Mitochondrial disease: an uncommon but important cause of diabetes mellitus.

Mitochondrial diseases are rare, heterogeneous conditions affecting organs dependent on high aerobic metabolism. Presenting symptoms and signs vary depending on the mutation and mutant protein load. Diabetes mellitus is the most common endocrinopathy, and recognition of these patients is important due to its impact on management and screening of family members. In particular, glycemic management differs in these patients: the use of metformin is avoided because of the risk of lactic acidosis. We describe a patient who presented with gradual weight loss and an acute presentation of hyperglycemia complicated by the superior mesenteric artery syndrome. His maternal history of diabetes and deafness and a personal history of hearing impairment led to the diagnosis of a mitochondrial disorder. Learning points: •• The constellation of diabetes, multi-organ involvement and maternal inheritance should prompt consideration of a mitochondrial disorder. •• Mitochondrial encephalomyopathy, lactic acidosis, stroke-like episodes (MELAS) and maternally inherited diabetes and deafness (MIDD) are the most common mitochondrial diabetes disorders caused by a mutation in m.3243A>G in 80% of cases. •• Metformin should be avoided due to the risk of lactic acidosis. •• There is more rapid progression to insulin therapy and higher prevalence of diabetic complications compared to type 2 diabetes. •• Diagnosis of a mitochondrial disorder leads to family screening, education and surveillance for future complications. •• Superior mesenteric artery syndrome, an uncommon but important cause of intestinal pseudo-obstruction in cases of significant weight loss, has been reported in MELAS patients.