# Electro-Clinical Features and Functional Connectivity Analysis in SYN1-Related Epilepsy

Vincent Moya Quiros, Ahmed Adham, Philippe Convers, Gaetan Lesca, François Mauguiere, Hugo Soulier, Alexis Arzimanoglou, Allan Bayat, Hilde Braakman, Jean-philippe Camdessanche, et al.

► To cite this version:

Vincent Moya Quiros, Ahmed Adham, Philippe Convers, Gaetan Lesca, François Mauguiere, et al. Electro-Clinical Features and Functional Connectivity Analysis in SYN1-Related Epilepsy. Annals of Neurology, 2024, 97 (1), pp.34 - 50. 10.1002/ana.27063. hal-04876545

HAL Id: hal-04876545

https://ut3-toulouseinp.hal.science/hal-04876545v1

Submitted on 9 Jan 2025

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
<figure><img src="image_2.png" /></figure>

# Electro-Clinical Features and Functional Connectivity Analysis in SYN1-Related Epilepsy

Vincent Moya Quiros, MD ID,¹ Ahmed Adham, MD,²,³ Philippe Convers, MD,¹,⁴

Gaetan Lesca, MD, PhD ID,⁵,⁶

François Mauguiere, MD, PhD,⁴,⁷ Hugo Soulier, MD,¹ Alexis Arzimanoglou, MD, PhD,⁸,⁹

Allan Bayat, MD, PhD,¹⁰,¹¹,¹²,¹³ Hilde Braakman, MD, PhD ID,¹⁴

Jean-Philippe Camdessanche, MD, PhD,¹ Philippe Casenave, MD,¹⁵

Laurence Chaton, MD,¹⁶ Yves Chaix, MD, PhD,¹⁷,¹⁸ Maxime Chochoi, MD,¹⁶

Christel Depienne, PhD,¹⁹ Vincent Desportes, MD, PhD,²⁰ Jessie De Ridder, MD,²¹

Vera Dinkelacker, MD, PhD,²² Elena Gardella, MD, PhD ID,¹⁰,¹¹

Gerhard J. Kluger, MD, PhD,²³ Julien Jung, MD, PhD ID,⁷,²⁴ Martine Lemesle Martin, MD,²⁵

Maria Margherita Mancardi, MD, PhD,²⁶ Markus Mueller, MD,²⁷ Anne-Lise Poulat, MD,²⁰

Konrad Platzer, MD ID,²⁸ Agathe Roubertie, MD, PhD ID,²⁹ Marijn F. Stokman, MD, PhD,³⁰

Anneke T. Vulto-van Silfhout, MD, PhD,³⁰ Gert Wiegand, MD, PhD,³¹,³² and

Laure Mazzola, MD, PhD¹,⁴

<figure><img src="image_3.png" /></figure>

[Color figure can be viewed at www.annalsofneurology.org]

**Objective:** There is currently scarce data on the electroclinical characteristics of epilepsy associated with synapsin 1 (SYN1) pathogenic variations. We examined clinical and electro-encephalographic (EEG) features in patients with epilepsy and SYN1 variants, with the aim of identifying a distinctive electroclinical pattern.

**Methods:** In this retrospective multicenter study, we collected and reviewed demographic, genetic, and epilepsy data of 19 male patients with SYN1 variants. Specifically, we analyzed interictal EEG data for all patients, and electro-clinical data from 10 epileptic seizures in 5 patients, using prolonged video-EEG monitoring recordings. Inter-ictal EEG
functional connectivity parameters and frequency spectrum of the 10 patients over 12 years of age, were computed and compared with those of 56 age- and sex-matched controls.

**Results:** The main electroclinical features of epilepsy in patients with SYN1 were (1) EEG background and organization mainly normal; (2) interictal abnormalities are often rare or not visible on EEG; (3) more than 60% of patients had reflex seizures (cutaneous contact with water and defecation being the main triggers) isolated or associated with spontaneous seizures; (4) electro-clinical semiology of seizures was mainly temporal or temporo-insulo/perisylvian with a notable autonomic component; and (5) ictal EEG showed a characteristic rhythmic theta/delta activity predominating in temporo-perisylvian regions at the beginning of most seizures. Comparing patients with SYN1 to healthy subjects, we observed a shift to lower frequency bands in power spectrum of interictal EEG and an increased connectivity in both temporal regions.

**Interpretation:** A distinct epilepsy syndrome emerges in patients with SYN1, with a rather characteristic clinical and EEG pattern suggesting predominant temporo-insular involvement.

ANN NEUROL 2025;97:34–50

Synapsins are a group of presynaptic phosphoproteins predominantly expressed in the central and peripheral nervous systems.¹ They have a crucial role in synaptogenesis and synaptic plasticity.¹,² Synapsin 1 (SYN1) gene codes for 1 of the 3 synapsins. Pathogenic variations in SYN1 are associated with X-linked neurodevelopmental disorders mainly affecting male subjects, with clinical heterogeneity and intrafamilial variability. Currently, 85 (73 male and 12 female) cases have been reported in 50 families.²⁻²² Epilepsy, speech delay, learning disabilities, intellectual disability (ID), autism spectrum disorder (ASD), and attention-deficit/hyperactivity disorder (ADHD) are the most frequent clinical features associated with SYN1 pathogenic variations.¹⁵,²¹,²³,²⁴

Epilepsy is one of the main features reported in recent studies that concern up to 82% of patients with SYN1

variants.²¹ The presence of reflex seizures is one of the most distinctive clinical manifestations. In more than half of the described cases, seizures are triggered by cutaneous contact with water, such as bathing or showering. Other triggers are also mentioned, such as rubbing with a towel, haircutting, fingernail clipping, mental representation of bathing, toothbrushing, defecating, and laughing.³,⁵,¹⁵,¹⁹–²¹,²⁵,²⁶ Spontaneous seizures are frequently associated and psychogenic non-epileptic seizures (PNES) are reported.⁵,²⁰

Despite this knowledge about the general characteristics of epilepsy related to SYN1, comprehensive data focusing on electroclinical features are scarce, imprecise, and sometimes contradictory. The type of epilepsy is not sufficiently well characterized, with variable seizure types reported, both focal and generalized, clinical descriptions being mostly vague and succinct, based mainly on family

View this article online at wileyonlinelibrary.com. DOI: 10.1002/ana.27063

Received Mar 9, 2024, and in revised form Aug 7, 2024. Accepted for publication Aug 7, 2024.

Address correspondence to Dr Laure Mazzola, Service de Neurologie, Neurophysiologie Clinique et Epilepsie, Centre Hospitalier Universitaire de Saint Etienne, France, Hôpital Nord, 42055 Saint-Etienne cedex 02, France. E-mail: laure.mazzola@chu-st-etienne.fr

Dr Vincent Moya Quiros Service de Neurologie, Neurophysiologie Clinique et Epilepsie, Centre Hospitalier Universitaire de Saint Etienne, France, Hôpital Nord, 42055 Saint-Etienne cedex 02, France. E-mail: vincent.moya.quiros@etu.univ-st-etienne.fr

From the ¹Neurology Department, University Hospital, Saint-Etienne, France; ²Physical Medicine and Rehabilitation Department, University Hospital of Saint-Étienne, Saint-Étienne, France; ³CEA, LETI, CLINATEC, University Grenoble Alpes, Grenoble, France; ⁴NeuroPain Lab, Lyon Neuroscience Research Centre, CRNL—INSERM U 1028/CNRS UMR 5292, University of Lyon, Lyon, France; ⁵Department of Genetics, Member of the ERN EpiCARE, Hospices Civils de Lyon, Bron, France; ⁶Institute NeuroMyoGène, Laboratoire Physiopathologie et Génétique du Neurone et du Muscle, CNRS UMR 5261-INSERM U1315, Université de Lyon—Université Claude Bernard Lyon 1, Lyon, France; ⁷Department of Functional Neurology and Epileptology, Member of the ERN EpiCARE, Hospices Civils de Lyon, Université de Lyon, Lyon, France; ⁸Department of Clinical Epileptology, Sleep Disorders and Functional Pediatric Neurology, coordinating member of the ERN EpiCARE, University Hospitals of Lyon (HCL), Lyon, France; ⁹Sección Epilepsia, Sueño y Neurofisiología, Department of Neurology, coordinating member of the ERN EpiCARE, Hospital Sant Joan de Déu Barcelona, Barcelona, Spain; ¹⁰Institute for Regional Health Services, University of Southern Denmark, Odense, Denmark; ¹¹Department of Epilepsy Genetics and Personalized Medicine, Danish Epilepsy Center, Member of the ERN EpiCARE, Dianalund, Denmark; ¹²Department of Drug Design and Pharmacology, University of Copenhagen, Copenhagen, Denmark; ¹³Department of Clinical Genetics, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark; ¹⁴Department of Paediatric Neurology, Radboud University Medical Centre, Amalia Children's Hospital, Nijmegen, The Netherlands; ¹⁵Department of Neurology, Hospital Libourne, Libourne, France; ¹⁶Department of Neurology, Neurophysiology Unit, CHU Lille, Lille, France; ¹⁷Toulouse Neurolmaging Center, University of Toulouse, INSERM, Université Paul Sabatier, Toulouse, France; ¹⁸Pediatric Neurology Unit, Children's Hospital, Toulouse-Purpan University Hospital, Toulouse, France; ¹⁹Institute of Human Genetics, University Hospital Essen, University Duisburg-Essen, Essen, Germany; ²⁰Hospices Civils de Lyon, Department of Pediatric Neurology, Member of the ERN EpiCARE, Hôpital Femme Mère Enfant, Lyon, France; ²¹Department of Neurology, Academic Center for Epileptology, Kempenhaeghe, Heeze, The Netherlands; ²²Department of Neurology, University Hospital Strasbourg, Strasbourg, France; ²³Schön Klinik Vogtareuth, Center for Pediatric Neurology, Neurorehabilitation and Epileptology, Collaborating Partner of the ERN EpiCARE, PMU, Vogtareuth, Salzburg, Germany; ²⁴Department of Neurology, University Hospital, Lyon Neuroscience Research Center (CRNL), INSERM U1028, CNRS UMR5292, Lyon, France; ²⁵Department of Neurophysiology, University Hospital Dijon, Dijon, France; ²⁶Unit of Child Neuropsychiatry, Epilepsy Center, Member of the ERN EpiCARE, Istituto Giannina Gaslini, Department of Neurosciences, Rehabilitation, Ophthalmology, Genetics and Maternal and Child Health, University of Genoa, Genoa, Italy; ²⁷Department of Epileptology, Krankenhaus Mara, Bethel Epilepsy Center, Bielefeld University, Bielefeld, Germany; ²⁸Institute of Human Genetics, University of Leipzig Medical Center, Leipzig, Germany; ²⁹Department of Pediatric Neurology, INSERM, University Hospital Montpellier, Montpellier, France; ³⁰Department of Human Genetics, Radboud University Medical Center, Nijmegen, The Netherlands; ³¹Division of Pediatric Neurology, Department of Pediatrics, Asklepios Klinik Nord-Heidberg, Hamburg, Germany; and ³²Department of Pediatric and Adolescent Medicine II (Neuropediatrics, Social Pediatrics), University Medical Centre Schleswig-Holstein, Kiel, Germany
and caregiver reports. Very few seizures have been documented by video-EEG. Ictal video-EEG data are reported in only 6 patients,⁵,¹⁰,¹⁵,²⁵ and ictal EEG from an ambulatory home EEG in 1 patient.²⁶ To our knowledge, no study has specifically examined the EEG features of epilepsies associated with *SYN1* variants. In this study, we report EEG data from 19 patients with *SYN1*-related epilepsy. Video-EEG data from 10 seizures in 5 patients were analyzed and compared with literature data, with the aim of identifying a characteristic electroclinical pattern. We also described the principal interictal EEG abnormalities, their type, and distribution.

