Low prevalence of antibodies to GAD65 in a 50- to 74-year-old general Dutch population - The Hoorn study

OBJECTIVE -- To assess the prevalence of antibodies to GAD65 (GAD65-A) in relation to glucose tolerance disturbances and to blood glucose-lowering therapy in a general Dutch population. RESEARCH DESIGN AND METHODS -- A population sample of 2.350 Dutch subjects, age 50-74 years, agreed to undergo an oral glucose tolerance test (OGTT). They were classified as having normal glucose tolerance, impaired glucose tolerance, newly detected diabetes, or known diabetes. GAD65-A levels were measured in serum by means of a standardized radioligand assay and subsequently were expressed as indexes. The prevalence rates were defined as the proportions of individuals of each category of glucose tolerance exceeding the value of the index at the 99th percentile of the entire study population. RESULTS -- The prevalence rates and the 95% CIs of GAD65-A were 0.7% (0.4-1.20/6) in cases of normal glucose tolerance, 2.4% (0.9-5.3%) in impaired glucose tolerance. 0% (0-3.3%) in newly detected diabetes. according to the World Health Organization (WHO) criterial and 3.5% (0.7-10.0%) in known diabetes. A total of 2 out of 3 subjects with GAD65-A indexes above the 99th percentile and 10 out of 18 subjects with GAD65-A indexes above the 85th percentile received insulin therapy for their diabetes, which showed an association between GAD65-A and insulin therapy. CONCLUSIONS -- Low prevalence rates of latent autoimmunity to GAD were found in 50- to 74-year-old Dutch subjects with normal and abnormal glucose tolerance, and GAD65-A was associated with insulin use in known diabetic subjects.