Children With SCN8A Gene Mutation Can Present With The Following:
- Early Infantile Epileptic Encephalopathy-13 (EIEE13), also known as Ohtahara Syndrome
- Benign Familial Infantile Seizures-5 (BFIS5) and paroxysmal dyskinesia (abnormal movements)
- Intellectual disability alone without epilepsy
What Do The Seizures In SCN8A-Related Epilepsy Look Like?
- Seizures in people with the SCN8A variant mutation causing EIEE13 are frequent, can occur multiple times a day, and are resistant to anti-seizure medications.
- Seizure types include generalized tonic-clonic, tonic, myoclonic, atypical absence, and infantile spasms.
- In addition to seizures, children also have muscle spasms, abnormal movements, low or high muscle tone, ataxia (lack of muscle coordination), developmental and cognitive disabilities, and features similar to autism.
- Seizure types in people with the SCN8A variant mutation causing BFIS5 are focal, focal to bilateral tonic-clonic, or generalized tonic-clonic seizures.
- Seizures start during the first year of life and, in general, stop by 2 years of age. However, about a third of people have a single, unprovoked seizure later in life.
- In addition to seizures, 30% of people may also have paroxysmal dyskinesia (abnormal movement) that is characterized by dystonia (muscle contractions), choreoathetosis (irregular muscle contractions with twisting), or ataxia (lack of muscle coordination) that usually present during puberty.
- Cognition, development of motor skills, and EEGs (electroencephalograms) between seizures are normal in the majority of the cases.
How Is SCN8A Inherited?
- People with the SCN8A variant mutation causing EIEE13 appear to be de novo (new mutation) or sporadic (random). Recurrence risk for families with a child affected with EIEE is higher than in general population.
- People with the SCN8A variant mutation causing BFIS5 and paroxysmal dyskinesia inherit this as autosomal dominant, which means a child of a parent with the disease has a 50% chance of inheriting it.
- People with the SCN8A variant mutation causing intellectual disability alone without epilepsy appear to be de novo (new mutation) or sporadic.
How is SCN8A-related epilepsy diagnosed?
- Your doctor will take a history and examine your child.
- Your doctor will order an EEG and in many instances a prolonged video EEG is required.
- Your doctor will also order genetic testing to establish the diagnosis; and an electrocardiogram (EKG) to evaluate the possibility of cardiac arrhythmia. Your doctor may refer you to a geneticist and/or genetics counselor.
- MRI (magnetic resonance imaging) scans are usually normal at the onset of seizures; however, some people have been reported to have abnormal findings that may include cerebral atrophy (wasting away of existing cells) and hypoplasia (underdevelopment) of the corpus callosum.
How Is SCN8A-Related Epilepsy Treated?
Seizures in people with the SCN8A variant mutation causing BFIS5 are usually well controlled with medication.
Seizures in children with SCN8A variant mutation causing EIEE13 are frequent and occur multiple times a day. Seizures tend to be resistant to anti-seizure medication.
- Medications often tried are carbamazepine (Tegretol), oxcarbazepine (Trileptal), phenytoin (Dilantin) which may require high doses, lacosamide (Vimpat), lamotrigine (Lamictal), rufinamide (Banzel), and valproate (Depakote). Other anti-seizure medications that may be considered are clobazam (Onfi) and phenobarbital.
- Other alternative treatment options have been used with mixed results. These include ketogenic diet, steroids, immunoglobulins, cannabinoids, and vagus nerve stimulation.
- Levetiracetam (Keppra) can worsen seizures in nearly half of cases.
- Children with EIEE13 have frequent seizures and prolonged seizures which may need emergency medical treatment or treatment with a rescue therapy, such as diazepam rectal gel (Diastat) or another form on benzodiazepine given into the nose (intranasally) or under the tongue.
- Parents of children with EIEE13 should talk to the treating neurologist or health care provider to learn about seizure emergencies.
- Talk to the health care team about what kind of rescue therapy could be used and when to use it.
- When seizures last longer than usual or if a generalized seizure lasts too long (generally considered 5 minutes or longer), a child may need emergency medical care.
What Is The Outlook For Persons With SCN8A-Related Epilepsy?
- Epilepsy in children with SCN8A variant mutation causing EIEE13 is lifelong and resistant to medications.
- Epilepsy in children with SCN8A variant mutation causing BFIS5, in general, stops by 2 years of age.
- Many people with SCN8A variant mutation causing EIEE13 have very little to no speech, and some people gradually lose eye contact during the course of the disease. Some have autistic-like features and developmental and intellectual disabilities.
- SUDEP (sudden unexpected death in epilepsy) has been reported in 10-12% of cases with EIEE13.
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