DRAVET SYNDROME: AN ATYPICAL CASE REVEALED BY WHOLE EXOME SEQUENCING

Background: Dravet syndrome (DS) is a developmental and epileptic encephalopathy (DEE), caused in most cases by pathogenic variants in SCN1A, with seizure onset between 1 and 20 months of age. Case presentation: We report a girl born to consanguineous parents, with a paternal family history of generalized epilepsy. Her development was normal until a first febrile, refractory status epilepticus at 3 years and 6 months. Over the following year she developed typical absence and generalized tonic-clonic seizures of increasing frequency and duration. An EEG recorded bilateral frontocentral spike-and-wave discharges predominating on the right; brain MRI was normal. Whole exome sequencing identified a heterozygous missense variant in SCN1A, NM_001165963.4:c.2839G>A (p.Val947Met), classified as pathogenic (class 5) by the diagnostic laboratory according to ACMG/AMP criteria. Seizures persisted on valproate monotherapy, then stopped after the stepwise introduction of clobazam, stiripentol and levetiracetam. She has remained seizure-free since the age of 4 years, with stable development and no cognitive, motor or behavioural deterioration after more than 12 months of follow-up (last visit at the age of 4 years and 5 months).