[Genetic diagnosis of diabetes mellitus]

NIDDM is likely to have a major genetic component in view of the different prevalence between ethnic groups, the familial clustering, and the high concordance in monozygotic twins. Linkage analysis of extended pedigrees of patients with maturity-onset diabetes of the young (MODY) identified the glucokinase gene mutations. Specific phenotypes have also led to the discovery of the insulin gene mutations in patients with high insulin or proinsulin levels, to the insulin receptor mutations in patients with marked insulin resistance, and to the mutations in mitochondrial DNA associated with deafness and maternal inheritance. These four types of diabetogenic gene mutations account for only a minor proportion of NIDDM. Direct screening for mutations in candidate genes with single-strand conformation polymorphism or heteroduplex screening or with direct sequencing in the diabetic patients with the appropriate pathophysiological abnormality can be a successful strategy. Genetic diagnosis provides clear definite diagnosis and specific therapies, such as IGF-1 for the insulin receptor mutations and coenzyme Q10 for the mitochondrial gene mutations.