From genotype to phenotype in Dravet disease

Abstract

Dravet syndrome combines clonic generalized, focal or unilateral seizures, beginning within the first year of life, often triggered by hyperthermia whatever its cause, including pertussis vaccination. Long-lasting febrile seizures are frequent in infancy and repeat status epilepticus (SE) has negative prognostic value. Massive myoclonus, rare absences, complex partial seizures and generalized spikes may appear several years later. Myoclonic status may occur in childhood, but acute encephalopathy with febrile SE followed by ischemic lesions and psychomotor impairment, the most severe condition, occurs mainly within the first five years of life. Generalized tonic-clonic and tonic seizures in sleep predominate in adulthood. Non epileptic manifestations appear with age, including intellectual disability, ataxia and crouching gait. Incidence of SUDEP is high, whatever the age. SCN1A haploinsufficiency producing Na_V1.1 dysfunction mainly affects GABAergic neurons. In cortical interneurons it explains epilepsy, in cerebellum the ataxia, in basal ganglia and motor neurons the crouching gait, in hypothalamus the thermodysregulation and sleep troubles, and dysfunction in all these structures contributes to psychomotor delay. Valproate, stiripentol, topiramate and bromide are the basis of antiepileptic treatment, whereas inhibitors of sodium channel worsen the condition. Benzodiazepines seem to facilitate acute encephalopathy when given chronically, and they should be restricted to SE. Ketogenic diet is useful in both chronic and acute conditions. Only targeting SCN1A haploinsufficiency and Na_V1.1 dysfunction could improve non epileptic manifestations of this condition that deserves being considered as a disease, not only as an epilepsy syndrome.

Keywords: Dravet syndrome; GABAergic neurons; Na(V)1.1; SCN1A; Status epilepticus.