Dravet Syndrome, also known as SMEI (Severe Myoclonic Epilepsy in Infancy) is a severe form of epilepsy that is characterized by frequent, prolonged seizures, developmental delay, speech impairment, hypotonia, ataxia, sleep disturbances, and other health issues.
DS is named after Charlotte Dravet, a French Paediatric Neurologist, who identified the syndrome in 1978.
ICD-10 Code
G40.4
Symptoms
The main symptom of the syndrome is seizures (seizure types caused by DS are typically tonic-clonic and involve muscle jerks or other body movements). Patients with DS can also experience the following related symptoms:
- problems with the autonomic nervous system – it is a control system that acts largely unconsciously and controls heartbeat, breathing, and digestion;
- low motor tone, which can lead to painful foot problems;
- low humoral immunity – this leads to a decreased capacity to create antibodies that fight infection;
- nutritional problems.
Note – typically, the first seizure takes place in the first year of life.
Between the ages of 1 and 5 years, many affected children start to show signs and symptoms of developmental delay, which can include:
- slow growth and poor weight gain;
- poor coordination;
- behavioral issues like irritability, hyperactivity, and characteristics associated with autism;
- slow speech development;
- unsteady gait.
Note – the syndrome usually improves from age five.
Causes
An estimated 80 percent of patients with DS have a mutation in a gene called SCN1a. Approximately 700 mutations in the SCN1A gene, which are associated with the syndrome, have so far been identified. Most mutations are de novo, however, in 5 to 10 percent, these mutations are familial and commonly part of generalized epilepsy with febrile seizures-plus spectrum.
This gene contains instructions for the creation of a protein that controls how sodium ions move into the cells in the human body. These channels play an essential role in a cell’s capacity to transmit and generate electrical signals.
Some cases of DS do not have a clear genetic cause. However, there is a chance that kids who meet most of the following criteria have DS, even if they do not have a mutation in the SCN1A gene:
- seizures that do not respond to epilepsy drugs, with seizures continuing past age 2;
- tonic-clonic seizures or myoclonic, hemi-clonic;
- 2 or more seizures which last more than 10 minutes;
- 2 or more seizures, without or with fever, before age 1;
- normal development before the 1st seizure.
Complications
SCN1A mutation status may be correlated with heart abnormalities, bradycardia (a slower than normal heart rate), and delayed puberty.
Patients with DS are particularly prone to status epilepticus (a single epileptic seizure lasting more than five minutes). Hence, to reduce the risk of breathing problems or damage to the brain caused by a long seizure, rapid medical intervention is important to stop the seizure as fast as possible.
Moreover, kids that suffer from DS can get their teeth slightly late, which results in teeth of smaller size and different shape.
Dravet Syndrome Statistics & Life Expectancy
Out of 500 children with epilepsy, only one is likely to have this form of epilepsy. According to statistics, 1 in 20,000 to 1 in 40,000 people has DS. Also, 3 to 8 percent of the children who have their first seizure by one-year-old may have DS. In the United States, 1 out of 15,700 infants has DS.
Dravet syndrome-related mortality is about 10 to 15 percent, with most deaths occurring in children or young adults. ”An individual with DS has an 85% chance of surviving into adulthood,” according to NIH (National Institutes of Health).
The majority of deaths occur due to status epilepticus (SE) and SUDEP (sudden unexpected death in epilepsy patients). The cause of sudden unexpected death in epilepsy patients remains ambiguous, however, it may be explained by genetic susceptibility to SUDEP and epilepsy severity. Other causes of death include – injury or drowning as a consequence of SE.
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Diagnosis
Early diagnosis is essential to avoid inappropriate treatment and enable the timely provision of rehabilitation, counseling, and psychological support.
If your child has experienced 2 or more prolonged seizures in the first 12 months of life, it is recommended to speak to your neurologist.
Diagnosis can be confirmed by genetic testing, which shows mutations within the SCN1A gene.
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Treatment
There is no cure for DS. The treatment is focused on minimizing or controlling seizures in order to reduce injuries due to seizures and minimize their impact on development.
Benzodiazepines (a class of psychoactive drugs) are used for long-lasting seizures, and valproate (a medicine called a mood stabilizer) is commonly administered to prevent the recurrence of febrile seizures, however, these treatments are typically insufficient.
Because children with DS always have some degree of learning disability, they will require a full educational support and assessment.
Cannabidiol (brand name – Epidolex) was approved in June 2018 by the U.S. FDA for the treatment of seizures associated with DS for children ages 2 and older. According to studies, the median frequency of seizures per 30 days was decreased from 12.4 to 5.9 with Epidolex.
Vagus nerve stimulation – it is a treatment that involves delivering small pulses of energy to the brain from one of the vagus nerves.
Warning
Certain anticonvulsant drugs (gabapentin, lamotrigine, carbamazepine, and phenytoin), which are classed as sodium channel blockers, should not be used by DS patients.
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Prognosis
Even after three decades of research, DS remains a difficult-to-treat epileptic disorder with a significant impact on affected kids and their families. Children with DS will usually need to be cared for throughout their lives.
Moderate to severe cognitive impairment into adulthood is common. Preventing the occurrence of convulsive status epilepticus may substantially improve the long-term prognosis.
Development is usually normal in the 1st year of life, with regression or plateauing in later years. The frequency of broken bones, osteopenia (a decreased bone density but not to the extent of osteoporosis), and gait disturbances increased with age. In rare cases, children stabilize and improve after age 6.
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References https://www.nejm.org/doi/full/10.1056/NEJMoa1611618 https://www.omicsonline.org/current-trends-in-dravet-syndrome https://www.sciencedirect.com/science/article/pii/S0920121106002014