Mitochondrial myopathy with dystrophic features due to a novel mutation in the MTTM gene

: A 61‐year‐old woman with a 5‐year history of progressive muscle weakness and atrophy had a muscle biopsy characterized by a combination of dystrophic features (necrotic fibers and endomysial fibrosis) and mitochondrial alterations [ragged‐red, cytochrome c oxidase (COX)‐negative fibers]. Methods : Sequencing of the whole mtDNA, assessment of the mutation load in muscle and accessible nonmuscle tissues, and single fiber polymerase chain reaction. Results : Muscle mitochondrial DNA (mtDNA) sequencing revealed a novel heteroplasmic mutation (m.4403G>A) in the gene ( MTTM ) that encodes tRNA Met . The mutation was not present in accessible nonmuscle tissues from the patient or 2 asymptomatic sisters. Conclusions : The clinical features and muscle morphology in this patient are very similar to those described in a previous patient with a different mutation, also in MTTM , which suggests that mutations in this gene confer a distinctive “dystrophic” quality. This may be a diagnostic clue in patients with isolated mitochondrial myopathy. Muscle Nerve 50:292–295, 2014