NeurometPlus

Incidence

Incidence has been estimated between 1 in 20 000 and 1 in 40 000. It occurs more frequently in males than females with a ratio of 2:1. The prevalence is approximately 6% of epilepsies starting before the age of 3 years. DS has been associated with mutations in the SCN1A gene (2q24.3) which encodes a voltage-gated sodium channel. These mutations have been implicated in at least two thirds of DS cases and usually occur de novo.

Clinical Characteristics

Dravet syndrome is a rare progressive epileptic encephalopathy. Onset is during the first year of life. It peaks at the age of 5 months. It is considered an epileptic syndrome. The characteristics include a family history of epilepsy or febrile convulsions, normal development before onset, seizures often occurring with fever beginning during the first year of life in the form of generalized or unilateral febrile clonic seizures, secondary appearance of myoclonic jerks and often partial seizures. Status epilepticus is common. All patients show variable but usually severe impairment of cognitive function. Psychomotor development is retarded from the second year of life and ataxia, pyramidal signs and inter-ictal myoclonus appear. A SCN1A gene defect is strongly supportive but not diagnostic of Dravet syndrome. The diagnosis of Dravet syndrome is a clinical diagnosis. Brain CT and MRI scans are either normal or show mild cerebral or cerebellar atrophy. The inter-ictal EEG may initially be normal. Within 1 year the EEG may become severely abnormal with slowing and paroxysms of polyspikes or spikes-slow waves become frequent. Focal and mainly multi-focal abnormalities of sharp or spike-slow waves are frequent. In 15% of cases, patients may die either during a seizure or from concomitant diseases. This type of epilepsy is very resistant to all forms of treatment.

Precipitants

Trigger factors include eye closing or intermittent photic stimulation (IPS), febrile illnesses, a raised body temperature and a warm environment (hot baths) and hand waving.

Provocation Tests

None.

Diagnostic Procedures

The diagnosis of Dravet syndrome is a clinical diagnosis. Recently a specific genetic abnormality, called a \"mutation\" has been found in at least 70 per cent of children with SMEI. This mutation is known as the SCN1A mutation. It is likely that other mutations will also be found in children with SMEI. The mutation can be looked for in a simple blood test and this has been very helpful in making or confirming a diagnosis of this epilepsy syndrome. A SCN1A gene defect is strongly supportive but not diagnostic of Dravet syndrome.