5 Questions Answered About Rare SCN8A-related Epilepsy
Epileptologist explains symptoms, causes, diagnoses of SCN8A
February 9 marks SNC8A Awareness Day worldwide. A rare cause of refractory epilepsy, SCN8A mutations have now been described in over 250 patients worldwide and several receive their care at Cook Children’s. To raise awareness of this rare genetic cause of epilepsy, Dr. M. Scott Perry MD, Medical Director of Neurology and Director of the Genetic Epilepsy Clinic at Cook Children’s shares basic information about the disorder.
What are some of the symptoms of SCN8A-related epilepsy? Children with SCN8A epilepsy often present early in life with developmental delays which may occur from birth or may arise shortly after seizure onset. Seizures often begin in the first 18 months of life (average 4 months) with a variety of seizures types including infantile spasms, generalized tonic-clonic, myoclonic, focal-onset, and absence seizures amongst others. Seizures are often difficult to control in 70 percent of patients. Movement disorders such as myoclonus (quick jerk-like movements), dystonia (fixed abnormal posturing of the limbs), ataxia (unsteady, incoordination), and choreoathetosis (constant, irregular, writhing movements) are also common manifestations. Mild to severe intellectual disability is common and many patients demonstrate autistic symptoms.
What is the cause of SCN8A-related epilepsy? Dr. Michael Hammer, Ph.D., first discovered the SCN8A gene as a cause of epilepsy when he was searching for the cause of his daughter Shay’s epilepsy. Shay unfortunately passed away from Sudden Unexplained Death in Epilepsy (SUDEP), but we continue to celebrate her life and raise awareness of this syndrome on her birthday (2/9) each year. To learn more about Dr. Hammer and Shay’s story, click here.
SCN8A is a gene which encodes a sodium channel found throughout the nervous system and highly expressed in the brain. Sodium channels are in part responsible for generating the electricity of the brain. In children with mutations in SCN8A, sodium channels can open too easily or stay open too long which produced increased electricity and tendency for seizures. Mutations in SCN8A are almost always de novo, meaning they occur spontaneously and were not inherited from the parents. SCN8A mutations cause an autosomal dominant disorder, meaning only one gene mutation is required for symptoms of the disorder to arise.
How is SCN8A-related epilepsy diagnosed? Diagnosis is made using genetic testing in patients with appropriate clinical features. MRI is often normal or may show some global atrophy. EEGs often show slowing of the background rhythm with multifocal spikes.
Is there a treatment for SCN8A-related epilepsy? Unfortunately, there is not yet a cure for SCN8A-related epilepsy, however, certain sodium channel drugs (for example, carbamazepine, phenytoin, oxcarbazepine) have demonstrated more favorable responses for seizure control. Many families have reported levetiracetam to worsen seizures. Aggressive control of seizures with a clear rescue plan for prolonged seizures is important. Other manifestations such as spasticity and movement disorders can be managed to some degree with medications and therapy.
What other problems might be found in patients with SCN8A-related epilepsy? Anecdotally, patients with SCN8A mutations are often reported to have exaggerated startle response or excessive jitteriness in infancy. Some patients may have small head size (microcephaly), visual impairment, hearing impairment, and autonomic dysfunction (for example trouble maintaining temperature or steady heart rate). As more patients with SCN8A are discovered, the characteristics of the syndrome continue to evolve.
For more information about SCN8A and SCN8A Awareness Day, visit http://www.scn8aawarenessday.net/.
Get to know M. Scott Perry, M.D.
I joined the Neurosciences Program of Cook Children's in 2009 as a pediatric epileptologist, then served as the Medical Director of the Epilepsy Monitoring Unit and Tuberous Sclerosis Complex clinic before assuming the role of Medical Director of Neurology in 2016. My clinical and research interests focus on the treatment of childhood onset epilepsy, specifically those patients with uncontrolled epilepsy or those for which the cause has not been determined. I have an intense interest in the use of surgical therapies to treat and cure epilepsy. The majority of my research has investigated the use of multimodal imaging techniques to localize seizure onset, as well as the description of patient and disease characteristics that predict favorable outcomes from surgical therapies. The pool of candidates which may benefit from surgical therapy continues to expand and I came to Cook Children's specifically because the staff of the Epilepsy Monitoring Unit and Comprehensive Epilepsy Program were dedicated to improving the care of children with epilepsy through cutting-edge techniques, research, and concern for their patients' well-being. Click to learn more.