Impact of variant subtype on electro-clinical phenotype of Dravet syndrome- a South Indian cohort study.

• Largest series from south India on Dravet syndrome genotype phenotype correlations. • Truncating and missense variants appeared to be equally prevalent. • Developmental outcomes did not differ between phenotypes. • Truncating variants increased the risk of multiple seizure types and ASM resistance. • 28.6% patients with missense variants were seizure free versus none with truncating. We aimed to compare the electroclinical correlates of truncating and missense variants of SCN1A variants in children with Dravet syndrome (DS) and to determine phenotypic features in relation to variants identified and seizure outcomes. A single center prospective study was carried out on a South Indian cohort. Patients below 18 years of age who met the clinical criteria for DS who had undergone genetic testing and completed a minimum of one year follow up were included. We compared the differences in clinical profile, seizure outcome, developmental characteristics and anti-seizure medication (ASM) responsiveness profiles between patients with missense and truncating variants. Out of a total of 3967 children with drug-resistant epilepsy during the period 2015–2021, 49 patients who fulfilled the inclusion criteria were studied. Thirty-seven had positive genetic tests, out of which 29 were SCN1A variants and 9 were other novel variants. The proportion of missense (14; 48.3%) and truncating SCN1A variants (15; 51.7%) was similar. A significant trend for developing multiple seizure types was noted among children with truncating variants (p = 0.035) and seizure freedom was more likely among children with missense variants (p = 0.042). All patients with truncating variants had ASM resistant epilepsy (p = 0.020). Developmental outcomes did not differ between the variant subtypes. Our results show that children harbouring missense variants demonstrated a significantly lower propensity for multiple seizure subtypes and a higher proportion with seizure freedom. However developmental implications appear to be independent of variant subtype. [ABSTRACT FROM AUTHOR]