Fenfluramine in refractory SCN1A-related 'genetic epilepsy with febrile seizures plus'.
A child with SCN1A-related 'genetic epilepsy with febrile seizures plus' (GEFS+) presented in infancy with recurrent febrile and afebrile seizures, frequently progressing to generalised tonic-clonic status epilepticus. Despite a severe seizure burden and typical Dravet-like triggers, neurodevelopment remained entirely normal and a familial SCN1A variant supported a diagnosis of GEFS+. The variant (c.5666T>A, p.Met1889Lys) was classified as a variant of uncertain significance fulfilling PM2, PP1 and PP3 criteria and absent from The Genome Aggregation Database (gnomAD) and ClinVar. Identification of the same variant in a neurodevelopmentally normal parent supported inherited GEFS+ rather than Dravet syndrome. After treatment failure with sodium valproate, clobazam and topiramate, low-dose fenfluramine (2.2 mg/day, 0.15 mg/kg/day) achieved seizure freedom maintained for more than 1 year with no adverse effects. This dose is substantially lower than the 0.2-0.7 mg/kg/day used in Dravet syndrome trials, suggesting GEFS+ may require lower therapeutic thresholds.