Aspartic acid at position 57 of the HLA‐DQβ chain in insulin‐dependent diabetes mellitus: An association with one DRw9–DQw9 subtype in the Chinese population

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Abstract
Eighteen unrelated Chinese patients with insulin‐dependent diabetes mellitus (IDDM) were analyzed for HLA Class II genes using a variety of molecular biological techniques including restriction fragment length polymorphism (RFLP), polymerase chain reaction with allele‐specific oligonucleotides (PCR‐ASO) and direct DNA sequencing. The high frequency of DR3/DR4 heterozygotes found in the Chinese with IDDM strengthens the importance of this combination of haplotypes in IDDM susceptibility since it is present in two genetically distant populations ‐Chinese and Caucasians. The frequency of DRw9, a rare allele in the Caucasian population, is much higher in the Chinese. Moreover, the DQβ chain linkage of DRw9 was different in IDDM patients compared with control subjects. In contrast with previous results, codon 57 of the DQβ chain was aspartic acid in DRw9 Chinese IDDM patients. Furthermore, one particular DRw9–DQw9 haplotype may be associated with IDDM susceptibility in the Chinese population.