Mutation of the CLN6 gene in teenage-onset progressive myoclonus epilepsy

Progressive myoclonus epilepsies are severe, intractable, and neurodegenerative. They afflict patients of all ages, but more commonly adolescents, and comprise the main differential diagnosis of common juvenile myoclonic epilepsy. Genetic or minimally invasive pathologic diagnoses are available for many but not all teenage-onset progressive myoclonus epilepsies. We describe a multiplex family with autosomal recessive teenage-onset progressive myoclonus epilepsy that had remained undiagnosed despite extensive genetic and pathologic testing. We describe whole exome sequencing combined with homozygosity mapping to identify the disease gene directly and diagnose the family. The affected gene is CLN6, previously known to underlie variant late-infantile and adult-onset neuronal ceroid lipofuscinoses. Combined with other recent work, our results add CLN6 to the genetic mutations causing teenage-onset progressive myoclonus epilepsy, expand the group of teenage-onset progressive myoclonus epilepsy patients who can be diagnosed by genetic testing, and extend the clinical spectrum of CLN6 mutations to include teenage-onset progressive myoclonus epilepsy. This work also exemplifies the potentiality of next-generation sequencing in the genetic identification and diagnosis of patients with neurologic diseases of unknown cause.