Cognitive development in Dravet syndrome: a retrospective, multicenter study of 26 patients

epilepsy started at the mean age of 5.6 months. All patients experienced prolonged convulsive seizures, whereas absences and myoclonus were reported in 17. Cognitive outcome was poor in almost all patients; the mean dGQ was 33 points, varying from 6-77 points. The analysis of individual cognitive profiles identified seven patients in whom the dGQ was < 20 points; the main clinical characteristic in this subset of patients was lack of early absences and myoclonus. The statistical analysis of the whole series failed to reveal significant differences in cognitive outcome with regard to the presence of SCN1A mutations and their type. In particular, mutation-carrier patients with the best cognitive outcome harbored either missense or truncating mutations.