As brain connectivity organization can be affected in patients with epilepsy,²⁷⁻³² we also studied the interictal functional connectivity of these patients and compared it with data from 56 age- and sex-matched controls (for patients over 12 years of age). The epileptic networks in focal epilepsies are mostly associated to a focal increase of functional connectivity markers, and a global decrease is linked to neurocognitive disorders.²⁷,²⁹,³² We aimed to determine if connectivity networks would be affected by the epileptic process and/or altered due to the neurocognitive disorders found in patients with *SYN1*-related epilepsy. Thus, we compared brain connectivity maps and network connectivity parameters between patients with *SYN1* variants and a matched group of healthy control subjects. We also analyzed the interictal EEG powerspectrum.

We aimed to further delineate the electroclinical patterns of individuals with *SYN1* pathogenic variations, with the goal of characterizing interictal and ictal EEG patterns. Our findings will help clinicians to diagnose *SYN1*-related epilepsy earlier, to better understand the underlying pathophysiological mechanisms which would improve future management.

# Methods

## Participant Recruitment

**Patients With SYN1 Pathogenic Variations.** All patients met the following inclusion criteria: (1) having a likely pathogenic or pathogenic variation of *SYN1* identified by gene panels or exome sequencing; (2) presenting with epilepsy (related to the *SYN1* variant); (3) having benefited from EEG recordings with interictal +/- video-EEG ictal data available for review; and (4) availability of detailed clinical data, including neurodevelopmental assessment, neuropsychological and behavioral tests, brain magnetic resonance imaging, epilepsy phenotype, and response to treatment.

Recruitment was made through announcements in epilepsy networks, such as the European Reference Network for rare and complex epilepsies (ERN EpiCARE) and French League Against Epilepsy (LFCE). We also contacted the authors of the largest patient series with *SYN1* variants, published recently, and focusing on genotype/phenotype correlations, to ask if EEG data were available.²¹ All procedures were performed respecting the ethical standards of the institutional and/or national research committees, and in conformity with the 1964 Helsinki Declaration or comparable ethical standards. Data collection was approved by the University Hospital of Saint-Etienne Medical Ethics Review Committee (IRBN662023/CHUSTE). Patients and/or legal guardians were informed about inclusion in the study.

A total of 19 patients were included. Five patients were documented for the first time, and 14 had already been reported in another study.¹⁵,²¹ They came from 13 different centers located in 5 European countries. Ictal video-EEG was available for 5 patients and data from 10 seizures were analyzed.

**Controls for Interictal Functional Connectivity Analysis.** The 56 control subjects had a standard EEG recording performed with 19 electrodes (Micromed, Treviso, Italy) at the University Hospital of Saint-Etienne. They were matched to the patients for age and gender. They were selected from our EEG database. The healthy controls had no history of epilepsy, neurologic disorders, EEG, or neuro-imaging abnormalities. Taking into account that the connectivity networks evolve during the first years of life, thus making interpretation difficult, healthy subjects were all aged over 12 years old.³³ Patients with *SYN1* pathogenic variations younger than 12 years old were excluded from this analysis. EEG of control subjects had to include at least 5 minutes of artifact-free open-eyed resting recording. The analysis could so be performed in 10 patients.

## Demographic, Genetic, and Epilepsy Data

After anonymization of patients' data, each referring physician provided detailed neurological, developmental, and behavioral history. We collected information about the age at the time of study, the sex, and the characteristics of the *SYN1* variants. Regarding comorbidities, we assessed ID, ASD, and ADHD, other behavioral issues, and learning difficulties. Related to the epilepsy, we investigated the age at seizure onset, the seizure type(s) at onset and during disease course (as described by family and caregivers), the history of febrile seizures and status epilepticus, the seizure frequency, the presence of reflex seizures and the triggers
involved, the occurrence or not of spontaneous seizures, the previous and current anti-seizure medications, and overall response to treatment.

Receiver operating characteristics (ROC) and area under the curve (AUC) analyses were used to assess if the age at epilepsy onset could be predictive of ID or of response to antiseizure medications. The possible association between having an ID and a drug-resistant epilepsy was assessed using a Cochran–Armitage test.

## EEG Data

**Inter-Ictal and Ictal EEG Data Recordings.** Patients' EEG data were recorded in each participating center, then anonymized and sent in a Micromed, Natus, or edf format for analysis. EEGs were obtained using 19 electrodes placed according to the 10/20 international system (Fp1, Fp2, F3, F4, C3, C4, P3, P4, O1, O2, F7, F8, T3, T4, T5, T6, Fz, Cz, and Pz), or using 11 electrodes (Fp1, Fp2, C3, C4, F7, F8, T5, T6, O1, O2, and Cz) and a reference. Signal was acquired at 256 Hz sampling, amplified (1,000 times) and filtered to the 0.01 to 97 hertz (Hz) band. Interictal EEG features and ictal patterns analysis were performed by 2 neurophysiologists/epileptologists who completed an EEG reading chart for systematic data collection.

Electro-cardiographic modifications during seizures were also evaluated. Tachycardia was defined as an RR interval decrease over the baseline mean – 1 standard deviation (SD), and bradycardia as a RR interval increase over the baseline mean + 1 SD.³⁴

**Inter-Ictal Functional Connectivity Data Analysis.** Inter-ictal EEG analysis was done in MATLAB 2019b, with the EEGLAB Toolbox. Continuous EEG recordings were bandpass-filtered between 0.01 and 97 Hz using a finite impulse response filter. A Notch filter was also applied at 50 Hz to remove line noise artifact. The data were referenced to infinite source with the REST algorithm.³⁵ A manual slicing of the EEG was then realized by a neurophysiologist to eliminate time periods with muscle artifacts. Eye artifacts were also removed manually.

At first, we computed simple Fourier's transformation to extract the spectral power for each electrode, for each patient (n = 10) and for each frequency band. We then averaged the data respectively for each group.

For connectivity computation, the broadband time-domain source signals were band-pass filtered at 10 Hz (± 2 Hz). A space Laplacian filter was applied to the data to minimize the effects of volume conduction. A Hilbert transform was then applied, before assessing connectivity with the Phase Locking Value (PLV). The

PLV is a normalized value, that gives for each pair of electrodes a value ranging from 0 (no phase locking) to 1 (complete phase locking). For visual comparison and plotting, we then eliminated links that were weaker than 1 SD from the mean PLV value, which kept only the strongest links.

Some important markers of connectivity inside the network are the clustering coefficient and the path length value.³⁶,³⁷ The path length refers to the minimal number of edges that must be traversed to travel from one node in the network to another and the clustering coefficient is defined as the connection probability of nearest neighbor nodes. A short average path length and a high average clustering coefficient are correlated to an efficient brain network. We computed the average path length and clustering coefficient from the connectivity PLV matrixes, thanks to the toolbox BCT in MatLAB.³⁸,³⁹

## Results

### Clinical and Genetic Data

Our 19 patients came from 16 different families. Patients VIII-1 and VIII-2, as well as II-1, II-2, and II-3 were, respectively, brothers. Demographic, clinical, and genetic data are summarized in Tables 1 to 3.

SYN1 variant types included frameshift (n = 11; 58%), nonsense (n = 3; 16%), missense (n = 2; 11%), splice site (n = 2; 11%), or inframe deletion (n = 1; 5%). Eighty-four percent (n = 16/19) of patients had truncating variants of which 19% (n = 3/16) had a moderate or severe ID, and 16% (n = 3/19) had non-truncating variants among whom 33% (n = 1/3) had a moderate or severe ID (Fig 1). All individuals had maternal inheritance, except for 2 patients with a de novo variation. Medical information was available for the large majority of carrier mothers', none being reported as suffering from epilepsy.

All patients were male subjects. The mean age at last follow up was 14.6 years (range from 21 months to 32 years old). A total of 8 of 19 patients (42%) had an ID ranging from mild (n = 4), moderate (n = 2), to severe (n = 2). Learning disabilities were reported in 16 patients (84%). All patients younger than 5 years old (n = 3) presented with a language delay. ASD was diagnosed in 16% (3/19) and ADHD in 32% (6/19). No major neuroimaging abnormality was noticed.

