Dravet Syndrome, also known as Severe Myoclonic Epilepsy of Infancy (SMEI), is a progressive childhood neurodevelopmental disorder characterized by severe epilepsy that does not respond well to treatment.  Estimates of the prevalence of this rare disorder have ranged from 1:20,000 to 1:40,000 births, though incidence may be far greater as new genetic evidence is discovered.  It occurs more frequently in boys than in girls, but knows no geographic or ethnic boundaries.

The course of Dravet Syndrome is highly variable from child to child.  It begins in the first year of life.  Development is normal prior to the onset of seizures.  In most cases the first seizures are correlated with fever and are generalized or unilateral tonic-clonic seizures.  These seizures are often prolonged and may lead to status epilepticus.  In time seizures increase in frequency and become more likely to occur without fever.  Additional seizure types appear, most often myoclonic, atypical absence, and complex partial seizures.  More About Seizures

During the second year of life, progressive regression of aquired skills and developmental delays are usually observed to varying degrees and additional neurological symptoms, such as ataxia may appear.
More About Development

Additional features that are seen in most children with Dravet Syndrome are poor regulation of body temperature and increased susceptibility to infection.  For a significant number of these children secondary problems can also include sleep disturbance, slowed physical growth, movement disorders, and orthopedic disorders.  More About Secondary Features

Identifying the causes of Dravet Syndrome presents complex research problems and investigations are ongoing.  One known cause is mutations of the SCN1A gene on chromosome 2.  The SCN1A gene contains instructions for the synthesis of proteins that regulate the function of sodium ion channels in neuron cells.  The function of these sodium channels is to properly balance the amount of sodium ions inside and outside the cell, which is important for the maintenance of the healthy rhythm of electrical activity in the brain.  When they do not function properly, imbalances occur, causing hyper-excitability of the neuron cells and lowering the seizure threshold.  More About Sodium Channels

Researchers have documented many different mutations of the SCN1A gene that result in febrile, sodium channel epilepsies, however most of them do not result in the severe form known as Dravet Syndrome or SMEI.  There is a broad spectrum of severity, including benign Generalized Epilepsy with Febrile Seizures (GEFS), GEFS+, Severe Myoclonic Epilepsy, Borderline (SMEB) and Dravet Syndrome/SMEI.

                                                                                                                               Dravet Syndrome
ß GEFS -------------------- GEFS+ ----------------------- SMEB -------------------------SMEIà


Mutations of the SCN1A gene have an autosomal dominant inheritance pattern, meaning that they are passed from parent to child.  However, in Dravet Syndrome, although at least a fourth of the affected individuals have some history of febrile seizures or epilepsy in their extended family, the mutations nearly always occur “de novo”, meaning that neither parent tests positive for the gene mutation and it is thought to have occurred spontaneously after conception.  Much remains to be understood about the causes of Dravet Syndrome and research is ongoing.  More About Genetics

At this time, the treatments available for Dravet Syndrome are to improve symptoms, primarily anticonvulsant medications to control seizures.  The seizures are very resistant to therapy and the response to different medicines can be highly variable from child to child.  Certain medicines have been found to be the most useful for most individuals with Dravet Syndrome, a few others have been quite consistently found to have an aggravating effect.  The helpfulness of other anticonvulsant therapies, such as the Ketogenic Diet and the VNS, are in ongoing evaluation.  Once again, results tent to be highly variable from child to child.  Other treatments such as orthotics, physical therapy, occupational therapy, and communication therapy may improve comfort and function.  More About Treatment

Outcomes, once again, tend to be variable.  For most individuals the progression of Dravet Syndrome begins to stabilize after the age of four.  Partial and myoclonic seizures may attenuate, and in some cases disappear.  Convulsive seizures, though their frequency and intensity may moderate, usually persist.  Fever continues to provoke seizures and can still lead to status epilepticus.  Communication, motor, and cognitive function stabilize, but significant delays remain to varying degrees.  Despite being at increased risk for accidents, infection, status epilepticus, and sudden unexpected death, an individual with Dravet Syndrome has an 85% chance of surviving into adulthood.  Because this disorder is rare and has relatively recently been identified as a distinct syndrome, little is known about long-term prognosis and life expectancy.

More About Dravet Syndrome