SPORADIC MERRF MELAS OVERLAP SYNDROME-ASSOCIATED WITH THE 3243-TRNA(LEU(UUR)) MUTATION OF MITOCHONDRIAL-DNA/

We studied a patient with a mitochondrial encephalomyopathy characteri zed by the presence of all the cardinal features of both myoclonic epi lepsy and ragged-red fibers (MERRF) and mitochondrial encephalomyopath y, lactic acidosis, and strokelike episodes (MELAS) syndromes. Muscle biopsy showed ragged-red fibers (RRF). Some RRF were cytochrome c oxid ase (COX)-negative while some others stained positive for COX. Muscle biochemistry revealed defects of complexes I and IV of the respiratory chain. Both muscle and blood mitochondrial DNA from the patient showe d the presence of the mutation at nucleotide position 3243 in the tRNA (Leu(UUR)) gene and the absence of point mutations related to MERRF sy ndrome. The proportions of mutant mtDNA were 70% in muscle and 30% in blood. The mutation was absent in blood from all maternal relatives, i n hair follicles from the mother, and in muscle from one sister of the proband. Therefore, there was no evidence of maternal inheritance. (C ) 1996 John Wiley & Sons, Inc.