Dravet syndrome (DS) is a refractory epileptic encephalopathy occurring in otherwise healthy infants. Incidence has been estimated at between 1 in 20 000 and 1 in 40 000. DS is more frequent in males than females (ratio of 2:1). Onset occurs during the 1st year of life with clonic/tonic-clonic, generalised and unilateral seizures. The seizures occur every 1-2 months and are often initially associated with fever. Hemiclonic or generalised status epilepticus is common. Other seizure types (usually myoclonus, atypical absences and complex partial seizures) begin during the 2nd or 3rd year of life and although the duration of these seizures decreases during this period, their frequency increases. Trigger factors include eye closing or intermittent photic stimulation (IPS). The disease course is marked by slowing of psychomotor development and onset of behavioural disorders and ataxia. Photosensitivity has also been noted. At least 25% of DS patients have a family history of epilepsy or febrile seizures. DS has been associated with mutations in the SCN1A gene (2q24.3) encoding a voltage-gated sodium channel. These mutations have been implicated in at least two thirds of DS cases and usually occur de novo. Diagnosis of DS is based on the clinical picture: identification of SCN1A mutations does not confirm the diagnosis. During the early stage of the disease, the EEG is normal but anomalies (generalised spike and polyspike waves) appear from the age of 2-3 years. The association of early seizures with febrile episodes may also help orientate the diagnosis. A variant of DS has also been reported (borderline SMEI; SMEB) showing all the clinical manifestations seen in DS but lacking the myoclonic seizures. Differential diagnosis should include early febrile convulsions, Lennox Gastaut syndrome and epilepsy with myoclonic-astatic crisis (see these terms). The seizures do not respond well to antiepileptic drugs but valproate and benzodiazepines (clobazam) appear to be the most effective. More recently, add-on therapy with stiripentol (STP) has been shown to be of benefit: in January 2007, STP obtained orphan drug EU marketing authorisation as an adjuvant treatment for DS. Open clinical trials suggest that topiramate might also be of benefit in children showing a poor response to stiripentol. The use of carbamazepine and vigabatrin should be avoided due to the risk of worsening the seizures. Management may also include a ketogenic diet, and physical and communication therapy. Although the frequency of seizures decreases as the child gets older, the long-term prognosis is poor with cognitive impairment and persistent behavioural problems. Dravet syndrome is also associated with an increased risk of sudden death in childhood, particularly between 2 and 4 years of age.
Last update: May 2007