Endocrine Abstracts

Maternally inherited diabetes and deafness (MIDD) is a rare form of diabetes caused by a mitochondrial DNA mutation. The condition is maternally inherited as mitochondrial DNA is practically only derived from oocytes. Patients typically have progressive insulinopenia, sensorineural hearing loss and maculardystrophy. We reported here 3 mitochondrial diabetes (two females and one male) and their families. Both of the 3 patients had diabetes, progressive loss of motor skills and sensorineural hearing loss. The average age of onset for diabetes was 34 years oldand the mean disease course was 16 years. At the beginning, they were all diagnosed as type 2 diabetes. After an average of 16 years, they were finally diagnosed as MIDD. The genetic testsshowed they all had A3243G mitochondrial DNA mutationwith different variation frequencies (12.80%, 25.00% and 13.95%, respectively). Besides, the third patient also had T16189C mitochondrial DNA mutation. Diabetes were non-insulin dependent at onset, but on average of 3 years later they started insulin therapy. In addition, patient 1 had suffered from headache for 1 month. A brain magnetic resonance imaging revealed cerebral infarction in left occipital lobe (subacute stage). So she also combined with MELAS (mitochondrialmyopathy, encephalopathy, lactic acidosis and stroke) syndrome. She has two daughters. The younger daughter was 20 years old and she had suffered from hearing loss for 1 year. She had the same mutation with her mother. But the genetic test of the asymptomatic older daughter was normal. The second patient’s daughter and sister carried the same mutation with differentvariation frequencies (77.15%, and 5.12%, respectively). But her parents and brother were normal. The third patient’s sister also suffered from diabetes and hearing loss when she was 23 years old. But she died of stroke at 30 years old. So we guessed that shesuffered from MIDD and MELAS syndrome. Even though this disease is maternal inheritance, but not all the people in this case follow the rule. It’s partly due to the diverse levels of mutated mtDNA in different tissues. The identification of monogenic forms of diabetes is difficult. However, this condition should be considered when a history of diabetes associated with both hearing loss and relevant family history.