EpilepsiaJan 7, 2020

Range of symptoms, genetic differences, treatments, and outcomes in SCN8A-related conditions

Updated Feb 3, 2026

Abstract

Pathogenic variants in SCN8A are associated with a spectrum of neurological conditions, including severe developmental and epileptic encephalopathy (DEE).

Severe SCN8A-DEE is characterized by intractable seizures that begin in the first months of life, often presenting as prolonged focal hypomotor episodes.
Patients with severe DEE may exhibit severe cognitive and motor regression, pyramidal/extrapyramidal signs, and cortical blindness.
Electroencephalograms (EEGs) in severe cases show progressive background deterioration and multifocal abnormalities, primarily in the posterior regions.
Milder forms of SCN8A-related conditions can include intellectual disability, discrete neurological signs, and treatable epilepsy, with abnormal EEGs in about half of cases.
Some familial cases present benign infantile seizures without significant neurological deficits or cognitive impairment, often with normal interictal EEG.
Extrapyramidal features, such as dyskinesia and ataxia, are common across all patient groups, with early death reported in about 5% of severe DEE cases.

Simplified

Pathogenic variants in SCN8A have originally been described in patients with developmental and epileptic encephalopathy (DEE). However, recent studies have shown that SCN8A variants can be associated with a broader phenotypic spectrum, including the following: (1) Patients with early onset, severe DEE, developing severe cognitive and motor regression, pyramidal/extrapyramidal signs, and cortical blindness. Severe SCN8A-DEE is characterized by intractable seizures beginning in the first months of life. The seizures are often prolonged focal hypomotor and occur in clusters, with prominent vegetative symptoms (apnea, cyanosis, mydriasis), evolving to clonic or bilateral tonic-clonic manifestations. Spasm-like episodes, cortical myoclonus, and recurrent episodes of status epilepticus are also common. Electroencephalograms (EEGs) show progressive background deterioration and multifocal abnormalities, predominant in the posterior regions. (2) Sporadic and familial patients with mild-to-moderate intellectual disability, discrete neurological signs, and treatable epilepsy. EEG is abnormal in half of the cases, showing multifocal or diffuse epileptiform abnormalities. (3) Familial cases with benign infantile seizures, sometimes associated with paroxysmal dyskinesia later in life, with no other neurological deficits, normal cognition, and usually normal interictal EEG. (4) Patients without epilepsy but with cognitive and/or behavioral disturbances, or with movement disorders. Extrapyramidal features, such as dyskinesia, ataxia, and choreoathetosis are common in all groups. Early death has been reported in about 5% of the patients, most often in the subgroup of severe DEE. Premature death occurs during early childhood and often for causes other than sudden unexpected death in epilepsy. All epilepsy subgroups exhibit better seizure control with sodium channel blockers, usually at supratherapeutic doses in the severe cases. In severe SCN8A-DEE, ketogenic diet often has a good effect, whereas levetiracetam has a negative effect, if any. The familial SCN8A-related epilepsies show an autosomal dominant pattern of inheritance, whereas the vast majority of SCN8A-DEEs occur de novo.

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