Twin studies in diabetes mellitus.

Twin studies are a valuable way of determining the relative significance of genetic and environmental factors in the aetiology of disease. In diabetes mellitus, they are of importance, since the aetiologies of Type 1 (insulin-dependent) and Type 2 (non-insulin-dependent) diabetes mellitus are probably different. However the results of twin studies have not always been reliable. Strict adherence to methodological guidelines is necessary to ensure the validity of the results that are obtained. These guidelines relate to ascertainment of a twin sample, confirmation of zygosity, and effects of sampling. Critical review of twin studies in diabetes performed to date imply provisionally a very strong genetic input to the aetiology of Type 1 diabetes. In Type 2 diabetes genetic and environmental factors are probably of equal importance.