Continuation Study of Long-term Safety, Tolerability, Pharmacokinetics and Efficacy of Recifercept in Achondroplasia

All participants who completed the prior study to assess long-term safety, tolerability, pharmacokinetics and efficacy, and in the opinion of the investigator, continue to have a positive risk:benefit profile, will be offered to enroll in this open-label extension (OLE) study for up to an additional 24 months of treatment.

Approximately 63 participants will be offered to continue at the previously received dose of Recifercept either

Low Dose Medium Dose High Dose

or at the therapeutic dose once it is identified.

Participants will attend the clinic monthly for 24 months. Assessments include safety, blood sampling, physical examination, vital signs, anthropometric body measurements \& patient/caregiver quality of life questionnaires.


Eligibility Criteria:
Inclusion Criteria:

* Male and female participants between the ages of \>15 months to \<12 years inclusive, at Visit 1 (Screen 1).
* Participants who are willing and able to comply with all scheduled visits, treatment plan, laboratory tests lifestyle considerations and other study procedures.
* Completed the C4181005 Phase 2 study.
* Able to stand independently for height measurements (if ≥2 years of age at enrollment).

Exclusion Criteria:

* Presence of co-morbid conditions or circumstances that, in the opinion of the investigator, would affect interpretation of growth data or ability to complete the trial procedures.
* Other medical or psychiatric condition including recent (within the past year) or active suicidal ideation/behavior or laboratory abnormality that may increase the risk of study participation or, in the investigator's judgment, make the participant inappropriate for the study.
* Presence of severe obesity (body mass index (BMI) \>95th percentile on Hoover-Fong BMI charts) \[Hoover-Fong et al, 2008\].
* Known closure of long bone growth plates (cessation of height growth).
* Body weight \>45 kg.
* History of hypersensitivity to study intervention or any excipients.
* History of any prior treatment with human growth hormone or related products (including insulin-like growth factor 1 \[IGF-1\]).
* History of receipt of any treatment that are known to potentially affect growth (including oral steroids \>5 days in the last 6 months, high dose inhaled corticosteroids (\>800 mcg/day beclometasone equivalent) and medication for attention deficit hyperactivity disorder).
* History of limb lengthening surgery (defined as distraction osteogenesis/Ilizarov/callostasis technique following submetaphyseal osteotomy to extend bone length).
* Any limb lengthening/corrective orthopaedic surgery planned at any point during the trial period.
* Less than 6 months since fracture or surgical procedure of any bone determined from the screening visit date.
* Presence of any internal guided growth plates/devices.
* History of removal of internal guided growth plates/devices within less than 6 months.
* History of receipt of any other (except recifercept) investigational product for achondroplasia or that may affect growth/interpretation of growth parameters.
* History of receipt of an investigational drug (not for achondroplasia/growth affecting) within the last 30 days (or as determined by the local requirement) or 5 half-lives preceding the first dose of study intervention used in this study (whichever is longer).