Mitochondrial myopathy with predominant respiratory dysfunction in a patient with A3243G mutation in the mitochondrial tRNALeu(UUR) gene

We report a patient with the A3243G point mutation of mitochondrial DNA (mtDNA) who presented with severe impairment of respiratory function and only mild involvement of limb muscles. This 55-year-old woman had a history of repeated episodes of respiratory failure unexplained by lung disease or central nervous system lesions. Needle electromyography suggested myopathy and muscle biopsy showed many ragged-red fibers. Molecular analysis of mtDNA in blood and muscle cells showed an A3243G point mutation in the tRNA(Leu(UUR)) gene; the percentages of mutant mtDNA in blood and muscle cells were 65% and 71%, respectively. These findings suggest that mitochondrial myopathy should be considered as a cause of respiratory failure due to neuromuscular disorders, and that pure myopathy with predominant respiratory dysfunction is one of the heterogeneous phenotypic features associated with the A3243G point mutation of mtDNA.