Diabetes and deafness (DAD) or maternally inherited diabetes and deafness (MIDD) or mitochondrial diabetes is a subtype of diabetes which is caused from a mutation in mitochondrial DNA, which consists of a circular genome. It is associated with the genes MT-TL1, MT-TE, and MT-TK. The point mutation at position 3243A>G, in gene MT-TL1 encoding tRNA leucine 1, is most common. Because mitochondrial DNA is contributed to the embryo by the oocyte and not by spermatozoa, this disease is inherited from maternal family members only. As indicated by the name, MIDD is characterized by diabetes and sensorineural hearing loss. Some individuals also experience more systemic symptoms including eye, muscle, brain, kidney, heart, and gastrointestinal abnormalities, similar to other mitochondrial diseases.