The onset of epileptic seizures ranged from 6 months to 13 years of life, with a median age at onset of 4.5 years. In 11% of cases (n = 2), seizure-onset occurred before the second year of life, and in 47%
<table><caption>TABLE 1. Genetic, Clinical, Neurodevelopmental, and Epileptic Data, Patients I-1 to V-1</caption><thead><tr><th>Patient</th><th>I-1<sup>a</sup></th><th>II-1<sup>a</sup></th><th>II-2<sup>a</sup></th><th>II-3<sup>a</sup></th><th>III-1</th><th>IV-1<sup>a</sup></th><th>V-1<sup>a</sup></th></tr></thead><tbody><tr><td>Age at the time of the study, gender</td><td>11 yr, M</td><td>16 yr, M</td><td>21 yr, M</td><td>19 yr, M</td><td>29 yr, M</td><td>11 yr, M</td><td>15 yr, M</td></tr><tr><td>City/country of collected data</td><td>Saint-Etienne/France</td><td>Saint-Etienne/France</td><td>Saint-Etienne/France</td><td>Saint-Etienne/France</td><td>Lyon/France</td><td>Lyon and Dijon/France</td><td>Lille/France</td></tr><tr><td>Mutation type</td><td>Frameshift</td><td>Nonsense</td><td>Nonsense</td><td>Nonsense</td><td>Frameshift</td><td>Frameshift</td><td>Missense</td></tr><tr><td>SYN1 variant; (NM_006950.3); inheritance</td><td>c.1321dup; p. (Ala441Glyfs*243); Mat</td><td>c.1447C > T; p. (Gln483*); Mat</td><td>c.1447C > T; p. (Gln483*); Mat</td><td>c.1447C > T; p. (Gln483*); Mat</td><td>c.122del; p. (Gly41Glufs*103); Mat</td><td>c.1794_1906del; p. (Thr601Glufs*45); Mat</td><td>c.774G > T; p. (Met258Ile); Mat</td></tr><tr><td>Development - learning disabilities</td><td>Moderate language delay</td><td>Language delay, executive disorder, multi days</td><td>Language delay, multi days</td><td>Executive disorder, multi days</td><td>Normal</td><td>Severe ID</td><td>Mild ID</td></tr><tr><td>Behavioral disturbances</td><td>Intolerance to frustration</td><td>No</td><td>ADHD</td><td>No</td><td>No</td><td>ASD</td><td>Impulsive behavior</td></tr><tr><td>Neurological examination abnormalities</td><td>No</td><td>Tics</td><td>No</td><td>No</td><td>No</td><td>Stereotypies, hypotonia, ataxia</td><td>No</td></tr><tr><td>Neuroimaging abnormalities (MRI)</td><td>No</td><td>No</td><td>No</td><td>No</td><td>No</td><td>No</td><td>No</td></tr><tr><td>Age at seizure onset</td><td>10 mo</td><td>11 yr</td><td>7 yr</td><td>13 yr</td><td>6 yr</td><td>6 mo</td><td>11 yr</td></tr><tr><td>Suspected seizure type based on medical reports</td><td>Focal with rare secondary GTCS</td><td>Focal with rare secondary GTCS</td><td>Focal with frequent secondary GTCS</td><td>Focal with possible secondary GTCS</td><td>Focal with rare secondary GTCS</td><td>Focal with possible secondary GTCS</td><td>Focal sensory</td></tr><tr><td>Presence of reflex seizures/triggers</td><td>Yes/bathing</td><td>Yes/showering with warm water</td><td>Yes/showering with warm water</td><td>Yes/showering with warm water</td><td>Yes/defecating</td><td>No</td><td>Yes</td></tr><tr><td>SS, FS, and SE</td><td>SS and FS</td><td>SS</td><td>SS</td><td>SS</td><td>SS</td><td>SS</td><td>No</td></tr><tr><td>Frequency of seizures</td><td>Once a week</td><td>Once a week</td><td>Once a week</td><td>Once a week</td><td>Stopped with treatment</td><td>Daily</td><td>Only once</td></tr><tr><td>Current/Previous anti-seizure medications</td><td>VPA, LTG, CBD/CLB, CBZ, LEV</td><td>LEV/CLB, LTG</td><td>OXC/BRV, CLB, LAC, VPA</td><td>LTG/CLB</td><td>OXC, LEV, LAC/CBZ, PER, ZNS</td><td>ZNS, VPA, CLN/TPM, LEV</td><td>No</td></tr><tr><td>Drug resistance</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Yes</td><td>No</td><td>Yes</td><td>No</td></tr><tr><td>Intertical EEG</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Yes</td></tr><tr><td>Ictal EEG/Number of seizures</td><td>Yes/3</td><td>Yes/1</td><td>No</td><td>No</td><td>Yes/1</td><td>Yes/2</td><td>No</td></tr></tbody></table>

ADHD = attention-deficit/hyperactivity disorder; ASD = autism spectrum disorder; BRV = brivaracetam; CBD = cannabidiol; CBZ = carbamazepine; CLB = clobazam; CLN = clonazepam; DN = de novo; ECB = eslicarbazepine; F = female; FS = febrile seizures; GTCS = generalized tonic-clonic seizures; ID = intellectual disability; LAC = lacosamide; LEV = levetiracetam; LTG = lamotrigine; M = male; Mat = maternal; mo = months; MRI = magnetic resonance imaging; MVD = moderate ventricular dilatation; NA = not available; OXC = oxcarbazepine; TPM = topiramate; PER = perampanel; SE = status epilepticus; SS = spontaneous seizures; STM = sulthiame; VGB = vigabatrin; VPA = valproic acid; y = years; ZNS = zonisamide.

(n = 9) within the first 5 years of age. An early age of seizure onset (before 5 years old) was associated with an increased risk for moderate to severe ID (p < 0.036, AUC = 85%, IC = 70 à 100%). Sixty percent

(n = 6/10) of the patients with epilepsy onset before the age of 5 years presented with an associated ID versus 22% (n = 2/9) in the rest of the cohort (see Fig 1). An age under 10 years at seizure onset was found in 81%

<footnote><sup>a</sup>Refers to patients yet published in the following article: Parenti I, Leitão E, Kuechler A, et al. The different clinical facets of SYN1-related neurodevelopmental disorders. Front Cell Dev Biol 2022; 10: 1019715.</footnote>

<footnote><sup>b</sup>Refers to patients yet published in the following article: Accogli A, Wiegand G, Scala M, et al. Clinical and Genetic Features in Patients With Reflex Bathing Epilepsy. Neurology 2021; 97 (6): e577–e586.</footnote>
<table><caption>TABLE 2. Genetic, Clinical, Neurodevelopmental, and Epileptic Data, Patients VI-1 to X-1</caption><thead><tr><th>Patient</th><th>VI-1<sup>a</sup></th><th>VII-1<sup>a</sup></th><th>VIII-1<sup>a</sup></th><th>VIII-2<sup>a</sup></th><th>IX-1</th><th>X-1</th></tr></thead><tbody><tr><td>Age at the time of the study, gender</td><td>28 yr, M</td><td>9 yr, M</td><td>17 yr, M</td><td>32 yr, M</td><td>10 yr, M</td><td>20 yr, M</td></tr><tr><td>City/country of collected data</td><td>Lille/France</td><td>Strasbourg/France</td><td>Montpellier/France</td><td>Libourne/France</td><td>Genova/Italy</td><td>Bielefeld/Germany</td></tr><tr><td>Mutation type</td><td>Missense</td><td>Frameshift</td><td>Frameshift</td><td>Frameshift</td><td>Splice</td><td>Splice</td></tr><tr><td>SYN1 variant; (NM_006950.3); inheritance</td><td>c.614 T &gt; A; p. (Leu205Gln); Mat</td><td>c.39del; p. (Phe13Leufs*10); Mat</td><td>c.975del; p. (Tyr326Thrfs*2); Mat</td><td>c.975del; p. (Tyr326Thrfs*2); Mat</td><td>c.527 + 1G &gt; T; Mat</td><td>c.838-2A &gt; G; Mat</td></tr><tr><td>Development - learning disabilities</td><td>Normal</td><td>Moderate ID</td><td>Language delay, dyslexia</td><td>Normal</td><td>Mild ID, language delay</td><td>Executive disorder</td></tr><tr><td>Behavioral disturbances</td><td>Impulsive behavior</td><td>Anxiety, hyperkinetic</td><td>ADHD</td><td>Aggressive behavior</td><td>No</td><td>ADHD</td></tr><tr><td>Neurological examination abnormalities</td><td>No</td><td>No</td><td>No</td><td>No</td><td>Stereotypies</td><td>No</td></tr><tr><td>Neuroimaging abnormalities (MRI)</td><td>No</td><td>No</td><td>Enlarged Virchow-Robin</td><td>MVD, small hypophysis</td><td>No</td><td>No</td></tr><tr><td>Age at seizure onset</td><td>11 yr</td><td>1 y 6 mo</td><td>3 yr</td><td>7 yr</td><td>5 yr</td><td>7 yr</td></tr><tr><td>Suspected seizure type based on medical reports</td><td>GTCS</td><td>Focal with possible secondary GTCS</td><td>Myoclonic</td><td>GTCS</td><td>Behavior arrest of unknown onset</td><td>GTCS</td></tr><tr><td>Presence of reflex seizures/triggers</td><td>Yes/defecating</td><td>Yes/stroboscope</td><td>No</td><td>Yes/emotions and lightning</td><td>No</td><td>No</td></tr><tr><td>SS, FS, and SE</td><td>SS and FS</td><td>SS and FS</td><td>SS and FS</td><td>SS</td><td>SS</td><td>SS</td></tr><tr><td>Frequency of seizures</td><td>Stopped with treatment</td><td>NA</td><td>Only once</td><td>1-2 seizures/yr</td><td>Monthly</td><td>Stopped with treatment</td></tr><tr><td>Current/previous antiseizure medications</td><td>LTG, OXC</td><td>LEV</td><td>VPA</td><td>LTG/VGB, VPA</td><td>LEV, VPA</td><td>LAC</td></tr><tr><td>Drug resistance</td><td>No</td><td>No</td><td>No</td><td>Yes</td><td>Yes</td><td>No</td></tr><tr><td>Interictal EEG</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Yes</td></tr><tr><td>Ictal EEG/number of seizures</td><td>No</td><td>No</td><td>No</td><td>No</td><td>No</td><td>No</td></tr></tbody></table>

ADHD = attention-deficit/hyperactivity disorder; EEG = encephalographic; FS = febrile seizures; GTCS = generalized tonic-clonic seizures; ID = intellectual disability; LAC = lacosamide; LEV = levetiracetam; LTG = lamotrigine; mo = months; MRI = magnetic resonance imaging; MVD = moderate ventricular dilatation; NA = not available; OXC = oxcarbazepine; SE = status epilepticus; SS = spontaneous seizures; VGB = vigabatrin; VPA = valproic acid; y = years.

