Longitudinal Study of Phenotypic and Developmental Severity in Patients With Dravet Syndrome With SCN1A Gene Mutation

Inclusion Criteria: * The patient or his/her legal representative must be able to give informed consent for participation in the study. * The participant or legal representative are able (in the opinion of the investigator) to comply with the research protocol. * Patient (male/female) between 6 months and 21 years of age inclusive at the time of consent. * The patient has a confirmed pathogenic or probably pathogenic variant of the SCN1A gene demonstrated by a genetic test. * The patient had normal development prior to the onset of the first seizure. * The patient had an onset of epileptic seizures between the ages of 3 and 15 months inclusive. * The patient is receiving at least one of the following anti-epileptic drugs prior to consent: brivaracetam, clobazam, cannabidiol, fenfluramine, levetiracetam, sodium valproate, stiripentol, topiramate Exclusion Criteria: * The patient has a copy number variation of the SCN1A gene affecting other genes, including a microdeletion of SCN1A. * The patient has a mutation in the SCN1A gene on both alleles. * The patient has a known or clinically suspected pathogenic mutation in a gene associated with epilepsy other than the SCN1A gene. * The patient has a concomitant genetic mutation or clinical comorbidity deemed likely to disrupt the typical phenotype of Dravet syndrome. * The patient has a known gain-of-function mutation, defined by functional studies, including p.Thr226Met. * The patient has a history of neurodevelopmental abnormality prior to the onset of seizures, based on the medical record. * The patient has been seizure free for a period of one year prior to informed consent. * The patient has, at any time, taken antiepileptic drugs with a worsening effect for 6 consecutive weeks or more, including: carbamazepine, eslicarbazepine, lacosamide, lamotrigine, oxcarbazepine, phenytoin (chronic oral administration), tiagabine and vigabatrin. * The patient has already received innovative therapies such as antisense ologonucleotides, gene therapy or cell therapy. * The patient has a structural abnormality on brain imaging (MRI or CT scan) which the principal investigator considers to be an epileptogenic lesion.