Dravet syndrome

Dravet syndrome is a rare form of childhood epilepsy but possibly more common than was previously thought. Out of 500 children with epilepsy, 2 or possibly 3 children are likely to have this form of epilepsy. It is also known as an ‘epileptic and developmental encephalopathy’ because the epileptic seizures and the abnormal EEG are thought to be important in these children’s developmental delay and learning difficulties.

The epilepsy usually starts with seizures that may seem to be very similar to febrile convulsions. The more typical features of Dravet syndrome usually become more obvious during the second year of life.

Other names for Dravet syndrome

Severe myoclonic epilepsy in infancy (SMEI), though this name is only rarely used now.

Symptoms

The seizures begin in the first year of life, usually at around 6 to 10 months of age. They are most often associated with a high temperature (febrile seizure or febrile convulsion). They often involve just one side of the body, although both sides of the body may also be involved. The seizures are characterised by stiffness and jerking (called a tonic-clonic seizure), or just repeated jerking (called a clonic seizure). These ‘febrile convulsions’ in Dravet syndrome are usually long, and certainly longer than the more common febrile seizures or convulsions. The seizures in Dravet syndrome last for 15 or 30 minutes and often much longer. This is called febrile convulsive status epilepticus and is common in the first year of life. However, at this time it can be difficult to differentiate or separate these children from others with briefer febrile convulsions, who do not go on and develop other types of seizure.

During the second year of life the seizures become more frequent and persistent, and are often more obviously focal (previously called partial) involving one part of the body. They may happen with or without a fever, and at any time of day and night. In addition to the tonic-clonic seizures, myoclonic seizures (‘myo’ meaning muscle, and ‘clonus’ meaning jerk) and focal seizures become common. Often the children are photosensitive (have seizures brought on by flashing or flickering lights or even certain patterns such as checked or striped materials). A few children are very sensitive to these patterns. Seizures may also sometimes be brought on by hot environments or hot showers or baths.

The early development of children with Dravet syndrome is usually normal. However, the child’s development starts to slow down and children may lose skills towards the middle or certainly by the end of the second year of life. The child’s speech and language is particularly affected. Their manner of walking (called ‘gait’) is also abnormal and is quite fast and unsteady (called ‘ataxia’).

Diagnosis

A full history and description of the seizures that have happened in the past and at the time the child attends their hospital appointment is very important. It is also important for parents to give the doctor a detailed account of their child’s development. Videos of the child’s seizures may also be helpful.

The EEG, which records the electrical activity in the brain, is usually normal early on in this condition. By the time the child is 18 months old, the EEG shows abnormal activity, with spike and wave or polyspike discharges. These happen either as a single event, or in bursts. They may be generalised involving the whole brain, or happening just from one small area of the brain. Some, but not all, children with Dravet syndrome show EEG evidence of sensitivity to flashing or flickering lights, called photosensitivity. The photosensitivity is more common in younger children with Dravet syndrome aged between 1 and 5 years of age. It becomes much less common after 5 years of age. Brain scans in children with Dravet syndrome are usually normal.

A specific genetic abnormality, called a ‘mutation’ has been found in at least 8 out of 10 children with Dravet syndrome. This mutation usually involves the SCN1A gene and is therefore known as the ‘SCN1A’ mutation. A very large number of different mutations on this gene have been found in people with Dravet syndrome. However, rarely mutations may also be found on other genes, including on the SCN1B gene. It is very likely that some patients with Dravet syndrome will be found to have mutations in different genes. One of the difficulties is that children may present with what appears to be possible Dravet syndrome and genetic analysis shows they have a mutation in a different gene. Doctors then have to ask the question as to whether the child does have Dravet syndrome with a completely new mutation – or whether the child has a different epilepsy syndrome with its ‘own’ mutation. This question will only be answered with more research. The research must be clinical – to obtain a better understanding of the clinical features of the epilepsy syndrome – and also genetic. This will then allow doctors to make a clearer link between the different epilepsy syndromes and the gene mutations that have been found.

A mutation can be looked for in a simple blood test. The discovery of this mutation has been very helpful in making or confirming a diagnosis of this epilepsy syndrome. About 90% of mutations are new or ‘de novo’ mutations. This means that the mutation has not been inherited from a parent, but it is a new mutation that has started for the first time in the child. Because of this, it is very un-common for the same parents to have another child with Dravet syndrome. If this does happen, the parents will need to have very detailed genetic testing. However, in identical twins, if one twin develops Dravet syndrome, then it is very likely that this other twin will also have the condition.