(n = 13/16) of the patients with truncating variants and in 33% (n = 1/3) of those with non-truncating variants.

## Reported Seizures Symptoms

The types of seizures, as reported by families and caregivers, were focal in 68% (n = 13) with possible secondary generalization in 58% (n = 11). Five patients were described as having generalized seizures (tonic-clonic [n = 4], myoclonic [n = 2], atonic [n = 1] and a behavioral arrest of

unknown origin in 1 patient). Autonomic manifestations were described in 11% of the individuals (n = 2), somatosensory manifestations in 5% (n = 1), behavioral arrest in 5% (n = 1), and impaired awareness in 16% (n = 3). Some descriptions were succinct, particularly for seizures in infants and children who cannot verbally express the sensations experienced during their seizures.

Altogether, 63% (n = 12/19) of the reported seizures presented a reflex component. Triggers were showering or
<table><caption>TABLE 3. Genetic, Clinical, Neurodevelopmental, and Epileptic Data, Patients XI-1 to XVI-1</caption><thead><tr><th>Patient</th><th>XI-1<sup>b</sup></th><th>XII-1<sup>b</sup></th><th>XIII-1</th><th>XIV-1<sup>a</sup></th><th>XV-1</th><th>XVI-1<sup>a,b</sup></th></tr></thead><tbody><tr><td>Age at the time of the study, gender</td><td>5 yr 6 mo, M</td><td>2 yr 6 mo, M</td><td>1 yr 9 mo, M</td><td>14 yr, M</td><td>13 yr, M</td><td>4 yr, M</td></tr><tr><td>City/country of collected data</td><td>Hamburg, Germany</td><td>Hamburg, Germany</td><td>Heeze, The Netherlands</td><td>Philadelphia/ Denmark</td><td>Toulouse, France</td><td>Nijmegen, The Netherlands</td></tr><tr><td>Mutation type</td><td>Frameshift</td><td>Frameshift</td><td>Frameshift</td><td>Frameshift</td><td>Inframe deletion</td><td>Frameshift</td></tr><tr><td>SYN1 variant, (NM_006950.3), inheritance</td><td>c.1472_1473insT; p. (Gln491Hisfs*193); Mat</td><td>c.1406dupA; p. (Pro470Alafs*214); Mat</td><td>c.1779dup; p. (Pro594ThrfsTer90); DN</td><td>c.39del; p.(Phe13Leufs*10); Mat</td><td>c.90_104del; p.Pro31-Pro35del; Mat</td><td>c.1647_1650dup; p.(Ser551fs); DN</td></tr><tr><td>Development - learning disabilities</td><td>Moderate ID</td><td>Mild ID, language delay</td><td>Language delay</td><td>Mild ID</td><td>Severe ID</td><td>Difficulty with pronunciation, language delay</td></tr><tr><td>Behavioral disturbances</td><td>ASD, ADHD</td><td>ADHD</td><td>No</td><td>Borderline behavior</td><td>ASD</td><td>ADHD, hypersensitivity</td></tr><tr><td>Neurological examination abnormalities</td><td>No</td><td>No</td><td>No</td><td>No</td><td>Hypertonia and hyperreflexia</td><td>No</td></tr><tr><td>Neuroimaging abnormalities (MRI)</td><td>No</td><td>No</td><td>No</td><td>Minor multicystic corpus pineal cyst</td><td>No</td><td>No</td></tr><tr><td>Age at seizure onset</td><td>4 yr 6 mo</td><td>2 yr</td><td>1 yr 6 mo</td><td>10 yr</td><td>2 yr</td><td>3 yr 6 mo</td></tr><tr><td>Suspected seizure type based on medical reports</td><td>Focal non motor autonomic with possible secondary GTCS</td><td>Focal with impaired awareness and possible secondary GTCS</td><td>Focal automatisms and impaired awareness with possible secondary GTCS</td><td>Focal autonomic onset with automatisms and impaired awareness</td><td>GTCS, atonic, myoclonic</td><td>Focal with possible secondary GTCS</td></tr><tr><td>Presence of reflex seizures/triggers</td><td>Yes/bathing and showering, haircutting, fingernail clipping, idea of bathing</td><td>Yes/bathing</td><td>No</td><td>Yes/toothbrushing, bathing and showering</td><td>No</td><td>No</td></tr><tr><td>SS, FS, and SE</td><td>SS and SE</td><td>SS</td><td>SS, FS, and SE</td><td>No</td><td>SS and FS</td><td>SS and SE</td></tr><tr><td>Frequency of seizures</td><td>2-8/mo</td><td>Weekly</td><td>Clustering when he is ill</td><td>1-2/mo</td><td>Stopped with treatment</td><td>Stopped with treatment</td></tr><tr><td>Current/previous antiseizure medications</td><td>VPA, LTG, STM</td><td>VPA</td><td>LEV, VPA/CBZ</td><td>ZNS, CBZ/ECB</td><td>VPA/TPM, CLB, LEV</td><td>LEV</td></tr><tr><td>Drug resistance</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Yes</td><td>No</td><td>No</td></tr><tr><td>Intertictal EEG</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Yes</td></tr><tr><td>Ictal EEG/number of seizures</td><td>Yes/3</td><td>No</td><td>No</td><td>No</td><td>No</td><td>No</td></tr></tbody></table>

ADHD = attention-deficit/hyperactivity disorder; ASD = autism spectrum disorder; CBZ = carbamazepine; CLB = clobazam; DN = de novo; ECB = eslicarbazepine; EEG = encephalographic; FS = febrile seizures; GTCS = generalized tonic-clonic seizures; ID = intellectual disability; LEV = levetiracetam; LTG = lamotrigine; M = male; Mat = maternal; mo = months; MRI = magnetic resonance imaging; TPM = topiramate; SE = status epilepticus; SS = spontaneous seizures; STM = sulthiame; VPA = valproic acid; yr = years.

bathing (n = 7), defecating (n = 2), emotions (n = 1), lightning strikes (n = 1), haircutting (n = 1), fingernail clipping (n = 1), the idea of bathing (n = 1), and toothbrushing (n = 1). Bathing reflex seizures were provoked by warm water in 3 patients and regardless

of the temperature of the water in 4 patients. The combination of provoked and unprovoked seizures was frequent during the course of epilepsy, present in 53% (n = 10) of the patients. Thirty-seven percent of the patients (n = 7) had only unprovoked seizures.
<figure><img src="image_4.png" /><figcaption>FIGURE 1: Graphical representation of intellectual disability, drug-resistance, truncating/non-truncating variant state and age at seizure onset in patients with SYN1-related epilepsy. [Color figure can be viewed at www.annalsofneurology.org]</figcaption></figure>

Thirty-two percent (n = 6) of the patients had a history of febrile seizures.

Fifty-eight percent of the patients (n = 11) proved to be drug-resistant; all had a truncating variant. The age at epilepsy onset was not predictive of response to antiseizure medications (p = 0.68, AUC = 44%, NS) and drug-resistance was not statistically associated with ID (p = 0.10, NS, Cochran–Armitage test). Learning disabilities or behavioral disturbances were found in 86% (n = 6) of patients who were seizure-free and in all other patients.

## Video-EEG Recorded Seizures

We analyzed the video-EEG data of 10 epileptic seizures recorded in 5 patients. For one patient (III-1), the seizure occurred while he was on the toilet (defecating), consequently the videotaping was not on, and the description was based on the nurse's report.

The clinical semiology of recorded seizures and EEG findings are summarized in Tables 4 to 7. The clinical sequence of events most frequently observed during seizures were associated orofacial automatisms (chewing), impaired awareness, and autonomic manifestations, such as pallor, cyanosis, or changes in cardiac rhythm. Orofacial automatisms were seen at the onset or occurred very early in 4 of 10 of the video-EEG recorded seizures.

The most commonly observed ictal symptoms were in descending order: orofacial automatisms in 70% (n = 7/10); upper limb dystonia or hypertonia in 50% (n = 5); apnea, cyanosis, or pallor in 40% (n = 4); eye blinking in 30% (n = 3); deviation of the head or the

eyes in 30% (n = 3); a fall in 10% (n = 1); and hemi-body hypomobility in 10% (n = 1). Secondary generalization was observed in only one patient (II-1). Tachycardia was present in all recorded seizures except for one (III-1 in seizure 1), in which bradycardia was observed (heart rate below 60 beats per minute for around 30 seconds compared with heart rate at 115 beats per minute prior to seizure onset), and associated with autonomic alterations, such as pallor, cyanosis, and apnea.

Triggers for video-EEG recorded seizures were cutaneous contact with water (n = 7), defecating (n = 2), photosensitive (n = 2), emotional (n = 1), toothbrushing (n = 1), haircutting (n = 1), fingernail clipping (n = 1), and the idea of bathing (n = 1).

