SCN2A Mutation Causing Benign Neonatal Infantile Seizures and Later Episodic Ataxia

The 2.5 years old boy presented with clusters of tonic and hypomotor seizures starting at age 7 days. The seizures did not respond to a treatment with vitamin B₆, phenobarbitone, levetiracetam, and topiramate. He became seizure free with 7 months after adding oxcarbazepine. The initial EEGs were normal and bioccipital sharp waves were seen only once at age 7.5 months. After several normal controls, right central benign sharp waves were observed from 17 months of age. The patient initially presented with a marked muscular hypotonia with only slow improvement. The development was slightly retarded. MRIs at age 3 weeks and 6 months were normal, as was the brought neurometabolic work-up. The parents reported an inability to move in the context of a febrile infection at 15 months of age. Attacks of an episodic ataxia started at 22 months of age and occurred once or twice a month since then. In the morning, the gait of the complete responsive child is unsteady. The severity of symptoms increases during the day until the boy is unable to stand or walk. The attacks last at least for hours and usually the whole day.

Genetic testing revealed an SCN2A mutation c.788 C >T; p.A263V that has previously been described¹ in a child with almost identical symptoms (but in addition attacks with pain). A gain of function was revealed by physiological analysis. In this described case, trials with phenytoin, valproate, acetazolamide, oxcarbazepine, carbamazepine, gabapentin, clobazam, levetiracetam and topiramate failed to control the attacks. Both the cases demonstrate the variability of phenotypes in sodium channel mutations and the link of seizures and movement disorders.

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1 Liao Y, Anttonen AK, Liukkonen E, et al. SCN2A mutation associated with neonatal epilepsy, late-onset episodic ataxia, myoclonus, and pain. Neurology 2010;75(16):1454–1458