Dravet syndrome is a rare type of epilepsy, most often due to non-inherited mutations in the SCN1A gene. Symptoms usually appear in the first year of life and are marked by prolonged, uncontrollable seizures. Developmental delays and disabilities often follow as seizures continue.
An accurate diagnosis of Dravet syndrome can be slow to arrive, because the symptoms progress with time and the initial diagnosis depends mainly on the patient’s medical history.
A child’s detailed medical history is essential for a physician to diagnose Dravet syndrome based on tell-tale signs and symptoms. This history includes information about when the seizures started, their frequency and duration, possible or suspected seizure triggers, and observations of the patient’s ongoing development.
Among common characteristics of seizures associated with Dravet syndrome are prolonged seizures (status epilepticus; those lasting for longer than five to 10 minutes), seizures that cannot be controlled with common anti-epilepsy medications, seizures that usually occur on one side of the body (subsequent seizures may switch to the other side), and that can be triggered by a warm bath, a mild illness, exertion, or a fever.
Vaccines are not reported to trigger Dravet syndrome, or to affect its course or outcomes. However, seizures are known to start in children with SCN1A gene mutations shortly after first vaccines are given (between 2 and 6 months old). This may be due to a vaccine causing a fever, and researchers advise parents to give age-appropriate vaccinations to these children.
Most experts favor genetic testing for a child with two or more prolonged seizures in one or both sides of the brain, with or without fever, before 12 months of age, although these tests are not sufficient to diagnose Dravet.
Genetic testing can be done with a simple blood test to detect mutations in the SCN1A gene, which are responsible for about 80 percent of all Dravet syndrome cases. These tests may also be used to investigate the presence of other epilepsy-related genes.
Some SCN1A mutations cause other forms of epilepsy than Dravet syndrome. For this reason, genetic testing alone is not considered conclusive for a diagnosis, and needs to be interpreted in the context of other findings.
The other 10–20% of Dravet patients may have mutations in different genes, most of which are yet to be identified.
An EEG measures the electrical signals that the brain produces, or its activity. In Dravet patients, these signals often look normal initially, but can start showing abnormalities when the patient is between 2 and 3 years old. Abnormal signals can be single events or bursts of waves and spikes.
Magnetic resonance imaging (MRI) may be used to complement other exams.
As with EEGs, MRIs are usually normal at first. However, over time MRI scans may show signs of brain atrophy, abnormal growth of the cortex (the outer layer of the brain), and nerve damage in a brain region called the hippocampus (hippocampal sclerosis) in some individuals.
Other imaging methods, such as single photon emission computed tomography (SPECT) and positron emission tomography (PET) are under investigation as diagnostic tools for Dravet syndrome.
Last updated: June 2, 2021
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