For all seizures recorded, the EEG showed at onset a rhythmic theta followed by delta activity predominating in temporal or temporo-perisylvian regions (n = 8/10; see Fig 2) or in frontal regions (2/10), diffusing to the ipsilateral hemisphere, and sometimes bilaterally. It then frequently evolved into a rhythmic spike-waves activity in the same regions. Postictal hemispheric (n = 4) or diffuse (n = 1) slowing activity could be observed. In one patient (I-1), a short, fast, low voltage activity in the right temporal region could be distinguished, evolving toward a rhythmic theta/delta activity. We provide an EEG sample (centered on the onset of the seizure) of one seizure from each patient in whom at least one seizure could be recorded by video-EEG (Supplementary Data).

Overall, electro-clinical correlations showed that 80% (n = 8) of the seizures particularly involved the
<figure><img src="image_5.png" /><figcaption>FIGURE 2: EEG samples centered on the onset of the seizure 1 in patient I-1, with a rhythmic theta-delta activity on the right temporal region. Filters used: high-frequency filter 30 Hz and low-frequency filter 0.53 Hz. EEG = encephalographic; Hz = hertz. [Color figure can be viewed at www.annalsofneurology.org]</figcaption></figure>

temporo-mesial or temporo-insular regions. For one patient (IV-1), the 2 seizures recorded evoked a frontal region onset. Seventy percent (n = 7) of the seizures originated in the right hemisphere and 30% (n = 3) in the left. Two out of 5 patients experienced multifocal seizures. Patient I-1 had almost clinically similar seizures but of the right and left temporal origin. The right and left frontal seizures were recorded in patient IV-1.

## Interictal Descriptions

Interictal EEG analysis, both during wakefulness and sleep, were performed in all patients (n = 19; see Tables 4–7). The EEG background was normal in 17 patients (89%) and slow in 2 patients (11%). Slow waves were present in 4 patients, being focal in temporo-perisylvian regions in 3 and diffuse in 1 patient. No modification to photic stimulation or hyperpnea tests was identified. Physiologic sleep graphoelements were present and well organized for all patients, and less visible in only 1 patient.

Fifty-eight percent (n = 11) of the patients presented interictal paroxysmal graphoelements (spikes, spike-waves, or sharp waves). They were located mainly in the temporal (n = 4) or temporo-perisylvian regions (n = 6). In 1 patient, they were in the frontal region. A right hemispheric predominance was noted (n = 8). They were activated during sleep, becoming more frequent and sometimes spreading spatially to nearby regions. In 5 of the 11 patients with interictal paroxysmal graphoelements, they were rare (less than 1 per minute), so that 74% of

the patients (n = 14/19) had rare or non-visible interictal paroxysmal graphoelements.

## Video-EEG Psychogenic Non-Epileptic Seizures Description

PNES were recorded by video-EEG in 3 patients (16%) belonging to the same family (II-1, II-2, and II-3). The PNES could present clinical similarities with the semiology of associated epileptic seizures, albeit different. Patient II-1 had a PNES under the shower during video-EEG, presenting with atypical orofacial automatisms, impaired awareness, and a fall with no movement, no answer, and closed eyes, whereas the EEG did not record any abnormalities. Successive videos recorded in the same patient by his mother also showed very probable PNES with impaired consciousness, moderate hypersalivation, and agitation. Patient II-2 had 10 unprovoked PNES recorded by video-EEG with moderate disturbances of consciousness, forced eyes closure and blinking, head movements, and irregular/asynchronous generalized clonic movements. Patient II-3 had hypersalivation and chewing on video-EEG with a long duration and a possible memory recall of events during the episode, and no EEG modification. He also had numerous events at school with disturbed consciousness, blinking, and then closed eyes with no answer during several minutes.

## Electroencephalographic Power Spectrum Analysis

Nine patients with *SYNI* pathogenic variations were excluded from the interictal connectivity and power
<table><caption>TABLE 4. Ictal and Interictal EEG Analysis, Patients I-1, II-1, and III-1</caption><thead><tr><th>Patient</th><th>I-1<sup>a</sup></th><th>II-1<sup>a</sup></th><th>III-1</th></tr></thead><tbody><tr><td><strong>Awake interictal</strong></td><td></td><td></td><td></td></tr><tr><td>Background activity</td><td>Slow (theta)</td><td>Normal (alpha)</td><td>Normal (alpha)</td></tr><tr><td>Spatial organization</td><td>Correct</td><td>Correct</td><td>Correct</td></tr><tr><td>Paroxystic GE</td><td>Rare L T S</td><td>Rare R F-T S</td><td>No</td></tr><tr><td>Slow waves</td><td>Rare/L T</td><td>No</td><td>No</td></tr><tr><td>Photosensitivity</td><td>No</td><td>No</td><td>No</td></tr><tr><td><strong>Sleep interictal</strong></td><td></td><td></td><td></td></tr><tr><td>Physiologic GE during sleep</td><td>Yes</td><td>Yes</td><td>Yes</td></tr><tr><td>Paroxystic GE</td><td>Rare L T S</td><td>R F-T S</td><td>No</td></tr><tr><td>Slow waves</td><td>Rare/L T</td><td>No</td><td>No</td></tr><tr><td>Sleep S activation</td><td>No</td><td>Yes</td><td>No</td></tr><tr><td><strong>Recorded seizures</strong></td><td>1</td><td>2</td><td>3</td><td>1</td><td>1</td></tr><tr><td>Clinical description</td><td>OFA, then ipsilateral (L) eye blinking and impaired awareness, then R upper limb dystonia, post ictal confusion</td><td>OFA, then left moderate upper limb dystonia and cough</td><td>OFA and bilateral eye blinking, then bilateral upper limbs dystonia predominant on the R at last confusion</td><td>OFA and bad feeling, then rapid L eye blinking and repetitive R upper limb automatisms, at last secondary generalization</td><td>Impaired awareness during defecation, then R upper limb automatisms, OFA, hypersalivation, pallor/sweating, and fall</td></tr><tr><td>Ictal EEG description</td><td>Fast low voltage activity then rhythmic theta/delta activity in L T regions evolving in rhythmic SW. Then diffusion to both subsylvian regions. L post ictal slowing</td><td>Short fast low voltage activity then rhythmic theta/delta activity in R T regions evolving in rhythmic SW diffusing in the R hemisphere. R post ictal slowing</td><td>Rhythmic theta and delta activity in L T regions, then propagating in R T regions, after bilateral T rhythmic SW discharge. Diffuse post ictal slowing activity</td><td>Rhythmic theta activity in R T region evolving in R hemispheric rhythmic SW and then secondary generalization followed by global depression. R F-T post ictal slowing</td><td>R T-B rhythmic theta activity evolving to theta delta activity in bilateral F-T regions, predominant on the R hemisphere. R F-T post ictal slowing</td></tr><tr><td>ECG</td><td>Tachycardia</td><td>Tachycardia</td><td>Tachycardia</td><td>Tachycardia</td><td>Tachycardia</td></tr><tr><td>Seizure onset</td><td>L temporo-mesial</td><td>R temporo-mesial</td><td>L temporo-mesial</td><td>R temporo-mesial</td><td>R temporo-insular</td></tr></tbody></table>

B = basal; C = central; EEG = encephalographic; F = frontal; GE = grapho-element; L = left; O = occipital; OFA = oro-facial automatisms; R = right; S = spike; SW = spike waves; T = temporal.

spectrum analysis because some of their electrodes con- tained too many artifacts or were missing (n = 1, patient XV-1) so it was not possible to compare them

to the healthy subjects, or because they were younger than 12 years old (n = 8). No major differences were observed between patients under and over the age of

<footnote><sup>a</sup>Refers to patients yet published in the following article: Parenti I, Leitão E, Kuechler A, et al. The different clinical facets of SYN1-related neu- rodevelopmental disorders. Front Cell Dev Biol 2022; 10: 1019715.</footnote>

<footnote><sup>b</sup>Refers to patients yet published in the following article: Accogli A, Wiegand G, Scala M, et al. Clinical and Genetic Features in Patients With Reflex Bathing Epilepsy. Neurology 2021; 97 (6): e577-e586.</footnote>
<table><caption>TABLE 5. Ictal and Interictal EEG Analysis, Patients IV-1 and XI-1</caption><thead><tr><th>Patient</th><th>IV-1<sup>a</sup></th><th>XI-1<sup>b</sup></th></tr></thead><tbody><tr><td><strong>Awake interictal</strong></td><td></td><td></td></tr><tr><td>Background activity</td><td>Normal (alpha)</td><td>Normal (alpha)</td></tr><tr><td>Spatial organization</td><td>Diffusing</td><td>Correct</td></tr><tr><td>Paroxystic GE</td><td>BiT asynchronous S, SW</td><td>Frequent R T SW</td></tr><tr><td>Slow waves</td><td>No</td><td>No</td></tr><tr><td>Photosensitivity</td><td>No</td><td>No</td></tr><tr><td><strong>Sleep interictal</strong></td><td></td><td></td></tr><tr><td>Physiologic GE during sleep</td><td>Yes</td><td>Yes</td></tr><tr><td>Paroxystic GE</td><td>BiT asynchronous S, SW</td><td>Frequent and ample R T S and SW</td></tr><tr><td>Slow waves</td><td>No</td><td>No</td></tr><tr><td>Sleep S activation</td><td>Yes</td><td>Yes</td></tr><tr><th>Recorded seizures</th><th>1</th><th>2</th><th>1</th><th>2</th><th>3</th></tr><tr><td>Clinical description</td><td>Slow L deviation of head/eyes, then upper limbs hypertonia and L clonic head deviation and L upper limb clonies</td><td>Left gaze deviation, then bilateral crispation of the corners of the mouth. At last R hemibody hypomobility</td><td>Asymptomatic for 1 min while bathing, then pallor, apnea, cyanosis and no response, at last L head/eyes deviation</td><td>Chills and cyanosis after bathing, then difficulty to answer questions and OFAs</td><td>Impaired awareness during bathing, cyanosis/OFA, head/ limbs hypotonia, then shoulders hypertonia and cough</td></tr><tr><td>Ictal EEG description</td><td>BiF rhythmic theta activity (predominating in R F region) and then secondary generalization</td><td>Rhythmic theta-delta activity in L central region evolving rhythmic SW in L T region</td><td>R C-T sharp waves, then R C-T theta rhythmic activity second diffusing, at last diffuse depression of EEG activity</td><td>Diffuse rhythmic theta activity, predominantly in R F-T region, then diffuse rhythmic high amplitude delta activity</td><td>Enhancement of interictal R T SW, then theta rhythmic activity in R T region evolving to rhythmic SW activity in R hemisphere and then in both hemispheres</td></tr><tr><td>ECG</td><td>Tachycardia</td><td>Tachycardia</td><td>Bradycardia</td><td>Tachycardia</td><td>Tachycardia</td></tr><tr><td>Seizure onset</td><td>R frontal</td><td>L frontal</td><td>R temporo-insular</td><td>R fronto-temporal</td><td>R temporal</td></tr></tbody><tfoot><tr><td colspan="6">BiF = Bi-frontal; BiT = Bi-temporal; C = central; EEG = encephalographic; F = frontal; GE = grapho-element; L = left; O = occipital; OFA = oro-facial automatisms; R = right; S = spike; SW = spike waves; T = temporal.</td></tr></tfoot></table>

12 years, in terms of epileptic characteristics or com-orbidities (Fig 2).

