during his partner’s pregnancy. Any paternal drug exposure cases must be reported to the 
Sponsor within 24 hours of discovery via the Pregnancy form. Any AEs that are the 
consequence of paternal drug exposure and which meet the criteria for serious must also be 
reported to the Sponsor within 24 hours of discovery via the SAE form. Since no males are 
enrolling in this study, paternal drug exposure would occur only if a male who was not a 
study subject ingested study drug. 
7.4.4 
Reporting of Overdose 
An overdose is a deliberate or inadvertent administration of a treatment at a dose higher than 
the maximum recommended dose per protocol. It must be reported to the Sponsor or 
designee on the Overdose form within 24 hours of discovery. In addition, all events of 
overdose are to be captured as protocol deviations. 

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8 CLINICAL MONITORING  
Routine monitoring of study sites is described in Section 11. 
Clinical site monitoring is conducted to ensure that the rights and well-being of human 
subjects are protected, that the reported study data are accurate, complete, and verifiable, and 
that the conduct of the study is in compliance with the currently approved protocol and 
amendment(s) as applicable, with GCP, and with applicable regulatory requirements. Details 
of the study site monitoring process are described in a separate clinical monitoring plan 
document. 
9 STATISTICAL METHODS AND DATA ANALYSIS 
9.1 
Statistical and Analytical Plans 
Statistical methods will be documented in detail in a statistical analysis plan (SAP) to be 
approved by the Sponsor prior to database lock. 
9.2 
Statistical Hypotheses 
No formal testing of hypotheses is planned; all outcomes will be summarized descriptively. 
9.3 
Sample Size Determination 
The sample size of this open-label study is not determined based on statistical considerations. 
However, subjects enrolled in the present study are those who have completed the antecedent 
study, ACP-2566-004, and rolled over to the present study. Since approximately 180 subjects 
are to be enrolled in the ACP-2566-004 study and it is expected 85% of these subjects will 
complete Study ACP-2566-004 and rollover to the present study, the number of subjects in 
the present study will be approximately 153. 
9.4 
Subject Populations for Analysis 
The Safety Analysis Set will include all subjects who received at least one dose of study drug 
in this study. This analysis set will be used for all safety as well as any descriptive efficacy 
analyses. 
9.5 
Statistical Analyses 
9.5.1 
General Approach 
All endpoints will be summarized for the Safety Analysis Set. 
Data from the EOT visit procedures of Study ACP-2566-004 will be carried over as Baseline 
information in the present study, as applicable, (e.g., not for the CGI-I).  
Continuous measurement results will be reported using the number of subjects with data 
values, mean, standard error of the mean, median, standard deviation, minimum, and 

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maximum. For each categorical outcome, the frequency and percentage of subjects in each 
category will be reported. 
9.5.2 
Primary Analyses 
Adverse events will be classified into standard terminology using the Medical Dictionary for 
Regulatory Activities (MedDRA). All AEs will be listed and TEAEs will be summarized by 
system organ class and preferred term. A TEAE is defined as an AE that started after the first 
administration of study drug and no later than the last administration of study drug plus 
30 days. Summaries by maximum severity and by relationship to study drug will also be 
provided. Serious TEAEs, fatal AEs, and TEAEs leading to discontinuation will also be 
summarized. 
Descriptive summary statistics for ECG, vital signs and body weight, and clinical laboratory 
parameters, including observed values and changes from Baseline, will be tabulated by 
timepoint. Additionally, categorical analyses will be conducted on the incidence of subjects 
with prolonged QTc intervals and changes in QTc intervals in accordance with International 
Council for Harmonisation (ICH) guidelines. 
9.5.3 
Efficacy Analyses 
Descriptive summary statistics for RSBQ (absolute values and change from Baseline), CGI-I 
(absolute values, assessed by comparing to the status at Study ACP-2566-004 baseline), 
CGI-S, CSBS-DP-IT, each of the four Rett Syndrome Clinician Rating scales, RTT-CBI, and 
ICND Quality of Life score absolute values and change from Baseline will be summarized by 
timepoint. 
9.5.4 
Subgroup Analyses 
Selected analyses may be performed in subgroups. Details will be provided in the SAP. 
9.6 
Interim Analyses 
No interim analysis is planned in this study.   
9.7 
Measures to Minimize Bias 
Not applicable. The present study is open label. 
9.8 
Breaking the Study Blind/Subject Code 
Not applicable. The present study is open label. 

