MATERNALLY INHERITED DIABETES-MELLITUS - THE ROLE OF MITOCHONDRIAL-DNA DEFECTS

Several studies have shown a consistent maternal effect in the transmi ssion of Type 2 diabetes (NIDDM). The mitochondrial encephalomyopathie s are a group of diseases characterized by maternal inheritance and a variety of mitochondrial DNA defects. Diabetes is a feature of some of these disorders and therefore the hypothesis arose that mitochondrial DNA mutations might play a role in patients with diabetes but no othe r features of neurological disease. Recent studies have confirmed that a specific point mutation in the gene encoding the mitochondrial tRNA for leucine segregates with diabetes and nerve deafness in families f rom the UK, Holland, France and Japan. Mitochondrial gene deletions ha ve also been reported. Affected subjects present with progressive insu lin deficiency and may fall into the broad classifications of either T ype 1 (IDDM) or Type 2 diabetes (NIDDM). Future studies are aimed at s earching for other mitochondrial gene defects in diabetes and attempti ng to explain the mechanism of hyperglycaemia by the development of ph enotypic expression systems. Although an exciting development in the g enetics of diabetes, currently described mitochondrial mutations do no t fully explain the maternal effect in the transmission of Type 2 diab etes.