In some families a mutation in the SCN1A or SCNIB gene may cause a different form of epilepsy such as GEF+.

Treatment

Dravet syndrome is one of the epilepsy syndromes that is most resistant to epilepsy medicines. Sodium valproate (Epilim) or topiramate (Topamax) are usually tried first. Other medicines which are helpful include clobazam (Frisium) and stiripentol (Diacomit).

Some medicines should be avoided as they may cause an increase in seizures in children with Dravet syndrome. These medicines are carbamazepine, gabapentin, lamotrigine, oxcarbazepine, phenytoin, pregabalin, tiagabine and vigabatrin. Sodium valproate should not be offered as a first treatment to women and girls of childbearing potential unless other options don’t work or are not tolerated. This includes young girls who are likely to need treatment into their childbearing years. If it is prescribed to a girl or woman of childbearing potential, a pregnancy prevention programme should be in place. This is because sodium valproate taken during pregnancy can harm the baby.

Many children with Dravet syndrome seem to respond best to a specific combination of 3 epilepsy medicines. In fact, Dravet syndrome is the only epilepsy syndrome when 3 epilepsy medicines used together are better than 1 or 2.  This combination is sodium valproate, stiripentol and clobazam. It is very important that only specialist epilepsy doctors, called paediatric neurologists, prescribe this combination of medicines. Other treatments that might be helpful include clonazepam (Rivotril), topiramate (Topamax), zonisamide (Zonegran) and levetiracetam (Keppra). A course of a steroid (called prednisolone) may also be helpful for a few weeks if a child’s epilepsy is going through a difficult time. The ketogenic diet may also be helpful but it may take a number of weeks to be effective. The diet will usually have to be given with at least one epilepsy medicine.

Another medicine, called cannabidiol (Epidiolex) has recently been shown to be effective in the treatment of Dravet syndrome. The medicine reduces the number of the different seizures the child has and may help improve their development and also their behaviour.

Information about epilepsy medicines for children can be found on the Medicines for Children website.

A child is very likely to have prolonged or repeated seizures as part of Dravet syndrome. The hospital doctor (paediatrician or paediatric neurologist) will discuss a ‘rescue’ or emergency care plan to treat any prolonged or repeated seizures that may happen at home. This rescue or emergency care plan is important for the child.

Because children with Dravet syndrome always have some degree of learning disability, they will also need a full educational assessment and support.

There has been – and continues to be – a lot of research into Dravet syndrome. This research includes different medicines and treatments. Some new information suggests a medicine, called fenfluramine, might also be effective but much more research needs to be done. You could ask your child’s hospital doctor about this and they will be able to discuss this with you.

Outlook

The seizures continue to be very difficult to control, throughout childhood. Learning difficulties are very common and can range from mild to very severe. These difficulties usually persist and only rarely improve. Many children will also show some signs of autism and this may become obvious at 3 or 4 years of age. As the condition progresses most children become more unsteady (ataxic) on their feet. They also walk with a rather fast and slightly crouched pattern. Children with Dravet syndrome will need to be cared for throughout their lives. Usually by the age of 14 or 16 years, the seizures tend to become less frequent but they still happen.

Finally, and this is often difficult to talk about, children with Dravet syndrome under the age of 5 or 6 years seem to be at a slightly higher risk of SUDEP (sudden unexpected death in epilepsy). It would be helpful for you to discuss this with your child’s hospital doctor.

Support

Contact
Charity for families of disabled children.
Freephone helpline: 0808 808 3555
Website: contact.org.uk
Email: info@contact.org.uk

Dravet Syndrome UK
PO Box 756
Chesterfield
S43 9EB
Phone: 07874 866937
Website: dravet.org.uk
Email: info@dravet.org.uk

What is a syndrome?

A syndrome is a group of signs and symptoms that, added together, suggest a particular medical condition. In epilepsy, examples of these signs and symptoms would be things like the age at which seizures begin, the type of seizures, whether the child is male or female and whether they have physical or learning disabilities, or both. The results of an electroencephalogram (EEG) are also used to help identify epilepsy syndromes.
If you would like to know more about an epilepsy syndrome, please speak to your doctor. If you would like to know more about epilepsy in general, please contact Epilepsy Action.