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10 STUDY MANAGEMENT AND DATA COLLECTION 
10.1 Data Collection and Management Responsibilities 
All documents required for the conduct of the study as specified in the ICH GCP guidelines 
will be maintained by the Investigator in an orderly manner and made available for 
monitoring and/or auditing by the Sponsor and regulatory authorities. 
The Investigator and institution must permit authorized representatives of the Sponsor or 
designees (including monitors and auditors), regulatory authorities (including inspectors), 
and the IRB/EC direct access to source documents (such as original medical records). Direct 
access includes permission to examine, analyze, verify, and reproduce any records and 
reports that are needed for the evaluation of the study. The Investigator must ensure the 
reliability and availability of source documents from which the information on the eCRF was 
derived. 
10.2 Source Documents 
All study specific information obtained at each study visit must be recorded in the subject’s 
record (source documentation), and then entered into a validated electronic data capture 
(EDC) database by trained site personnel. The source documentation may consist of source 
notes captured by site personnel and the caregiver diaries, as well as laboratory reports, 
ECG reports, and electronic source data. 
10.3 Case Report Forms 
Subject data required by this protocol are to be recorded in an EDC system on eCRFs. The 
Investigator and his or her site personnel will be responsible for completing the eCRFs. The 
Investigator is responsible for the accuracy and reliability of all the information recorded on 
the eCRFs. All information requested on the eCRFs needs to be supplied, including subject 
identification data, visit date(s), assessment values, etc., and any omission or discrepancy will 
require explanation. All information on eCRFs must be traceable to source documentation at 
the site. 
10.4 Confidentiality 
The Investigator must ensure that each subject’s anonymity is maintained as described below. 
On the eCRFs, medical records, and other documents submitted to the Sponsor or designees, 
subjects must be identified by a subject identification number only. Subject identifiers 
uniquely identify subjects within the study and do not identify any person specifically. 
Documents that are not for submission to the Sponsor or designees (e.g., signed ICFs) should 
be kept in strict confidence by the Investigator in compliance with Federal regulations or 
other applicable laws or ICH guidance on GCP. Data collection and handling should comply 

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with the European Union General Data Protection Regulation (EU GDPR), where applicable. 
Acadia has assigned a Data Protection Officer (DPO) as per the EU GDPR. 
10.5 Study Records Retention 
Investigators are required to maintain all essential study documentation as per ICH GCP 
guidelines. This includes, but is not limited to, copies of signed, dated and completed eCRFs, 
documentation of eCRF corrections, signed ICFs, subject-related source documentation, and 
adequate records for the receipt and disposition of all study drug. Investigators should 
maintain all essential study documentation, for a period of at least 2 years following the last 
approval of marketing application in an ICH region (US, Europe, and Japan), or until at least 
2 years after the drug investigational program is discontinued, unless a longer period is 
required by applicable law or regulation. Only the Sponsor can notify an Investigator or 
vendor when any records may be discarded. Investigators should contact the Sponsor before 
destroying any files. 
10.6 Protocol Exceptions and Deviations 
No prospective entry criteria protocol deviations are allowed; all subjects must meet all 
eligibility criteria in order to participate in the study. Subjects with major eligibility protocol 
deviations identified in the antecedent study are not eligible for the present study even if the 
subject was allowed to continue in the antecedent study. 
Protocol waivers for eligibility will not be granted by the Sponsor under any circumstances. 
If, during the course of a subject’s post-enrollment participation in the trial it is discovered 
that the subject did not meet all eligibility criteria, this will be reported as a major protocol 
deviation and not a waiver. In this situation, the subject will be discontinued, unless the 
discontinuation presents an unacceptable medical risk. The justification to allow the subject 
to continue in the trial will be made by the Sponsor, with medical input from the Investigator, 
and will be documented. If allowed to remain in the trial, this will be reported as a major 
protocol deviation and not a waiver. All follow-up safety assessments must be completed and 
documented as outlined in the protocol (Section 3.1.2). The Investigator must report any 
protocol deviation to the Sponsor and, if required, to the IRB/EC in accordance with local 
regulations, within reasonable time. 
10.7 Protocol Amendments 
Changes to the protocol may be made only by the Sponsor (with or without consultation with 
the Investigator). All protocol modifications must be submitted to the site IRB/EC in 
accordance with local requirements and, if required, to regulatory authorities, as either an 
amendment or a notification. Approval for amendments must be awaited before any changes 
can be implemented, except for changes necessary to eliminate an immediate hazard to trial 

