WHAT IS DRAVET SYNDROME?
Dravet syndrome is a rare and severely disabling type of epilepsy presenting in infancy, sometimes called a catastrophic epilepsy. It was first described in 1978 by Charlotte Dravet, a paediatric epilepsy specialist working in Marseille. Other names that have been used for the condition include Severe Myoclonic Epilepsy of Infancy and Severe Polymorphous Epilepsy of Infancy.
A ‘syndrome’ is a group of signs and symptoms that, when considered together, suggest a particular medical condition. An epilepsy syndrome is diagnosed from the combination of age of onset of seizures, the different types of seizures, how they change over time, findings on EEG tests and other features such as behaviour and learning. As such, epilepsy is just one part of Dravet syndrome; there are various other health conditions and symptoms, which are often found in children with the condition.
Dravet syndrome is rare with latest research showing it affects approximately 1 in 19,000 people. Normally, the first seizure takes place in the first year of life; three-quarters of these seizures accompany a high fever caused by an illness. Sometimes, if a child has a fever caused by immunisation, this might be associated with a seizure. At first, doctors may diagnose a one-off febrile convulsion (a ‘fit’ that a child might have associated with a very high fever). Febrile convulsions are fairly common and, while very alarming for parents, most children tend to have normal development and have only one or very few seizures restricted to early childhood. However, with Dravet syndrome, other seizures follow, increasing in severity.
Seizures in the first year of Dravet syndrome are often clonic (jerking movements), prolonged, and tend to affect one side of the body.
The child’s development during the first year of life is usually normal; after this first year, a range of seizures may appear including:
- Myoclonic seizures, single or multiple muscle jerks, which may involve one part of the body or the whole body
- Atypical absences (where the child will stare) with brief loss of awareness
- Focal seizures, which may involve loss of awareness
- Non-convulsive status where the child develops a groggy, poorly functional state
- Serial seizures or status epilepticus, a prolonged seizure or a cluster of shorter seizures with little or no recovery in between.
Patients with Dravet syndrome are particularly prone to status epilepticus, therefore swift medical intervention is essential to stop the seizure as soon as possible to reduce the risk of damage to the brain or breathing problems caused by a long seizure.
From the second year onwards, the child’s development slows down or regresses, sometimes severely. Features of autism and attention deficit hyperactivity disorder (ADHD) are common.
Dravet patients often experience mobility issues, in particular with regards to an unsteady gait called ataxia. Some patients are affected severely, whilst in others the problem may be less severe.
WHY DOES MY CHILD HAVE DRAVET SYNDROME?
About 80% of patients with Dravet syndrome have a mutation (or change) in a gene called SCN1a. The SCN1a gene contains instructions (the genetic code) for the creation of a protein that controls how sodium ions move into the cells in our bodies. A change in this gene may lead to faulty functioning of this protein, called a sodium ion channel, in the brain. The movement of sodium ions in and out of cells help control electrical messages in the brain so a faulty ion channel can cause seizures. Not all mutations to this gene cause Dravet syndrome. Other SCN1a mutations are associated with other less severe forms of epilepsy, such as Genetic Epilepsy with Febrile Seizures + (GEFS+).
In Dravet syndrome, the gene mutation nearly always arises spontaneously and is not passed down (inherited) from parents. It is rare for mutations of the SCN1a gene to be passed from parent to child; however, some people with Dravet syndrome may have some history of febrile seizures or epilepsy in their extended family. Much remains to be understood about the causes of Dravet syndrome and research is ongoing. In children with Dravet syndrome who do not have SCN1a mutations, other genetic mutations are being explored.
Above all, the one thing that families need to understand is that it is not their fault. Gene mutations happen in everyone. It is simply random when they occur in an important gene like SCN1a.
WHAT IS THE CAUSE OF DRAVET SYNDROME
The course of Dravet syndrome is variable from one child to another. Seizures typically begin during the first year of life and neuro-development is normal prior to their onset. In most cases, the first seizures occur with fever and are generalised tonic-clonic (involving the whole body) or one-sided convulsions.
These seizures are often prolonged (lasting longer than five minutes) and may require emergency intervention. Over the next weeks or months, seizures increase in frequency and begin to occur without fever. Additional seizure types later appear. Most commonly, these are myoclonic (single jerks), focal or atypical absence seizures (usually involving staring and unresponsiveness).
During the second to fourth year of life, varying degrees of developmental delay typically become apparent. Other symptoms – such as ataxia (unsteadiness), sleep disturbance, and behaviour problems – may also develop. As children grow older, focal and myoclonic seizures may lessen, and in some cases disappear, but convulsive seizures typically persist, often occurring from sleep.
Prolonged seizures continue to be a risk and may still be more likely to occur with fever or illness. Communication, motor and cognitive functions stabilise, but significant delays persist.
Previously children with an apparently milder clinical course, usually without myoclonic seizures, have been described as having severe myoclonic epilepsy borderline (SMEB), it is now accepted to classify these children as also having Dravet syndrome.
Children with Dravet syndrome are at a higher risk of sudden unexplained death in epilepsy (SUDEP) than children with other types of epilepsy.
Children with Dravet syndrome are at a higher risk of sudden unexplained death in epilepsy (SUDEP) than children with other types of epilepsy. Despite this they have an 85% chance of surviving into adulthood. Adults are increasingly being recognised with this type of epilepsy as adult specialists become more aware of the condition.
IS THERE A CURE FOR DRAVET SYNDROME?
Unfortunately, there is no cure for Dravet syndrome. Treatment focuses on controlling or minimising seizures in order to minimise their impact on development and reduce injuries due to seizures. Anti-epileptic drugs are used, but these are not always effective in people with Dravet syndrome. Comprehensive testing and support is required for the multiple challenges that people with Dravet syndrome and their families face. Many children with Dravet syndrome have a good life expectancy, however children who develop severe disability may have problems which will affect their lifespan.
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