Early‐onset epileptic encephalopathy with myoclonic seizures related to 9q33.3‐q34.11 deletion involving STXBP1 and SPTAN1 genes

ABSTRACT We describe a 10‐month‐old boy with early‐onset epileptic encephalopathy who was found to have a hemizygous deletion in 9q33.3‐q34.11 involving STXBP1 and SPTAN1 genes. He presented at the age of 2.5 months with frequent upper extremity myoclonus, hypotonia, and facial dysmorphisms. Interictal EEG showed multifocal polyspike and wave during wakefulness and sleep. Ictal EEG revealed low‐amplitude generalized sharp slow activity, followed by diffuse attenuation. Metabolic testing was unrevealing. Brain MRI showed thinning of the corpus callosum with an absence of rostrum. This patient is the second reported case with 9q33.3‐q34.11 deletion involving STXBP1 and SPTAN1 genes associated with epileptic encephalopathy and myoclonic seizures. Larger case series are needed to better delineate this association.