Myoclonus-dystonia and epilepsy in a family with a novel epsilon-sarcoglycan mutation

Abstract

Seizures have been reported in two families with myoclonus-dystonia due to epsilon-sarcoglycan (SGCE) mutations. We report a Norwegian family with myoclonus-dystonia and epilepsy associated with a novel SGCE mutation. All six manifesting SGCE mutation carriers had myoclonus, and dystonia was present in two patients. Sequencing of the SGCE gene in the proband identified a novel frameshift c.372delG mutation that predicts the amino acid change [p.Lys125SerfsX7] and the formation of a premature stop codon. The mutation segregated with myoclonus-dystonia in the family. The typical motor symptoms were accompanied by generalized seizures in four of six affected mutation carriers. The seizure type included febrile, absence and generalized tonic-clonic seizures. One deceased patient with severe epilepsy and myoclonus could not be tested for the SGCE mutation. Seizures are rarely observed in myoclonus-dystonia patients with SGCE mutations, and may not be a part of the phenotype. The co-occurrence of seizures and myoclonus-dystonia suggests that they are both due to the same underlying SGCE mutation. However, with epilepsy being a relatively common disorder and lack of complete co-segregation in our and previous families, it is possible that some patients suffer from two different genetic disorders. The presence of seizures and EEG abnormalities should not be considered exclusion criteria for the diagnosis of myoclonus-dystonia.