Endocrine Abstracts

Introduction: Maternally-inherited diabetes with deafness (MIDD) is a rare form of monogenetic diabetes caused by a point mutation in mitochondrial DNA at a position 3243A>G. The syndrome is characterised by diabetes and sensoneural hearing impairment. Additional clinical features include short stature, cardiomyopathy, myopathy, renal disease, macular dystrophy, and gastrointestinal disease. The majority of patients usually require insulin therapy within 2 years and metformin is probably best avoided because of interference with mitochondrial function. The genetic change is passed down from an affected mother to all her children. However, the clinical phenotype associated with the mutation may be very heterogeneous.

Case report: We present a case of a lean 35-year-old female patient who was diagnosed with diabetes at the age of 29 years, suffering from hearing loss and migraine. She tested negative for anti-islet humoral markers (ICA, anti-GAD, and anti-IA2) and her insulin secretory reserve was partially maintained. Four years after the diagnosis, insulin was introduced to therapy. Bilateral neurosensory hearing loss was diagnosed at the age of 29 and required the use of hearing aid. There is a family history of diabetes affecting her mother, maternal uncle, and grandmother. The clinical suspicion of MIDD was confirmed by the detection of mitochondrial DNA mutation m.3243A>G in patient’s urinary epithelial cell DNA sample.

Conclusion: It is assumed that MIDD affects up to 1% of all patients with diabetes but often goes unrecognised and is misdiagnosed as either type 1 or type 2 diabetes. Although, it is not possible to predict the likely clinical course associated with this mutation due to variation in phenotype, it is important to suspect and confirm the diagnosis by the genetic testing in order to treat the patient optimally, to screen the patient for other clinical features of the syndrome and to look for the affected family members.