DIABETES AND MITOCHONDRIAL ENCEPHALOMYOPATHY WITH LACTIC-ACIDOSIS ANDSTROKE-LIKE EPISODES (MELAS) - RADIOLABELED POLYMERASE CHAIN-REACTIONIS NECESSARY FOR ACCURATE DETECTION OF LOW PERCENTAGES OF MUTATION

A B-yr-old boy presented with muscle weakness, lactic acidemia, and in sulin-dependent diabetes mellitus (IDDM). Using PCR and restriction en zyme analysis, he was found to have the classical A3243G mitochondrial DNA (mtDNA) mutation frequently associated with mitochondrial encepha lomyopathy with lactic acidosis and stroke-like episodes (MELAS). The mutation was confirmed by sequencing muscle mtDNA. The mutation in mtD NA from muscle, lymphoblasts, and blood was clearly demonstrable by st andard methods using ethidium bromide staining. His mother also had ID DM, but no A3243G mutation could be detected in her blood or transform ed lymphoblasts using the same PCR technique. When PCR was carried out in the presence of [P-32]deoxycytidine triphosphate, subsequent autor adiography detected the presence of the mutation at low levels in mtDN A from the mother's lymphoblasts and blood. Study of the mother's musc le showed a mitochondrial myopathy, despite the fact that she was asym ptomatic. We emphasize that the increased sensitivity of radiolabeled PCR may be necessary to detect small percentages of heteroplasmic A324 3G mtDNA mutation in blood from diabetic subjects. Otherwise the incid ence of mtDNA mutations in both IDDM and non-insulin dependent diabete s may be underestimated.