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subjects, or when the changes involve only logistical or administrative aspects of the trial. No 
approval is required for notifications. 
11 QUALITY MANAGEMENT 
11.1 Risk Management 
The Sponsor utilizes the ICH E6 (GCP) Revision 2 risk management approach that includes 
methods to assure and control the quality of the trial proportionate to the risks inherent in the 
trial and the importance of the information collected. The intent is that all aspects of this trial 
are operationally feasible and that any unnecessary complexity, procedures, and data 
collection are avoided. The Sponsor’s risk management approach includes the following 
documented activities with a focus on data and processes critical to ensure human subject 
protection and the reliability of trial results:  
• 
Risk Identification: risks to critical trial processes, governing systems, investigational 
product, trial design, data collection, and recording are identified. 
• Risk Evaluation: identified risks are evaluated by considering the following factors: 
(a) likelihood of occurrence, (b) impact on human subject protection and data 
integrity, and (c) detectability of errors. 
• Risk Control: risks that can be avoided, reduced (i.e. mitigated) or accepted are 
differentiated. Risk mitigation activities are incorporated in protocol design and 
implementation, study plans, training, processes, and other documents governing the 
oversight and execution of study activities. Where possible, predefined quality 
tolerance limits are defined to identify systematic issues that can impact subject safety 
or data integrity and deviations from the predefined quality tolerance limits will 
trigger an evaluation and possibly an action. Contingency plans are developed for 
issues with a high risk factor that cannot be avoided. 
• Periodic risk review, communication, and escalation of risk management activities are 
ongoing during trial execution and risk outcomes are reported in the clinical study 
report (CSR). 
11.2 Quality Control and Quality Assurance 
The Sponsor or designees and regulatory authority inspectors are responsible for contacting 
and visiting the Investigator for the purpose of inspecting the facilities and, upon request, 
inspecting the various records of the trial (e.g., eCRFs and other pertinent data) provided that 
subject confidentiality is respected. 
The Sponsor’s or designee’s monitor is responsible for inspecting the eCRFs at regular 
intervals throughout the study to verify adherence to the protocol; completeness, accuracy, 

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and consistency of the data; and adherence to local regulations on the conduct of clinical 
research. The monitor should have access to subject medical records and other study-related 
records needed to verify the entries on the eCRFs. 
The Investigator agrees to cooperate with the monitor to ensure that any problems detected in 
the course of these monitoring visits are resolved. 
In accordance with ICH guidance on GCP and the Sponsor’s audit plans, sites participating in 
this study may be audited. These audits may include a review of site facilities (e.g., 
pharmacy, drug storage areas, and laboratories) and review of study-related records may 
occur in order to evaluate the trial conduct and compliance with the protocol, ICH guidance 
on GCP, and applicable regulatory requirements. 
The Sponsor’s or designee’s representatives, regulatory authority inspectors and IRB/EC 
representatives who obtain direct access to source documents should also respect subject 
confidentiality, taking all reasonable precautions in accordance with applicable regulatory 
requirements to maintain the confidentiality of subjects’ identities. 
12 ETHICAL CONSIDERATIONS 
12.1 Ethical Standard 
The study will be conducted in compliance with the protocol, the Declaration of Helsinki, 
ICH GCP, and other applicable regulatory requirements (e.g., Serious Breach reporting, 
urgent safety measures, and EU GDPR). 
The study will be performed in accordance with the US Health Insurance Portability and 
Accountability Act (HIPAA) regulations, US FDA GCP Regulations (US Code of Federal 
Regulations [CFR] 21 parts 50, 54, 56, and 312), and ICH guidance on GCP (E6) and clinical 
safety data management (E2A). 
In accordance with Directive 75/318/EEC, as amended by Directive 91/507/EEC, the final 
clinical study report will be signed by an Investigator and/or Coordinating Investigator who 
will be designated prior to the writing of the clinical study report. 
12.2 Institutional Review Board/Ethics Committee 
The Investigator or designee will provide the IRB/EC with all requisite material, including a 
copy of the protocol, informed consent, and any subject information or advertising materials. 
The study will not be initiated until the IRB/EC provides written approval of the protocol and 
the informed consent and until approved documents have been obtained by the Investigator 
and copies received by the Sponsor. All amendments will be sent to the IRB/EC for 
information (minor amendment) or for submission (major amendment) before 
implementation. The Investigator will supply the IRB/EC and the Sponsor with appropriate 

