INSULIN AUTOANTIBODIES AND HIGH-TITER ISLET-CELL ANTIBODIES ARE PREFERENTIALLY ASSOCIATED WITH THE HLA DQA1-ASTERISK-0301-DQBU-ASTERISK-0302 HAPLOTYPE AT CLINICAL ONSET OF TYPE-1 (INSULIN-DEPENDENT) DIABETES-MELLITUS BEFORE AGE 10 YEARS, BUT NOT AT ONSET BETWEEN AGE 10 AND 40 YEARS

Demographic and biological data were collected from all Caucasian Type 1 diabetic patients (n = 279) who were recruited at clinical onset by the Belgian Diabetes Registry over 34 months. The male/female ratio was significantly higher for onset between age 20 and 40 years (2.4) than before age 20 years (1.0); no age-or sex-differences were noticed in serum fructosamine concentration. Total and high concentrations of insulin autoantibodies and islet cell antibodies were preferentially associated with the HLA DQA1*0301-DQB1*0302 susceptibility haplotype. The occurrence of both types of antibodies was also correlated, irrespective of haplotype. At onset before age 10 years, the high risk genotype DQA1*0301-DQB1*0302/DQA1*0501-DQB1*0201 was more prevalent than all other DQA1-DQB1 genotypes taken together, leading to a higher prevalence of the DQA1*0301-DQB1*0302 haplotype in this age group (75%) than in the 10-39 years age group (54%). Under age 10 years, the presence of DQA1*0301-DQB1*0302 was strongly associated with insulin autoantibodies (90%) and islet cell autoantibodies (92% with 85% of high titre), whereas patients without this haplotype were less frequently positive for insulin autoantibodies (31%) or islet cell autoantibodies (38% high titre). In the group with onset at age 10-39 years, the DQA1*0301-DQB1*0302 haplotype presented a lower association with insulin autoantibodies (approximately 40%) and islet cell autoantibodies (50 to 65% high titre), prevalences which no longer differed from those in subjects lacking this haplotype. The present data demonstrate that variations in prevalence of insulin autoantibodies and islet cell autoantibodies at onset of Type 1 diabetes can result from differences in age and in the fraction of patients with the HLA DQA1*0301-DQB1*0302 haplotype. The presence of this susceptibility haplotype at onset under age 10 years identifies a sub-group of patients with more than 90% positivity for insulin autoantibodies and more than 90% positivity for islet cell autoantibodies. It is conceivable that this sub-group can be recognized in the pre-diabetic phase through screening for immunological and genetic markers.