HLA-associated relative risks of type 1 (insulin-dependent) diabetes mellitus were analysed in population-based Swedish patients and controls aged 0-34 years. The age dependence of HLA-associated relative risks was assessed by likelihood ratio tests of regression parameters in separate logistic regression models for each HLA category. The analyses demonstrated an attenuation with increasing age at onset in the relative risk for the positively associated DQB1*0201-A1*0502/B1*0302-A1*0301 (DQ2/8) genotype (P = 0.02) and the negatively associated DQB1*0602-A1*0102 (DQ6.2) haplotype (P = 0.004). At birth, DQ6.2-positive individuals had an estimated relative risk of 0.03, but this increased to 1.1 at age 35 years. Relative risks for individuals with DQ genotype 8/8 or 8/X or DQ genotype 2/2 or 2/X, where X is any DQ haplotype other than 2, 8 or 6.2, were not significantly age-dependent. An exploratory analysis of DQ haplotypes other than 2, 8 and 6.2 suggested that the risk of type 1 diabetes increases with age for DQB1*0604-A1*0102 (DQ6.4) and that the peak risk for the negatively associated DQB1*0301-A1*0501 haplotype is at age 18 years. There was also weak evidence that the risk for DQB1*0303-A1*0301 (DQ9), which has a positive association in the Japanese population, may decrease with age. We speculate that HLA-DQ alleles have a significant effect on the rate of beta cell destruction, which is accelerated in DQ2/8-positive individuals and inhibited, but not completely blocked, in DQ6.2-positive individuals.

The phenotype and gene frequencies of HLA class II alleles were studied in the North‐eastern Thai population. Blood samples were collected from 100 unrelated healthy North‐eastern Thais. The HLA‐DRB1 and DQB1 genes were typed using the polymerase chain reaction – sequence specific primer (PCR‐SSP) and polymerase chain reaction – sequence specific oligonucleotide probe (PCR‐SSO) techniques. Twenty‐six HLA‐DRB1 and 11 DQB1 alleles were found in this population. DRB1*1202, 1502, 0405 and DQB1*0502/0504, 0301/0304 alleles were commonly found. Linkage disequilibrium analysis suggested the existence of 13 DR‐DQ haplotypes. The DRB1*1502‐DQB1*0501 haplotype was the most common. The DRB1*1106‐DQB1*0301/0304 haplotype was found only in North‐eastern Thais and not in other Thai populations. Comparative analysis of the HLA‐DR/DQ alleles revealed differences in the distributions of these alleles amongst different ethnic groups. Interestingly, the distributions of HLA class II alleles in Central Thai, North‐eastern Thai and Southern Chinese populations are similar. However, it appears that the distribution in the Central Thais is a mixture of those in Southern Chinese and North‐eastern Thais, suggesting the existence of Thai–Chinese admixtures in the Central Thai population. This study provides basic information for further studies of the MHC in anthropology, organ transplantation and disease susceptibility in the North‐eastern Thai population.

The phenotype and gene frequencies of HLA class II alleles were studied in the North-eastern Thai population. Blood samples were collected from 100 unrelated healthy North-eastern Thais. The HLA-DRB1 and DQB1 genes were typed using the polymerase chain reaction--sequence specific primer (PCR-SSP) and polymerase chain reaction--sequence specific oligonucleotide probe (PCR-SSO) techniques. Twenty-six HLA-DRB1 and 11 DQB1 alleles were found in this population. DRB1*1202, 1502, 0405 and DQB1*0502/0504, 0301/0304 alleles were commonly found. Linkage disequilibrium analysis suggested the existence of 13 DR-DQ haplotypes. The DRB1*1502-DQB1*0501 haplotype was the most common. The DRB1*1106-DQB1*0301/0304 haplotype was found only in North-eastern Thais and not in other Thai populations. Comparative analysis of the HLA-DR/DQ alleles revealed differences in the distributions of these alleles amongst different ethnic groups. Interestingly, the distributions of HLA class II alleles in Central Thai, North-eastern Thai and Southern Chinese populations are similar. However, it appears that the distribution in the Central Thais is a mixture of those in Southern Chinese and North-eastern Thais, suggesting the existence of Thai-Chinese admixtures in the Central Thai population. This study provides basic information for further studies of the MHC in anthropology, organ transplantation and disease susceptibility in the North-eastern Thai population.