Early Infantile Epileptic Encephalopathy 13; EIEE13; SCN8A Encephalopathy

SCN8A-related Epilepsy with Encephalopathy is a rare autosomal-dominant genetic disorder affecting infants, characterized by recurrent seizures of multiple types, along with intellectual disability. These seizures are described as refractory, meaning that they generally do not respond to or improve with treatment.

While the condition is often evident at birth, some affected infants will exhibit apparently normal development until the onset of seizures, at which point the child will begin to regress from both physical and cognitive standpoints. The severity of intellectual impairment associated with SCN8A-related epilepsy encephalopathy varies from mild to severe.

As the name indicates, the condition is caused by a mutation on the SCN8A gene. The relationship between the genetic anomaly and its distinct effects on intellectual and physical development are poorly understood; some research indicates that these symptoms are more closely correlated with the brain damage resulting from the seizures, rather than the mutation itself.

Diagnostic testing:

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  Molecular genetic testing is required to confirm mutation on the SCN8A gene.

Physical findings: Common symptoms include:

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  Seizures of multiple types (absence, tonic-clonic, convulsive);

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  Intellectual disability including autistic features;

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  Motor disorders;

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  Muscle weakness; and

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  Sleep disorders.

ICD-9: 345.81

ICD-10: G40.803

Affected infants will begin exhibiting symptoms between birth and 18 months of age, with median onset at 4 months. Treatment is supportive; people with SCN8A-related epilepsy with encephalopathy can survive to adulthood with appropriate care.

In about 10% of identified cases, the infant dies without any obvious cause, a phenomenon known as sudden unexpected death in epilepsy (SUDEP).

SCN8A-related epilepsy with encephalopathy typically does not respond to traditional anticonvulsive medication. Antiepileptic drugs that block sodium channels (e.g., phenytoin, valproate, carbamazepine) have shown promise in some studies.

Suggested MER for Evaluation:

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  Clinical history and examination that describes the diagnostic features of the impairment;

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  Genetic testing confirming mutation of the SCN8A gene; and

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  Imaging reports such as CT scan or MRI scan.

Suggested Listings for Evaluation:

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