For healthy subjects, a strong occipital alpha peak at 10 Hz was found, whereas patients with *SYNI* variants (n = 10) had less power in the alpha band (Fig 3). A stronger predominance of the theta and delta frequency bands relatively to the alpha power-band in patients was also visually observed. These results are therefore in favor

of a slower EEG rhythm in patients with *SYNI* pathogenic variations.

### Electroencephalographic Connectivity Analysis

In healthy subjects, we observed a strong resting-state PLV connectivity in the frontal and occipital regions, with long distance connectivity links between these 2 regions identified. However, for patients with *SYNI* variants (n = 10), the
<table><caption>TABLE 6. Ictal and Interictal EEG Analysis, Patients II-2, II-3, V-1, VI-1, VII-1, VIII-1, and VIII-2</caption><thead><tr><th>Patient</th><th>IX-1</th><th>X-1</th><th>XII-1<sup>b</sup></th><th>XIII-1</th><th>XIV-1<sup>a</sup></th><th>XV-1</th><th>XVI-1<sup>a,b</sup></th></tr></thead><tbody><tr><td>Awake interictal</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Background activity</td><td>Normal (alpha)</td><td>Normal (alpha)</td><td>Normal (alpha)</td><td>Normal (theta-alpha)</td><td>Normal (alpha)</td><td>Normal (alpha)</td><td>Normal (alpha)</td></tr><tr><td>Spatial organization</td><td>Correct</td><td>Correct</td><td>Correct</td><td>Correct</td><td>Correct</td><td>Correct</td><td>Correct</td></tr><tr><td>Paroxystic GE</td><td>Rare R F-C-T S and SW</td><td>R F S</td><td>No</td><td>No</td><td>No</td><td>No</td><td>No</td></tr><tr><td>Slow waves</td><td>No</td><td>No</td><td>No</td><td>Yes/L hemisphere with C-T predominance</td><td>No</td><td>Yes/diffuse</td><td>No</td></tr><tr><td>Photosensitivity</td><td>No</td><td>No</td><td>No</td><td>No</td><td>No</td><td>No</td><td>No</td></tr><tr><td>Sleep interictal</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Physiologic GE during sleep</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Less visible on L hemisphere</td><td>Yes</td><td>Yes</td><td>Yes</td></tr><tr><td>Paroxystic GE</td><td>R F S and SW</td><td>R F-T S</td><td>BiT S and SW</td><td>No</td><td>No</td><td>Bilateral multifocal rare slow SW</td><td>BiF sharp waves</td></tr><tr><td>Slow waves</td><td>No</td><td>No</td><td>No</td><td>Yes/L hemisphere with F-C predominance</td><td>No</td><td>No</td><td>No</td></tr><tr><td>Sleep S activation</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Yes</td><td>No</td><td>Yes</td><td>Yes</td></tr><tr><td>Seizure recorded</td><td><strong>No</strong></td><td><strong>No</strong></td><td><strong>No</strong></td><td><strong>No</strong></td><td><strong>No</strong></td><td><strong>No</strong></td><td><strong>No</strong></td></tr></tbody></table>

BiF = Bi-frontal; C = central; EEG = encephalographic; F = frontal; GE = grapho-element; L = left; R = right; S = spike; SW = spike waves; T = temporal.

connectivity map was different, with the strongest connectivity links in both temporal regions (Fig 4). Two connectivity metrics were computed for each group: the clustering coefficient and the path length. Path length appeared to be similar, but a lower clustering coefficient was observed in patients with *SYNI* variants compared to healthy control individuals (Fig 5).

Discussion

We analyzed video-EEG data of 10 epileptic seizures in 5 patients and interictal EEG data of 19 patients. To our knowledge, this is the largest reported cohort of patients with epilepsy related to *SYNI* variants with detailed

clinical and electrophysiological data. Based on the observation of shared clinical and EEG features among patients with *SYNI*-related epilepsy we suggest the delineation of a distinct epilepsy syndrome. Indeed, 80% of the seizures (8/10) recorded in video-EEG involved the temporal or temporo-insular/perisylvian regions. Ictal semiology consisted mostly of impaired awareness, automatisms, and autonomic symptoms. Ictal EEG showed a characteristic rhythmic theta/delta activity predominating in temporal or temporo-perisylvian regions at the beginning of most of the seizures. Only one patient (2 seizures) presented with electroclinical data evoking frontal lobe seizures.

To date, published data on electro-clinical patterns of seizures in patients with *SYNI* pathogenic variations is
<table><caption>TABLE 7. Ictal and Interictal EEG Analysis, Patients IX-1, X-1, XII-1, XIII-1, XIV-1, XV-1, and XVI-1</caption><thead><tr><th>Patient</th><th>II-2<sup>a</sup></th><th>II-3<sup>a</sup></th><th>V-1<sup>a</sup></th><th>VI-1<sup>a</sup></th><th>VII-1<sup>a</sup></th><th>VIII-1<sup>a</sup></th><th>VIII-2<sup>a</sup></th></tr></thead><tbody><tr><td>Awake interictal</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Background activity</td><td>Normal (alpha)</td><td>Normal (alpha)</td><td>Normal (alpha)</td><td>Normal (alpha)</td><td>Slow (theta-alpha)</td><td>Normal (alpha)</td><td>Normal (alpha)</td></tr><tr><td>Spatial organization</td><td>Correct</td><td>Correct</td><td>Correct</td><td>Correct</td><td>Diffusing</td><td>Correct</td><td>Correct</td></tr><tr><td>Paroxystic GE</td><td>R F-T SW and rare sharp waves</td><td>R F-C-T SW</td><td>Rare R T sharp waves</td><td>R F-T SW and sharp waves</td><td>No</td><td>L T-O SW</td><td>No</td></tr><tr><td>Slow waves</td><td>No</td><td>No</td><td>No</td><td>No</td><td>No</td><td>Yes/L T-O</td><td>No</td></tr><tr><td>Photosensitivity</td><td>No</td><td>No</td><td>No</td><td>No</td><td>No</td><td>No</td><td>No</td></tr><tr><td>Sleep interictal</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Physiologic GE during sleep</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Yes</td></tr><tr><td>Paroxystic GE</td><td>R F-T S</td><td>No</td><td>No</td><td>R F-T SW and sharp waves</td><td>No</td><td>No</td><td>No</td></tr><tr><td>Slow waves</td><td>No</td><td>No</td><td>No</td><td>No</td><td>No</td><td>No</td><td>No</td></tr><tr><td>Sleep S activation</td><td>Yes</td><td>No</td><td>No</td><td>Yes</td><td>No</td><td>No</td><td>No</td></tr><tr><td>Seizure recorded</td><td>No</td><td>No</td><td>No</td><td>No</td><td>No</td><td>No</td><td>No</td></tr></tbody></table>

C = central; EEG = encephalographic; F = frontal; GE = grapho-element; L = left; O = occipital; R = right; SW = spike waves; T = temporal.

<figure><img src="image_6.png" /><figcaption>FIGURE 3: Electroencephalographic interictal occipital (O1–O2) power spectrum frequency analysis, ±2 standard deviations. [Color figure can be viewed at www.annalsofneurology.org]</figcaption></figure>

rather scarce. A first publication in 2015⁵ described 2 patients recorded with continuous video-EEG monitoring. The first patient was a 50-year-old man who presented 3 stereotypical seizures provoked by rubbing of his face with a wet cloth characterized by an aura of body chill, alteration of consciousness, manual automatisms, and rare secondary generalized tonic-clonic activity. Ictal EEG revealed an ictal right temporal rhythmic theta activity with subsequent propagation. The second patient was a 17-year-old boy who presented by bathing or nail clipping reflex seizures with focal temporal clinical onset. Ictal EEG disclosed rhythmic delta activity over the right temporal regions that quickly spread to parasagittal regions and evolved into a rhythmic spike and slow wave pattern. Sirsi et al²⁵ reported 2 seizures recorded in video-EEG in a 7-year-old boy, triggered by contact with water. The electrographic seizure mainly evolved over the left temporal region. During the second seizure, ictal evolution was in the right fronto-temporal region. Ameen et al²⁶ described a 6-year-old boy who presented water-reflex seizures with focal onset characterized by autonomic symptoms, mouth
<figure><img src="image_7.png" /><figcaption>FIGURE 4: Phase locking value functional connectivity metric at 10 Hz (links weaker than 1 standard deviation are not shown). Hz = hertz. [Color figure can be viewed at www.annalsofneurology.org]</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>FIGURE 5: Weighted clustering coefficient (from 0 to 1) and average path length (from 0 to 1). [Color figure can be viewed at www.annalsofneurology.org]</figcaption></figure>

automatisms, and impaired awareness. Ictal EEG from an ambulatory home EEG, showed a rhythmic theta activity arising from the left fronto-temporal area. Peron et al¹⁰ reported focal seizures during contact with water in an 8-year-old patient. They were characterized by a sensation of rising heat, hemi-body dystonic posture, and cyanosis of the lips, followed by oral automatisms and inability to speak. Ictal EEG showed bilateral rhythmic theta activity over the fronto-central regions. Finally, Accogli et al¹⁵ reported 2 patients with bathing reflex autonomic seizures. Ictal EEG showed high-voltage polymorphic theta activity over the fronto-temporal areas.

