Severe myoclonic epilepsy of infancy
| Dravet syndrome | |
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| Synonyms | Severe myoclonic epilepsy of infancy, severe polymorphic epilepsy of infancy, borderland SMEI (SMEB), borderline SMEI, intractable childhood epilepsy with generalised tonic clonic seizures (ICEGTCS) |
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| Specialty | Neurology |
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Dravet syndrome, previously known as severe myoclonic epilepsy of infancy (SMEI), is a type of epilepsy with seizures that are often triggered by hot temperatures or fever. It is treated with anticonvulsant medications. It often begins around six months of age.
Dravet syndrome has been characterized by prolonged febrile and non-febrile seizures within the first year of a child’s life. This disease progresses to other seizure types like myoclonic and partial seizures, psychomotor delay, and ataxia. It is characterized by cognitive impairment, behavioral disorders, and motor deficits. Behavioral deficits often include hyperactivity and impulsiveness, and in more rare cases, autistic-like behaviors. Dravet syndrome is also associated with sleep disorders including somnolence and insomnia. The seizures experienced by people with Dravet syndrome become worse as the patient ages, as the disease is not very observable when symptoms first appear. This coupled with the range of severity differing between each individual diagnosed and the resistance of these seizures to drugs has made it challenging to develop treatments.
Dravet syndrome appears during the first year of life, often beginning around six months of age with frequent febrile seizures (fever-related seizures). Children with Dravet syndrome typically experience a lagged development of language and motor skills, hyperactivity and sleep difficulties, chronic infection, growth and balance issues, and difficulty relating to others. The effects of this disorder do not diminish over time, and children diagnosed with Dravet syndrome require fully committed caretakers with tremendous patience and the ability to closely monitor them.
Febrile seizures are divided into two categories known as simple and complex. A febrile seizure would be categorized as complex if it has occurred within 24 hours of another seizure or if it lasts longer than 15 minutes. A febrile seizure lasting less than 15 minutes would be considered simple. Sometimes modest hyperthermic stressors like physical exertion or a hot bath can provoke seizures in affected individuals. However, any seizure uninterrupted after 5 minutes, without a resumption of postictal (more normal; recovery-type; after-seizure) consciousness can lead to potentially fatal status epilepticus.
In most cases the mutations in Dravet syndrome are not hereditary and the mutated gene is found for the first time in a single family member. In 70–90% of patients, Dravet syndrome is caused by nonsense mutations in the SCN1A gene resulting in a premature stop codon and thus a non-functional protein. This gene normally codes for neuronal voltage-gated sodium channel Na(V)1.1. In mouse models, these loss-of-function mutations have been observed to result in a decrease in sodium currents and impaired excitability of GABAergic interneurons of the hippocampus. The researchers found that loss of NA(V)1.1 channels was sufficient to cause the epilepsy and premature death seen in Dravet syndrome.
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