Muscle histopathology in diabetes mellitus associated with mitochondrial tRNA(Leu(UUR)) mutation at position 3243.

Diabetes mellitus associated with 3243 mitochondrial tRNA(Leu(UUR)) mutation (DM-Mt3243) is a subtype of the mitochondrial multisystem syndromes, usually lacking myopathy. Muscle biopsies were obtained from 5 patients with diabetes and one patient with impaired glucose tolerance, all possessing the 3243 mutation without hallmarks of MELAS. The specimens were subjected to histochemical, biochemical, and genetic analysis. Ragged-red fibers were seen in 4 of the 6 patients (67%), and focal cytochrome c oxidase deficiency in 3 (50%). Strongly succinate dehydrogenase-reactive blood vessels was found in 5 patients (83%). The histochemical signs were present even when the mutant percentage was very low. The percentage of mutant DNA was almost always higher in muscles than in leukocytes. The combination of allele specific PCR amplification and PCR-RFLP method was useful to evaluate the mutant proportion. The mutant percentage in muscle was under 50% in 5 (83%) patients. Mitochondrial enzyme activity was deficient only in one patient. This study presents the detailed muscle histopathology in the DM-Mt3243 group. Abnormal histopathologic findings seemed similar to those noted in MELAS. However, mutant percentage in muscles was lower than that of MELAS, and respiratory chain enzyme activity was well preserved.