Natural History Study in Pediatric Patients with STXBP1 Encephalopathy with Epilepsy

Inclusion Criteria: * Male or female, \> 1 day to ≤ 5 years of age at the time of informed consent. * Diagnosed with seizure disorder * Presence of a STXBP1 gene mutation. Historical documentation is sufficient to support eligibility for the study. Confirmatory testing will be obtained at baseline and performed by a CLIA certified laboratory * Written informed consent provided by a parent or legal guardian Exclusion Criteria: * History of prior gene therapy treatment * Current enrollment in an interventional study or has received an investigational drug within 30 days or fewer than 5 half-lives prior to screening visit, whichever is longer * Treatment with any antisense oligonucleotide therapy within 6 months prior to screening and anticipate remaining on treatment throughout the study * The presence of a confirmed mutation in a gene other than STXPB1 that is known to contribute to a neurodevelopmental disability * Presence of a significant non-STXBP1 related central nervous impairment/behavioral disturbance that would confound the scientific rigor or interpretation of results of the study * History of prematurity (defined as gestational age \<35 weeks), interventricular hemorrhage, structural brain deficit or congenital heart disease * Requires mechanical ventilation or non-invasive respiratory support such as continuous positive airway pressure (CPAP) or bilevel positive airway pressure (BiPAP) at the time of informed consent