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Dravet Syndrome

By Dr Sameer Zuberi, Yorkhill Children’s Hospital, Glasgow

Dravet Syndrome is a severe form of epilepsy which begins in infancy and affects almost every aspect of a child’s life. In 1978 a French Paediatric Neurologist, Charlotte Dravet, described a group of children with a particular pattern of seizures that were not controlled by medication. The most important aspect of this epilepsy syndrome is that infants have completely normal development before the seizures begin but as the condition develops, over months and years, their development may slow and they might even lose skills that they have acquired.

In the 1980s there was a move away from calling conditions after the individual who described them and the term Severe Myoclonic Epilepsy of Infancy (SMEI) was used to describe these children. However, in the 21st Century as knowledge about the syndrome has grown, we know that some children may not have all the features of classical SMEI. To allow us to bring all of the variable presentations together in one group, the preferred term is once again Dravet Syndrome.

The specific features of Dravet Syndrome differ in every child, however, almost all have their first seizure in the first year of life. Usually this is in a febrile illness. Brief febrile seizures are common in childhood, affecting about 4% of children. The first seizures in Dravet Syndrome are often prolonged febrile seizures and characterised by jerking of all four limbs (generalised clonic) or one side (hemi-clonic) of the body. The second and subsequent seizures may also be prolonged and can affect the other side of the body. Sometimes an infant’s first febrile illness is after their first set of immunisations, and if a seizure occurs at this time families and some physicians may understandably, but mistakenly, blame the immunisation for the epilepsy and subsequent developmental problems.

Because febrile convulsions are common, Dravet Syndrome is usually not diagnosed until other seizure types develop. This may delay diagnosis for many months and often years after the onset of seizures. In the second year of life, children may develop sudden shock like jerks (myoclonic seizures) of their limbs or body which may cause them to fall. Generalised seizures may occur without a fever, the child may have staring episodes (atypical absences) and events where their consciousness is partially affected and they make abnormal movements of part of their body (complex partial seizures). A child can have many seizures a day. As these different seizure types emerge, families realise that that their child’s development is not progressing normally. The degree of learning disability in children with Dravet Syndrome is variable but does seem to be linked to the severity of the epilepsy. Other problems such as unsteadiness when walking (ataxia) and behaviour problems may also develop. Children with Dravet Syndrome will usually have had lots of tests. EEG studies may be normal in the early months of the condition but will show a variety of abnormalities with time. MRI scans of the brain are normal and standard blood tests will also be normal.

The mainstay of treatment is anti-epileptic medication. However, many children fail to respond to standard medications and some drugs can even make certain types of seizures worse. After the first four years of life, the frequency of seizures may decline but individuals remain at risk of seizures for the rest of their lives.

There have been two major exciting advances in the knowledge relating to Dravet Syndrome over the last few years. These relate to treatment and understanding the underlying cause. There is increasing evidence that certain medications and combinations of medications are better at controlling seizures in this syndrome. A drug called stiripentol, which is rarely used for other epilepsy types, has a European Orphan Drug License for Dravet Syndrome. When the seizures are controlled, the child is better able to learn and make developmental progress. Therefore the aim should be to make a diagnosis as early as possible.

The second major advance was the discovery that the vast majority of individuals with Dravet Syndrome have a mutation (change) in a gene called SCN1A. This gene holds the DNA code to make a protein which helps control electrical activity in brain cells. The protein is called a sodium ion channel alpha subunit. Although this is a genetic mutation, it is only rarely inherited from a parent. Most frequently, it is a new mutation that occurs shortly after conception. The importance in this discovery lies in the fact that children with Dravet Syndrome can have a genetic diagnosis before the full syndrome has evolved. This saves the child many unnecessary investigations and means that the most appropriate medical treatments can begin earlier than in the past. Therefore advances in treatment and in genetics give families hope for earlier and better seizure control with the possibility of reducing or preventing the learning problems and neurological disability.