The genetics of the glucose intolerance disorders.

Genetic heterogeneity, the concept that diabetes can have many different causes, was first suggested by the existence of rare genetic syndromes with diabetes, ethnic differences in clinical features and genetic heterogeneity of animal models. Genetic heterogeneity is now considered to be firmly established by family, twin, metabolic, immunologic and HLA disease association studies that separate idiopathic diabetes into insulin-dependent types (juvenile-onset type) and noninsulin-dependent types (maturity-onset type). Further heterogeneity is being demonstrated within each of these broad groups of disorders--within insulin-dependent diabetes using the HLA antigens and immunologic studies, and within noninsulin-dependent diabetes using such criteria as obesity, insulin response, age of onset and chlorpropamide-primed alcohol-induced flushing. This heterogeneity has major implications for the research and care of our diabetic patients since the precise etiology, risk of complications and genetic counseling are likely to vary among these different disorders that result in diabetes.