SCN8A is a gene that provides the blueprint for a specific sodium channel in nerve cells called Nav1.6. When this gene carries a mutation, it can cause a range of neurological conditions, most notably severe forms of epilepsy that begin in infancy. About 1% of early infantile epileptic encephalopathies are linked to SCN8A mutations.
What the SCN8A Gene Does
SCN8A belongs to a family of genes responsible for making sodium channels, which are tiny gateways that allow charged sodium atoms to flow into nerve cells. This flow of sodium is what lets neurons generate and transmit electrical signals, the basic currency of the nervous system. The specific channel SCN8A builds, Nav1.6, is found throughout the brain, spinal cord, and the nerves that connect to muscles and sensory cells responsible for touch, pain, heat, and sound.
When Nav1.6 channels work properly, they open and close with precise timing, allowing neurons to fire in controlled patterns. A mutation in the SCN8A gene disrupts that timing. Depending on the type of disruption, the consequences can range from mild developmental delays to life-threatening epilepsy.
Gain-of-Function vs. Loss-of-Function Mutations
Not all SCN8A mutations cause the same problems. The critical distinction is whether a mutation makes the sodium channel overactive (gain-of-function) or underactive (loss-of-function). This single difference shapes nearly everything about how the condition presents.
Gain-of-function mutations cause sodium channels to let in too much sodium or stay open too long, making neurons hyperexcitable. Every patient with a gain-of-function variant in published studies experienced seizures, with an average onset around 4.5 months of age. These seizures tend to be severe: focal seizures, tonic-clonic seizures (involving stiffening and convulsions), and tonic seizures are all significantly more common in this group. Gain-of-function mutations are the primary driver of developmental and epileptic encephalopathy, or DEE, the most serious form of SCN8A-related disease. Intellectual disability in this group tends to be more severe.
Loss-of-function mutations reduce sodium channel activity, making neurons less excitable than they should be. Only about 64% of people with these mutations have seizures, and when seizures do occur, they typically start much later, around 40 months on average. The seizure types also differ: absence seizures (brief lapses in awareness) and atypical seizures appear exclusively in the loss-of-function group. Some individuals with loss-of-function mutations have neurodevelopmental delays or behavioral challenges without any seizures at all. When intellectual disability is present, it tends to be milder.
Symptoms Beyond Seizures
SCN8A-related conditions involve more than epilepsy. The range of symptoms reflects how widespread Nav1.6 channels are across the nervous system.
Intellectual disability is common across the spectrum, from mild in those with loss-of-function mutations to severe in those with gain-of-function variants. Some infants develop normally at first but begin losing skills they had already acquired once seizures start, a process called developmental regression. About half of affected infants cannot perform intentional movements. Movement problems and behavioral disorders are also frequently reported.
The condition spans a true spectrum. On the milder end, some children experience benign familial infantile epilepsy, where seizures respond well to treatment and development proceeds relatively normally. On the severe end, children may face drug-resistant seizures, profound cognitive impairment, and limited mobility.
How SCN8A Conditions Are Diagnosed
There are no published clinical diagnostic criteria for SCN8A-related disorders, which means the diagnosis cannot be made based on symptoms alone. Confirmation requires genetic testing that identifies a disease-causing variant in the SCN8A gene.
For a child with early-onset epilepsy or developmental delays, testing typically starts with either a multigene epilepsy panel or exome sequencing. A multigene panel tests SCN8A alongside dozens of other genes known to cause epilepsy or intellectual disability, which is efficient for narrowing down the cause. Exome sequencing casts a wider net and has the advantage of catching recently discovered genes that panels may not yet include. Genome sequencing is another option. Single-gene testing of SCN8A alone is rarely recommended because the symptoms overlap with many other genetic conditions, making a broader approach more practical. Standard sequencing detects roughly 99% of SCN8A mutations, while gene-targeted deletion or duplication testing picks up the remaining 1%.
Treatment With Sodium Channel Blockers
For gain-of-function SCN8A epilepsy, the most promising treatment approach directly targets the underlying problem. Because the mutations cause sodium channels to be overactive, medications that block sodium channels can counteract the excess electrical activity. This is one of the clearest examples of precision medicine in epilepsy: the treatment is matched to the molecular cause.
Carbamazepine and its derivative oxcarbazepine have proven useful for many patients and are considered first-line options. These drugs bind to sodium channels and reduce the flow of sodium into neurons, lowering their excitability. Some patients achieve seizure-free periods on these medications. For those who don’t respond adequately, high-dose phenytoin, another sodium channel blocker, has shown effectiveness. In one reported series, three out of four severely affected patients became seizure-free on high doses of phenytoin, though seizures returned when the medication was tapered.
Treatment outcomes vary widely. Some children respond dramatically to the right medication, while others continue to have difficult-to-control seizures despite multiple drug trials. Early identification of the mutation type can help guide treatment choices more quickly, potentially sparing families months of trial and error with medications that are unlikely to help.
Long-Term Outlook and Risks
Most published patients with SCN8A-related conditions are still in the first two decades of life, so long-term data remains limited. In a review of 190 patients, 10 had died, putting the overall mortality rate at 5.3%. Seven of the ten deaths occurred in early childhood. The most common cause of death was not sudden unexpected death in epilepsy (SUDEP), as researchers initially hypothesized, but rather a progressive worsening of the neurological condition that left children vulnerable to respiratory infections and breathing difficulties.
Three of the ten deaths were attributed to probable or definite SUDEP, a rate that does not appear elevated compared to other forms of developmental and epileptic encephalopathy. Across the broader group of sodium channel epilepsies, published reports suggest a mortality rate of approximately 10 to 15% by age 20.
Developmental outcomes depend heavily on the type of mutation, the severity of seizures, and how early effective treatment begins. Whether early intervention can meaningfully alter the developmental trajectory remains an open and urgent question for families and researchers. For children on the milder end of the spectrum, particularly those with benign familial infantile epilepsy linked to gain-of-function variants, the outlook is substantially better, with seizure control often achievable and development proceeding closer to typical milestones.