Heritability of Type II (non-insulin-dependent) diabetes mellitus and abnormal glucose tolerance - a population-based twin study

To elucidate the relative importance of genetic and environmental factors o n the development of Type II (non-insulin dependent) diabetes mellitus, we examined a sample of twins (n = 606) ascertained from the population-based Danish Twin Register. Based on a standard 75 g oral glucose tolerance test and current WHO criteria we identified 62 pairs in which one or both had Ty pe II diabetes. The probandwise concordance (monozygotic: 0.50; dizygotic: 0.37) for Type II diabetes per se was not very different. When including th e twins with impaired glucose tolerance (IGT), however, the probandwise con cordance for abnormal glucose tolerance was significantly different between monozygotic (0.63) and dizygotic (0.43) twin pairs, (p < 0.01). These find ings were supported by the heritability estimates for Type II diabetes per se (26%) and for abnormal glucose tolerance (61%). The metabolic variables, insulin resistance and insulin secretion, and anthropometric variables, bo dy mass index and waist to hip ratio, known to be associated with the devel opment of glucose intolerance had a heritability of 26, 50, 80 and 6% respe ctively. This study confirms the notion of a multifactorial aetiology of Ty pe II diabetes. It supports the contribution of non-genetic aetiological co mponents in the development of Type II diabetes per se. The study also indi cates a role for genes in the aetiology of abnormal glucose tolerance. We t herefore propose that genetic predisposition is important for the developme nt of abnormal glucose tolerance. Non-genetic factors, however, might play a predominant role in controlling whether a genetically predisposed individ ual progresses to overt Type II diabetes.