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OBJECTIVE—We sought to study the prevalence of autoantibodies to various islet cell antigens in the background population of two neighboring countries with a sixfold difference in the incidence of type 1 diabetes. RESEARCH DESIGN AND METHODS—Serum samples were obtained from 3,652 nondiabetic schoolchildren in Finland and from 1,988 schoolchildren in the adjacent Karelian Republic of Russia. The Karelian children were divided into three groups (Finns/Karelians, Russians, and others) based on the ethnic background of their mother. The samples were analyzed for islet cell antibodies (ICAs), insulin autoantibodies (IAAs), GAD antibodies (GADAs), and the tyrosine phosphatase-like insulinoma antigen 2 (IA-2A) protein and HLA class II genotypes. RESULTS—The frequency of ICAs, IAAs, and GADAs did not differ significantly between the Karelian (3.5, 0.6, and 0.9%, respectively) and Finnish children (2.8, 0.9, and 0.5%, respectively). Similarly, the frequency of multiple (≥2) autoantibodies was similar in both countries (0.5 vs. 0.6%). The frequency of IA-2A was, however, four times higher in Finland (0.6 vs. 0.15% in Russian Karelia; P = 0.03). There were no significant differences in autoantibody prevalence among the three ethnic groups in Russian Karelia. There was a falling frequency of GADAs and of positivity for multiple autoantibodies along with decreasing HLA-conferred disease susceptibility among the Finnish schoolchildren. CONCLUSIONS—These data indicate that β-cell autoimmunity among schoolchildren is as frequent in Russian Karelia as in Finland, although the incidence of clinical type 1 diabetes is six times higher in Finland. However, in contrast to this general trend, IA-2As were more common in Finland. Since IA-2As usually appear late in the preclinical process, this suggests that progressive β-cell autoimmunity is more rare in Russian Karelia.

Recent studies have suggested that vitamin D deficiency may increase the risk of type 1 diabetes (1). In Finland, the incidence of type 1 diabetes is the highest in the world, while in the neighboring Karelian Republic of Russia, the incidence is approximately one-sixth that in Finland, despite no difference in HLA-conferred susceptibility (2). Thus, the reason(s) must be linked to environmental factors. We assessed vitamin D status in the Russian Karelian and Finnish populations to determine whether vitamin D could play a role in the huge difference observed in diabetes incidence. The geographical location in terms of daily sunlight exposure is …