ClinVar

In a 38-year-old patient with a novel type of mitochondrial myopathy, Horvath et al. (2003) identified a heteroplasmic mutation, 5650G-A, in the MTTA gene. The clinical presentation and the muscle histology suggested a dystrophic muscle disease. Myotonic discharges were repeatedly observed on EMG, suggesting the diagnosis of myotonic dystrophy. Several cytochrome c oxidase-negative ragged-red fibers together with clinically observed exercise intolerance and lactic acidosis pointed to a mitochondrial origin. Single-fiber PCR showed a significantly higher rate of mutant mtDNA in ragged-red fibers. The patient's mother died at the age of 36 years from a stroke of unknown etiology. The patient developed normally until the age of 14 years, when he first noticed weakness during regular exercise at school and difficulty in climbing stairs. Proximal muscle weakness and atrophy of the lower limbs progressed slowly. At the age of 32 years he first noticed proximal weakness of the upper limbs. A pectoral lipoma was removed twice.