Influence of age at seizure onset on the acquisition of neurodevelopmental skills in an SCN8A cohort.

OBJECTIVE

To characterize a cohort of patients with SCN8A-related epilepsy and to perform analyses to identify correlations involving the acquisition of neurodevelopmental skills.

METHODS

We analyzed patient data (n = 91) submitted to an online registry tailored to characteristics of children with SCN8A variants. Participants provided information on the history of their child's seizures, medications, comorbidities, and developmental skills based on the Denver II items. Spearman rank tests were utilized to test for correlations among a variety of aspects of seizures, medications, and neurodevelopmental progression.

RESULTS

The 91 participants carried 71 missense variants (41 newly reported) and three truncating variants. Ages at seizure onset ranged from birth to >12 months of age (mean ± SD = 5 months 21 days ± 7 months 14 days). Multiple seizure types with multimodal onset times and developmental delay were observed as general features of this cohort. We found a positive correlation between a developmental score based upon percentage of acquired skills and the age at seizure onset, current seizure freedom, and initial febrile seizures. Analyses of cohort subgroups revealed clear distinctions between patients who had a single reported variant in SCN8A and those with an additional variant reported in a gene other than SCN8A, as well as between patients with different patterns of regression before and at seizure onset.

SIGNIFICANCE

This is the first study of an SCN8A patient cohort of this size and for which correlations between age at seizure onset and neurodevelopment were investigated. Our correlation studies suggest that variants of uncertain significance should be considered in assessing children with SCN8A-related disorders. This study substantially improves the characterization of this patient population and our understanding of the neurodevelopmental effects associated with seizures for SCN8A patients, and provides a clinical context at initial presentation that may be prognostic for developmental outcome.