Adult-Onset Neurological Deterioration in Dravet Syndrome Associated With a Novel SCN1A Missense Variant (p.Gly1371Asp): A Case Report

We report the case of a 26-year-old woman with genetically confirmed Dravet syndrome (DS) who experienced atypical neurological deterioration in early adulthood, despite a previously stable clinical course. Her early history met the classical DS criteria, with the onset of febrile and afebrile seizures in infancy, followed by myoclonic, focal, and absence seizures, as well as developmental delay. Beginning at age 20, however, she developed new symptoms, including progressive tremor, postural instability, frequent gelastic-like seizures, and dysphagia severe enough to require temporary nasogastric feeding. Neuroimaging revealed basal ganglia and thalamic calcifications that had not been present in childhood. Mitochondrial evaluation demonstrated a mild reduction in oxygen consumption, despite normal enzyme activity. Genetic analysis, performed for the first time in adulthood, identified a previously unreported de novo missense variant in <i>SCN1A</i> (c.4112G>A, p.Gly1371Asp). This case highlights the potential for adult-onset phenotypic progression in <i>SCN1A</i>-related epilepsy and may broaden the clinical spectrum of DS, underscoring the importance of ongoing surveillance during adulthood, particularly in patients with rare or novel <i>SCN1A</i> missense variant (p.Gly1371Asp).