Mutations in mitochondrial DNA are a rare cause of diabetes. Mitochondrial DNA is a circular molecule that contains 37 genes that are passed on from the mother to her offspring. Paternal transmission of mitochondrial DNA is thought not to occur, because after fertilization, the fertilized egg destroys mitochondria derived from the sperm.

Diabetes and hearing loss are associated with a point mutation of mitochondrial DNA. The mutation occurs in the gene that encodes tRNA leucine, leading to the substitution of guanine for adenine (A?G).

The tRNA Leu 3243 mutation was originally identified in patients with the MELAS syndrome (mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like syndrome); however, diabetes is not part of this syndrome, suggesting that this mitochondrial mutation may be expressed as different phenotypes

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