All these case reports provide data which are rather consistent with our own, pointing to focal seizures originating or propagating rapidly to the temporal or temporo-insular/perisylvian regions. Autonomic ictal manifestations were

frequently reported, in particular apnea, cyanosis or changes in cardiac rhythm, sometimes in the foreground. This finding also suggests involvement of temporal or temporo-perisylvian regions, in which cardiac changes are more frequently reported than in extra-temporal seizures.⁴⁰ We found a right-hemisphere predominance in seizure organization, raising the question of possible hemispheric specialization. Indeed, some studies using intracerebral stimulations or neuroimaging have suggested that the right cerebral hemisphere is potentially more involved in sympathetic functions, and the left in parasympathetic functions, but more recent studies involving larger numbers of patients have not confirmed this hypothesis.⁴¹⁻⁴⁴ Moreover, looking at the video-EEG cases reported in the literature, we do not find this preferential right-hemispheric lateralization of seizures. Of the 7 patients reported, 3 have seizures starting on the right hemisphere, 3 on the left, and 1 bilaterally.⁵,¹⁰,¹⁵,²⁵,²⁶ Thus, despite the right predominance of seizures' organization in our data, the relatively small number of patients should make these data on lateralization taken with caution and further studies, including a larger numbers of patients, should clarify this point.

Moreover, the high prevalence of oro-facial automatisms at the onset of the recorded video-EEG seizures suggests likewise the involvement of temporo-mesial and insular regions in the genesis of these seizures.⁴⁵,⁴⁶

Intertictal paroxysmal graphoelements (such as spikes or spike-waves) were rare or absent in almost 70% of our patients (n = 13/19), and, when present, tended to be localized in the temporo-perisylvian regions. This is compatible
or even suggestive of a deep seizure onset, possibly in the temporal or insular regions. Similarly, an ictal EEG pattern was also evocative, with rhythmic theta activity at the onset of most seizures, followed by delta activity predominating in the temporal or temporo-perisylvian regions, diffusing into the ipsilateral hemisphere, and sometimes bilaterally. This pattern also reported in the few patients with *SYN1*-related epilepsy who benefited from a video-EEG recording,⁵,¹⁵,²⁵ is also consistent with a deeply localized seizure onset, having similarities with what has been reported in mesial temporal seizures.⁴⁷,⁴⁸

This electroclinical pattern of focal seizures, involving mainly the temporo-insulo/perisylvian regions, is somewhat different from what one could expect when based on seizure descriptions reported by caregivers and parents. Although focal seizures are mentioned, seizures with prominent motor manifestations or seizures with a generalized appearance are frequently reported,²¹ probably because they are easier to identify. It is likely that some manifestations of focal seizures go unnoticed because they are either subtle, or can only be reported subjectively, which is impossible in young children or patients who cannot verbally express their sensations. This highlights the importance of video-EEG recordings to gather accurate electro-clinical information to support the choice of the most appropriate antiseizure medications and to provide more data about the pathogenesis of this epilepsy syndrome.

Moreover, we recorded PNES on video-EEG in 3 of our patients. It is likely that the frequency of PNES in patients with *SYN1*-related epilepsy remains underestimated. Especially if, as in our patients, some PNES are triggered by cutaneous contact with water, also having clinical similarities with the truly epileptic paroxysmal events. Video-EEG recordings are therefore also important for identifying PNES to avoid unnecessary modifications in antiseizure medications. Genetic variants associated to neurologic disorders may be a potential hypothesis to explain the high frequency of PNES occurring in this epilepsy syndrome.⁴⁹

We observed a more important proportion of ID in the patients with an epileptic seizure onset before the age of 5 years, but we did not find a link between the severity of epilepsy and cognitive/behavioral impairment. It suggests that cognitive impairment processes are not the sole consequence of epileptic seizures but are most likely also related to parallel pathophysiological processes resulting from the *SYN1* gene alteration. Similarly, Parenti et al (2022)²¹ did not detect enrichment in developmental delay, ID, or ASD in patients with epilepsy compared with non-epileptic patients, although they noted an association between a younger age at seizure onset and the

severity of ID, and the loss of acquired milestones for some individuals after the onset of seizures. Neurological features of some patients, but not all, with *SYN1* variants seem therefore to correspond to a developmental and epileptic encephalopathy, as a part of developmental difficulties seem to be arising directly from the effect of the genetic mutation, with an additional effect of the epileptic activity on development.⁵⁰ The shift toward slower frequency bands of interictal EEG observed in patients with *SYN1* variants compared to healthy subjects has also been described in neurodevelopmental disorders, such as ADHD.⁵¹,⁵² However, no statistical analysis could be performed in our study because of the small group size.

Epilepsy usually begins in childhood and seizures often persist through adult life, with possible drug-resistance. A very particular clinical feature is the appearance of reflex seizures, which, in our series, occurred in 63% of patients. This appears to be in line with previously published data, as several triggers have been reported in individual patients with *SYN1* variants, initially and mainly water-related, such as showering or bathing, but also rubbing with a towel, cutting hair, clipping nails, the thought of taking a bath, brushing teeth, defecating, and laughing.¹⁵,²⁰,²¹,²⁵,²⁶ Reflex epilepsy can be defined as the presence of recurrent seizures in response to a specific motor, sensory, or cognitive stimulation.⁵³⁻⁵⁵ Exact pathophysiological mechanisms remain unknown but probably include a hyper-excitability of cortical or subcortical neuronal areas in response to a physiologic stimulus. It is noteworthy that most of the triggers reported in SYN1-related epilepsy correspond to somatosensory stimuli. Most patients have a single reproducible trigger for their seizures. Interestingly, some patients showed a more heterogeneous sensitivity to various triggers (such as cutaneous contact with water and toothbrushing; or cutaneous contact with water, haircutting, and fingernail clipping), raising the question of possibly different pathophysiologic mechanisms. However, it is noticeable that (except for 2 patients, who had a visual trigger), all the triggers are somato-sensory and body-centered and so probably involve the same somatosensory networks. This is consistent with the description of temporo-insular seizures we report in our patients, as the insula is one of the most important brain areas for the processing of somatosensory and thermal stimuli, particularly in its medium/posterior part.⁵⁶ Somatosensory physiological stimuli, such as cutaneous contact with water, could thus trigger seizures by activating genetically based hyperexcitable temporo-insular networks.

This is consistent with the increased connectivity in both temporo-perisylvian regions we visually found in patients with *SYN1* variants compared with healthy subjects. Our findings suggest a reorganization of
networks, and could support a hyperexcitability of
these regions, perhaps at the origin of the onset of sei-
zures in these patients.<sup>27,29,30,32</sup>

Our study comprehensively defined the electroclinical
features of epilepsy in patients with *SYN1* pathogenic vari-
ants. A distinct epilepsy syndrome emerged, the phenotype
of which can be described as follows: (1) EEG background
and organization are mainly normal or slightly slow, in wake-
fulness and sleep; (2) interictal abnormalities are often rare or
not visible on EEG; when visible, they mostly consist of
spikes or spike-waves in temporal or temporo-perisylvian
regions; (3) more than 60% of patients have reflex seizures
(cutaneous contact with water and defecation being the main
triggers) isolated or associated with spontaneous seizures;
(4) electro-clinical semiology of seizures is mainly temporal
or temporo-insulo/perisylvian with a notable autonomic
component; and (5) ictal EEG shows a characteristic
rhythmic theta/delta activity predominating in temporal
or temporo-perisylvian regions at the beginning of most
seizures. The association of the above in features in chil-
dren with (or without) neurodevelopmental or behavioral
difficulties should help to guide genetic diagnosis and
facilitate the identification of new families sharing the
same genetic condition.

## Acknowledgments

The authors thank the networks ERN EpiCARE (European Reference Network for rare and complex epilepsies) and LFCE (French League Against Epilepsy) by announcements, for increasing the number of patients included in this study, and all individuals, including patients and their families, who participated in the study, as well as the clinicians, researchers, and nursing staff of all institutions that contributed to the investigations.

## Author Contributions

V.M.Q., A.Ad., and L.M. contributed to the conception and design of the study. V.M.Q., A.Ad., H.S., A.Ar., P. Co., G.L., F.M., A.B., H.B., J.P.C., P.Ca., L.C., Y.C., M.C., C.D., V.De., J.D.R., V.Di., E.G., G.J.K., J.J., M.L.M., M.M.M., M.M., A.L.P., K.P., A.R., M.F.S., A.T.V.S., G.W., and L.M. contributed to the acquisition and analysis of data. V.M.Q., A.Ad., and L.M. contributed to drafting the text and preparing the figures.

## Potential Conflicts of Interest

Nothing to report.

## Data Availability

The data that support the findings of this study are
available on request from the corresponding authors
V.M.Q. and L.M.

## References

1. Cesca F, Baldelli P, Valtorta F, Benfenati F. The synapsins: key actors of synapse function and plasticity. Prog Neurobiol 2010;91:313-348.

2. Guamieri FC, Pozzi D, Raimondi A, et al. A novel SYN1 missense mutation in non-syndromic X-linked intellectual disability affects synaptic vesicle life cycle, clustering and mobility. Hum Mol Genet 2017;26:4699-4714.

3. Garcia CC, Blair HJ, Seager M, et al. Identification of a mutation in synapsin I, a synaptic vesicle protein, in a family with epilepsy. J Med Genet 2004;41:183-186.

4. Fassio A, Patry L, Congia S, et al. SYN1 loss-of-function mutations in autism and partial epilepsy cause impaired synaptic function. Hum Mol Genet 2011;20:2297-2307.

