Age of onset possibly associated with the degree of heteroplasmy in two male siblings with diabetes mellitus having an A to G transition at 3243 of mitochondrial DNA

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We describe two male siblings with diabetes mellitus caused by mitochondrial 3243 mutation. The level of heteroplasmy in peripheral blood leucocytes was determined by a last-cycle hot PCR method. The younger brother, who had 39% heteroplasmy, developed diabetes at age of 25, and demonstrated a lean body habitus and blunted insulin secretion. The elder brother, who had 22% heteroplasmy, was diagnosed at the age of 42. The younger brother showed a higher increment of serum lactate after exercise. In these siblings the level of heteroplasmy in their peripheral blood leucocytes appeared to be associated with age of onset of diabetes.