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reports on the progress of this study, including any necessary safety updates, in accordance 
with the applicable government regulations and in agreement with policy established by the 
Sponsor. 
12.3 Informed Consent Process 
In accord with the provisions of the US CFR 21 part 50, and since this study involves greater 
than minimal risk but presents the prospect of direct benefit to all subjects enrolled, consent 
shall be obtained from an LAR, typically a guardian, or at least one parent, in accordance 
with local IRB requirements. Minors will be given the opportunity to assent to participation if 
and when they are considered capable of doing so by the PI and per local IRB requirements. 
Properly executed, informed consent/assent must be obtained from each LAR/subject prior to 
the final procedures being performed at the EOT visit in the antecedent study. The LAR is 
defined as “An individual or judicial or other body authorized under applicable law to 
consent on behalf of a prospective subject to the subject’s participation in the procedures 
involved in the research” (US CFR 21 part 50). 
For subjects who are minors, written informed consent will be obtained from the LAR. For 
subjects who are not minors, written informed consent will be obtained from the LAR or the 
subject if deemed able by the Investigator. When consent is being provided by an LAR, 
subject assent for participation should be documented, when possible. Assent is the 
affirmative agreement to participate in the research of a minor or of an adult who does not 
have the capacity to consent. If written assent is not possible, verbal assent is allowed and 
must be documented. If subject assent is not possible, then the site must document rationale 
for not being able to provide written or documented subject assent. 
If a subject’s 18th birthday takes place during the study and the subject is deemed able to 
consent by the Investigator, the subject should sign the informed consent. Reconsenting 
should take place if required by and in accordance with IRB or EC policy and applicable 
local law. 
The subject’s caregiver must also provide informed consent regarding their participation in 
the study prior to participating in any study procedures. 
The informed consent must, at a minimum, include the elements of consent described in the 
ICH guidance on GCP and the US CFR 21 part 50.25. A copy of the ICF planned for use will 
be reviewed by the Sponsor or designee for acceptability and must be submitted by the 
Investigator or designee together with the protocol, to the appropriate IRB/EC for review and 
approval prior to the start of the study at that investigational site. Consent forms must be in a 
language fully comprehensible to the LAR of the prospective subject. The Investigator must 

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provide the Sponsor or designee with a copy of the IRB/EC letter approving the protocol and 
the ICF before the study drug supplies will be shipped and the study can be initiated. 
The consent form must be revised if new information becomes available during the study that 
may be relevant to the subject’s willingness to continue participation. Any revision must be 
submitted to the appropriate IRB/EC for review and approval in advance of use. 
12.3.1 
Consent and Other Informational Documents Provided to Subjects 
The subject/LAR must be given a copy of the signed informed consent and the original 
maintained in the designated location at the site. 
12.3.2 
Consent Procedures and Documentation 
It is the Investigator or designee’s responsibility to obtain written informed consent from the 
subject/LAR after adequate explanation of the aims, methods, anticipated benefits, and 
potential hazards of the study. The LAR must be given ample time to decide about study 
participation and opportunity to inquire about details of the study. The IRB/EC-approved 
consent form must be personally signed and dated by the LAR with subject assent, if possible, 
and by the person who conducted the informed-consent discussion. The Investigator or 
appropriate site personnel must document the details of obtaining informed consent in the 
subject’s study documents. 
The subject’s caregiver must also indicate their understanding of the study and their role as a 
caregiver to the subject during the study. The subject’s caregiver must provide written 
consent prior to any study procedures being performed indicating their agreement to 
participate in the study in the caregiver role. 
Participation in the caregiver interview is optional. Informed consent must be obtained by the 
Investigator (or designee), as appropriate, prior to the interviewer contacting the caregiver 
and conducting the optional caregiver interview. 
Where applicable and permitted, informed consent forms may be administered remotely in 
accordance with ICH E6 and applicable regulations. 
Records related to a study subject’s participation will be maintained and processed according 
to local laws, and where applicable, the European Union General Data Protection Regulation 
(EU GDPR). The consent and study information documentation will include statements 
describing local and regional requirements concerning data privacy, and who to contact for 
questions. 

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13 PUBLICATION PLAN 
All publication rights are delineated in the Clinical Study Agreement and/or other separate 
agreements with the Investigator and/or Institution, as applicable. 
14 CONFLICT OF INTEREST POLICY 
14.1 Finance, Insurance, and Indemnity 
Arrangements for finance, insurance, and indemnity are delineated in the Clinical Study 
Agreement and/or other separate agreements with the Investigator and/or Institution, as 
applicable. 
 
 

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