A mitochondrial DNA tRNA(Val) point mutation associated with adult-onset Leigh syndrome.

Subacute necrotizing encephalomyelopathy (Leigh syndrome) is associated with a number of mitochondrial DNA (mtDNA) abnormalities. We studied a family with maternally inherited encephalomyelopathy. Two siblings developed adult-onset Leigh syndrome. Muscle biopsy specimens showed enhanced succinic dehydrogenase activity and cytochrome oxidase-negative fibers. We sequenced the ATPase- and transfer RNA (tRNA)-encoding genes of mtDNA and identified a novel mtDNA valine tRNA mutation at base pair 1644. This transversion was heteroplasmic in blood and muscle in all individuals studied, and the proportion of mutant mtDNA correlated with disease severity. This is the first heteroplasmic transversion within a mtDNA tRNA gene and the second pathogenic mtDNA tRNA(Val) mutation to be associated with human disease.