Low prevalence of islet autoimmunity in adult diabetes and low predictive value of islet autoantibodies in the general adult population of northern Italy

Aims/hypothesis. To assess the prevalence of islet autoimmunity in adult-on set diabetes mellitus and the predictive value of islet autoantibodies in t he general adult population of northern Italy. Methods. A sample of 2076 people aged 40 years or more participating in the population-based Cremona Study and classified in 1990 as having diabetes m ellitus, impaired and normal glucose tolerance according to WHO criteria af ter an oral glucose tolerance test, were tested for antibodies to glutamic acid decarboxylase and IA-2. Results, Increased concentrations of glutamic acid decarboxylase antibodies were found in 4 (2.8%) of 143 participants with known diabetes and none of 50 with previously unknown diabetes, 1 (0.65%) of 153 with impaired and 18 (1.0%) of 1718 with normal glucose tolerance. The increased prevalence of these antibodies in subjects with known diabetes was not statistically sign ificant. Protein tyrosine phosphatase IA-2-antibodies were found in only fo ur subjects, two of whom also had glutamic acid decarboxylase antibodies, a ll with normal glucose tolerance. After 8 years of follow-up, none of 21 no n-diabetic subjects with either glutamic acid decarboxylase or IA-2-antibod ies had developed diabetes and only a slight deterioration from normal to i mpaired fasting glucose was observed in 3 of 15 subjects with previous norm al glucose tolerance. Conclusion/interpretation. This study has shown that in northern Italy the prevalence of adult autoimmune diabetes in the general adult population is 0.19% (95% CI 0.85-0.5); that autoimmune diabetes represents only a minorit y of all cases of adult diabetes; and that islet autoantibodies are not a h igh-risk factor for diabetes development in adults with normal glucose tole rance over 8 years of follow-up.