5. Nguyen DK, Rouleau I, Sénéchal G, et al. X-linked focal epilepsy with reflex bathing seizures: characterization of a distinct epileptic syndrome. Epilepsia 2015;56:1098-1108.

6. Butler KM, da Silva C, Alexander JJ, et al. Diagnostic yield from 339 epilepsy patients screened on a clinical gene panel. Pediatr Neurol 2017;77:61-66.

7. Rossi M, El-Khechen D, Black MH, et al. Outcomes of diagnostic exome sequencing in patients with diagnosed or suspected autism Spectrum disorders. Pediatr Neurol 2017;70:34-43.e2.

8. Cabana J-F, Gilbert G, Letourneau-Guillon L, et al. Effects of SYN1Q555X mutation on cortical gray matter microstructure. Hum Brain Mapp 2017;39:3428-3448.

9. Lindy AS, Stosser MB, Butler E, et al. Diagnostic outcomes for genetic testing of 70 genes in 8565 patients with epilepsy and neurodevelopmental disorders. Epilepsia 2018;59:1062-1071.

10. Peron A, Baratang NV, Canevini MP, et al. Hot water epilepsy and SYN1 variants. Epilepsia 2018;59:2162-2163.

11. Fernández-Marmiesse A, Roca I, Díaz-Flores F, et al. Rare variants in 48 genes account for 42% of cases of epilepsy with or without neurodevelopmental delay in 246 pediatric patients. Front Neurosci 2019;13:1135.

12. Darvish H, Azcona LJ, Tafakhori A, et al. Phenotypic and genotypic characterization of families with complex intellectual disability identified pathogenic genetic variations in known and novel disease genes. Sci Rep 2020;10:968.

13. Ibarluzea N, de la Hoz AB, Villate O, et al. Targeted next-generation sequencing in patients with suggestive X-linked intellectual disability. Genes 2020;11:51.

14. Yang JO, Choi M-H, Yoon J-Y, et al. Characteristics of genetic variations associated with Lennox-Gastaut syndrome in Korean families. Front Genet 2020;11:590924.

15. Accogli A, Wiegand G, Scala M, et al. Clinical and genetic features in patients with reflex bathing epilepsy. Neurology 2021;97:e577-e586.

16. Mojarad BA, Yin Y, Manshaei R, et al. Genome sequencing broadens the range of contributing variants with clinical implications in schizophrenia. Transl Psychiatry 2021;11:84.

17. Stranneheim H, Lagerstedt-Robinson K, Magnusson M, et al. Integration of whole genome sequencing into a healthcare setting: high diagnostic rates across multiple clinical entities in 3219 rare disease patients. Genome Med 2021;13:40.
18. van der Ven AT, Johannsen J, Kortüm F, et al. Prevalence and clinical prediction of mitochondrial disorders in a large neuropediatric cohort. Clin Genet 2021;100:766-770.

19. Xiong J, Duan H, Chen S, et al. Familial SYN1 variants related neurodevelopmental disorders in Asian pediatric patients. BMC Med Genomics 2021;14:182.

20. Zhou Q, Wang J, Xia L, et al. SYN1 mutation causes X-linked Tooth-brushing epilepsy in a Chinese family. Front Neurol 2021;12.

21. Parenti I, Leitão E, Kuechler A, et al. The different clinical facets of SYN1-related neurodevelopmental disorders. Front Cell Dev Biol 2022;10:1019715.

22. Leuschner UV, Kleinle S, Holzinger A, Neef J. Novel SYN1 variant in two brothers with focal epilepsy and their prompt response to valproate. Neuropediatrics 2023;54:206-210.

23. John A, Ng-Cordell E, Hanna N, et al. The neurodevelopmental spectrum of synaptic vesicle cycling disorders. J Neurochem 2021; 157:208-228.

24. Longhena F, Faustini G, Brembati V, et al. An updated reappraisal of synapsins: structure, function and role in neurological and psychiatric disorders. Neurosci Biobehav Rev 2021;130:33-60.

25. Sirsi D, Armstrong D, Muñoz-Bibiloni J, et al. SYN1 gene mutation in a child with focal epilepsy and reflex bathing seizures. J Pediatr Epilepsy 2017;6:6-124.

26. Ameen RB, Barker L, Zafar MS. Electroencephalography findings in bathing reflex epilepsy. Pediatr Neurol 2020;102:81.

27. Luo C, An D, Yao D, Gotman J. Patient-specific connectivity pattern of epileptic network in frontal lobe epilepsy. Neuroimage Clin 2014; 4:668-675.

28. Vecchio F, Miraglia F, Curcio G, et al. Cortical connectivity in fronto-temporal focal epilepsy from EEG analysis: a study via graph theory. Clin Neurophysiol 2015;126:1108-1116.

29. Clemens B, Puskás S, Spisák T, et al. Increased resting-state EEG functional connectivity in benign childhood epilepsy with centro-temporal spikes. Seizure 2016;35:50-55.

30. Englot DJ, Konrad PE, Morgan VL. Regional and global connectivity disturbances in focal epilepsy, related neurocognitive sequelae, and potential mechanistic underpinnings. Epilepsia 2016;57:1546-1557.

31. Scally B, Burke MR, Bunce D, Delvenne J-F. Resting-state EEG power and connectivity are associated with alpha peak frequency slowing in healthy aging. Neurobiol Aging 2018;71:149-155.

32. Lagarde S, Bénar C-G, Wendling F, Bartolomei F. Interictal functional connectivity in focal refractory epilepsies investigated by intracranial EEG. Brain Connect 2022;12:850-869.

33. Chung YG, Jeon Y, Kim RG, et al. Variations of resting-state EEG-based functional networks in brain maturation from early childhood to adolescence. J Clin Neurol 2022;18:581-593.

34. Chouchou F, Bouet R, Pichot V, et al. The neural bases of ictal tachycardia in temporal lobe seizures. Clin Neurophysiol 2017;128: 1810-1819.

35. Dong L, Li F, Liu Q, et al. MATLAB toolboxes for reference electrode standardization technique (REST) of scalp EEG. Front Neurosci 2017;11.

36. van Diessen E, Zweiphenning WJEM, Jansen FE, et al. Brain network Organization in Focal Epilepsy: a systematic review and meta-analysis. PLoS One 2014;9:e114606.

37. Bartolomei F, Lagarde S, Wendling F, et al. Defining epileptogenic networks: contribution of SEEG and signal analysis. Epilepsia 2017; 58:1131-1147.

38. Rubinov M, Knock SA, Stam CJ, et al. Small-world properties of nonlinear brain activity in schizophrenia. Hum Brain Mapp 2009;30: 403-416.

39. Rubinov M, Sporns O. Complex network measures of brain connectivity: uses and interpretations. Neuroimage 2010;52:1059-1069.

40. Mazzola L, Rheims S. Ictal and Interictal cardiac manifestations in epilepsy. A review of their relation with an altered central control of autonomic functions and with the risk of SUDEP. Front Neurol 2021; 12:642645.

41. Beissner F, Meissner K, Bär K-J, Napadow V. The autonomic brain: An activation likelihood estimation meta-analysis for central processing of autonomic function. J Neurosci 2013;33:10503-10511.

42. Chouchou F, Mauguière F, Vallayer O, et al. How the insula speaks to the heart: cardiac responses to insular stimulation in humans. Hum Brain Mapp 2019;40:2611-2622.

43. Sanchez-Larsen A, Principe A, Ley M, et al. Characterization of the insular role in cardiac function through intracranial electrical stimulation of the human insula. Ann Neurol 2021;89:1172-1180.

44. Ferraro S, Klugah-Brown B, Tench CR, et al. Dysregulated anterior insula reactivity as robust functional biomarker for chronic pain—meta-analytic evidence from neuroimaging studies. Hum Brain Mapp 2021;43:998-1010.

45. Maillard L, Vignal J-P, Gavaret M, et al. Semiologic and Electrophysiologic correlations in temporal lobe seizure subtypes. Epilepsia 2004;45:1590-1599.

46. Aupy J, Noviawaty I, Krishnan B, et al. Insulo-opercular cortex generates oroalimentary automatisms in temporal seizures. Epilepsia 2018; 59:583-594.

47. Dericioglu N, Saygi S. Ictal scalp EEG findings in patients with mesial temporal lobe epilepsy. Clin EEG Neurosci 2008;39:20-27.

48. Landazuri P. Mesial temporal lobe epilepsy: a distinct electroclinical subtype of temporal lobe epilepsy. Neurodiagn J 2014;54:274-288.

49. Leu C, Bautista JF, Sudarsanam M, et al. Neurological disorder-associated genetic variants in individuals with psychogenic non-epileptic seizures. Sci Rep 2020;10:15205.

50. Scheffer IE, Berkovic S, Capovilla G, et al. ILAE classification of the epilepsies: position paper of the ILAE Commission for Classification and Terminology. Epilepsia 2017;58:512-521.

51. Barry RJ, Clarke AR, Johnstone SJ. A review of electrophysiology in attention-deficit/hyperactivity disorder: I. Qualitative and quantitative electroencephalography. Clin Neurophysiol 2003;114:171-183.

52. Snyder SM, Hall JR. A meta-analysis of quantitative EEG power associated with attention-deficit hyperactivity disorder. J Clin Neurophysiol 2006;23:440-455.

53. Xue LY, Ritaccio AL. Reflex seizures and reflex epilepsy. Am J Electroneurodiagnostic Technol 2006;46:39-48.

54. Wolf P, Koepp M. Reflex epilepsies [Internet]. In: Stefan H, Theodore WH, eds. Handbook of Clinical Neurology. Elsevier, 2012; Chapter 16:257-276.

55. Okudan ZV, Özkara Ç. Reflex epilepsy: triggers and management strategies. Neuropsychiatr Dis Treat 2018;14:327-337.

56. Mazzola L, Royet J-P, Catenois H, et al. Gustatory and olfactory responses to stimulation of the human insula. Ann Neurol 2017;82: 360-370.