Context: Mutations in mitochondrial DNA are rare etiologies of adult onset diabetes mellitus that merit identification to 1) prevent iatrogenic lactic acidosis 2) prompt appropriate screening of affected patients and their families 3) provide genetic counseling 4) provide an opportunity to investigate strategies for preventing diabetes.

Objective: To raise awareness of this rare form of adult onset non-obese diabetes mellitus so that these patients are identified and provided with appropriate care.

Patients: We describe a kindred where four of seven siblings have adult onset diabetes mellitus and sensorineural hearing loss with a confirmed genetic mutation at position 3243 in the tRNA. Two other siblings in this kindred demonstrate different phenotypes of mitochondrial disease.

Intervention: The proband was treated with Coenzyme Q10 for 1 yr.

Outcome Measures: Outcome measures included stress thallium exercise test and audiometry testing.

Results: Following one year of treatment of with Coenzyme Q10, repeat stress thallium testing demonstrated improvement in the proband's exercise tolerance from 7 min to 12 min. Audiometry testing did not demonstrate a change in the rate of decline of hearing.

Conclusion: Maternally inherited diabetes and deafness (MIDD) is a rare cause of diabetes mellitus that is important to diagnose because of the unique management issues and associated comorbidities. This work highlights clues to the identification of this rare monogenic form of adult onset diabetes.