Myoclonus in fraternal twin toddlers: A French family with a novel mutation in the SGCE gene

Abstract

Myoclonus dystonia is a rare movement disorder caused by mutations in the SGCE gene on chromosome 7q21 (DYT11) encoding the epsilon-sarcoglycan. Myoclonus is present in almost all patients and affects most often neck, trunk and upper limbs. Dystonia is present in about half of the patients. The mode of inheritance is autosomal dominant with variable clinical expression and maternal imprinting. Onset is usually in childhood or adolescence. Alcohol might relieve symptoms. We present a 33 month old girl and her twin brother with disabling involuntary jerky movements during intentional tasks. Family history of this French family was positive for the paternal uncle, his two daughters and the paternal great grandfather. Sequencing of the SGCE gene revealed a novel nonsense mutation c.942C > A (p.Tyr314X) in exon 7, confirming the diagnosis of myoclonus dystonia. Treatment with valproic acid significantly reduced myoclonic episodes and ameliorated life quality.