Modern concepts for the prediction of type 1 diabetes.

Type 1 diabetes results from the destruction of the insulin-producing beta cells of the pancreas. The disease process is thought to be initiated by a complex interaction between genetic and environmental factors leading to a cellular and humoral autoimmune response against beta cell specific components. Over the past decade there has been important progress in identification of several diabetes specific autoantigens. The availability of recombinant antigens, most notably the enzyme glutamic acid decarboxylase (GAD) and the tyrosine phosphatase-like molecule IA-2, made it possible to develop simple, sensitive and specific radioimmunoassays for the detection of autoantibodies on a large scale. It has been shown that the combination of GAD antibodies (GADA) and IA-2 antibodies (IA-2-A) with insulin autoantibodies (IAA) can replace the conventional ICA test. This considerably facilitates screening programmes. Prospective studies in subjects with and without family history of type 1 diabetes conclusively demonstrate that the risk for type 1 diabetes is strongly correlated with the number of positive antibodies. The 5-10-years risk for type 1 diabetes varies from 0-1% in individuals with only one positive antibodies to 62-100% in subjects who were positive for three or more antibodies. Despite the identification of novel genetic markers associated with type 1 diabetes, the major histocompatibility complex, namely HLA-DQ alleles, still represents the strongest genetic risk factor. The analysis of HLA-DQ alleles may be important to discriminate between subjects at high or intermediate risk from antibody positive individuals carrying protective haplotypes. Assessment of the metabolic state using the first phase insulin response to intravenous glucose may provide additional information to predict rapid progression to diabetes. Screening for multiple antibodies is the most specific and sensitive strategy for identifying subject at risk for type 1 diabetes. Second-line genotyping or analysis of the first phase insulin response can serve as useful tool to improve the prediction of type 1 diabetes. The value of additional markers such as isotype specific autoantibodies or T-helper cells subsets measured by ELISPOT assays or FACS remains to be shown.