Low antioxidant content and mutation load in mitochondrial DNA A3243G mutation-related diabetes mellitus.

BACKGROUND AND PURPOSE: Diabetes mellitus (DM) is a common clinical manifestation in patients harboring mitochondrial encephalomyopathy, lactic acidosis with stroke-like episodes (MELAS)-specific A3243G mitochondrial DNA (mtDNA) mutation. However, in some MELAS family members, the presence of mtDNA mutation in the blood is not always associated with DM, and the relationship between development of DM and A3243G mtDNA mutation is not fully understood. This study evaluated the relationship between A3243G mtDNA mutation and DM in a Taiwanese family. METHODS: We analyzed the relation of genotypic and phenotypic characteristics in a 2-generation DM family associated with the A3243G mtDNA mutation. The contents of mutant mtDNA in various tissue samples of 11 family members and their serum levels of antioxidants, including protein thiols and alpha-tocopherol (vitamin E) were determined and correlated with their past history and various clinical manifestations. RESULTS: DM in 4 members of the first and second generations was associated with age and decreased serum levels of antioxidant protein thiols. In a series of studies of mutant mtDNA content in various tissues, a relatively low proportion of A3243G mutant mtDNA was noted in the elderly proband and her elderly symptomatic siblings. A low proportion of mutant mtDNA was also noted in a younger family member presenting with DM. Moreover, a significantly lower average level of protein thiols was found in the symptomatic family members compared to the asymptomatic members (2.3 +/- 0.2 vs 3.5 +/- 0.54 nmol/mg protein, p < 0.05). CONCLUSIONS: The finding of relatively lower levels of mutant mtDNA in the elderly proband and her elderly symptomatic family members indicates that DM may be a late phenotypic expression in patients harboring MELAS-specific mtDNA mutation. Decreased serum protein thiols, suggestive of increased oxidative stress, also appear to be an early sign associated with subsequent development of DM.