Japanese IDDM patients have been demonstrated to have unique and different HLA associations from white patients. To elucidate the effect of HLA-associated genetic factors on the clinical heterogeneity of IDDM in Japanese people, HLA-DRB1, DQA1, and DQB1 genotypes in 88 childhood-onset Japanese IDDM patients were examined by polymerase chain reaction-sequence-specific oligonucleotide (PCR-SSO) or sequence-specific primers (SSP). Of the 88 IDDM patients, 26 (29.5%) had DRB1*0405-DQA1*0302-DQB1*0401/X (DR4-DQ4/X), 38 (43.2%) had DRB1*0901-DQA1*0302-DQB1*0303/X (DR9-DQ9/X), and 9 (10.2%) were DR4/9-DQ4/9 heterozygous in the present study (X does not contain protective alleles). Clinical heterogeneity such as age distribution at onset, prevalence and serum level of anti-GAD antibodies (GADAb), and residual pancreatic β-cell function after diagnosis were compared between patients with HLA-DR4-DQ4 and DR9-DQ9. The frequency of DR9-DQ9 genotype was significantly higher in the younger (0–10 years) than in the older (11–16 years) age-group of onset, but the frequency of DR4-DQ4 was higher in the older (11–16 years) age-group. Although no association of DR-DQ genotypes with the prevalence and serum level of GADAb was found among newly diagnosed patients, long-standing DR9-DQ9 patients had significantly higher levels of GADAb than those with DR4-DQ4. While no difference in time course of serum C-peptide (CPR) levels was detected between GADAb+ and GADAb patients, a remarkable difference was demonstrated between DR9-DQ9 and DR4-DQ4 patients. The residual pancreatic β-cell function was retained more in patients with DR4-DQ4 than in those with DR9-DQ9 at diagnosis through 12–18 months after diagnosis. These results suggest that the DR9-DQ9 genotype may induce stronger autoimmune destructive response (T-helper 1 function) against target β-cells than the DR4-DQ4 genotype does. Our findings may warrant further studies on the association of diabetogenic autoimmune response with HLA class II molecules and contribute to a clarification of interracial differences in HLA-encoded susceptibility to IDDM.

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