Risk factors for Dravet syndrome were determined in 96 children who experienced febrile seizures before age one year, in a retrospective study at Okayama University and other centers in Japan. Clinical characteristics were compared in 46 patients who had developed Dravet syndrome and 50 without the syndrome. Significant risk factors included an age of onset of febrile seizure <7 months, a total of >5 seizures, and prolonged seizures >10 min. Other highly predictive factors were hemiconvulsions, partial seizures, myoclonic seizures, and hot water-induced seizures. A total clinical score of 6 or above was the cut-off value for a high risk of Dravet syndrome. (Each risk factor was assigned a score of 0-3, based on the p-value; >5 seizures [3], hemiconvulsion [3], prolonged seizure [3], onset <7 mos [2], hot water-induced seizure [2], focal or myoclonic seizure [1]). SCN1A mutations were detected significantly more often in the Dravet group (41-43%) than in the non-Dravet syndrome group (0-12%) of patients. [1]

COMMENT. In this practical screening test for the differentiation of Dravet syndrome from febrile seizures, if the patient has a clinical risk score of 6 or more, there is a high risk of Dravet syndrome. SCN1A mutation analysis is recommended if available in infants with a risk score of -/ > 6. Dravet syndrome or SMEI (severe myoclonic epilepsy of infancy), an intractable form of epilepsy, is difficult to differentiate from a febrile seizure disorder before the first birthday. Seizures are febrile hemiclonic or generalized tonic-clonic, frequently recurrent and prolonged, and are complicated by status epilepticus during infancy. Myoclonic, focal, absence and atonic seizures evolve between 1 and 4 years, and are accompanied by slow development and regression. Neurologic abnormalities include spasticity, ataxia and cognitive impairment. SMEI is one of a spectrum of infantile epileptic encephalopathies with SCN1A mutations, (see Ped Neur Briefs April 2007;21:25-26). Early diagnosis should allow more accurate parental counseling and more effective long-term treatment.