A NOVEL MUTATION IN THE MITOCHONDRIAL TRNA(VAL) GENE ASSOCIATED WITH A COMPLEX NEUROLOGICAL PRESENTATION

We describe a patient who presented with progressive ataxia, seizures, mental deterioration, mild myopathy, and hearing loss. A novel hetero plasmic G-to-A transition was found, affecting the acceptor stem of th e mitochondrial (mt) tRNA(Val) gene. Mutant mtDNA was 67% of total mtD NA in the muscle of the proband and was also present at low levels in the muscle of his healthy mother. It was absent in all of the numerous control DNA samples that were tested. Analysis of single muscle fiber s revealed a significantly greater level of mutant mtDNA in cytochrome c oxidase-negative fibers. Mutations of mtDNA may be responsible of n eurological syndromes that, like the case reported here, are clinicall y puzzling, and lack typical ''mitochondrial'' clues, such as elevated levels of blood lactate, overt defects of the respiratory complexes, and clinically documented maternal inheritance.