The precise functional consequence of the m.3243 A>G mutation in tRNA-Leu (UUR) on mitochondrial function, leading to mitochondrial diabetes, is a matter of debate, but it is likely to involve 1) alteration in the ATP/ADP ratio, which is a critical determinant of insulin secretion in pancreatic beta cells, 2) functional impairment of the respiratory chain, and 3) an imbalance in the mtDNA-encoded protein amount24. The gene discussed is INS; the disease is maternally-inherited diabetes and deafness.