HLA Class II Variation in Indigenous Populations from Thailand

We have a lysed the distribution of class II alleles in five populations from Thailand, by PCR amplification of second exon of the DRBl, DQA1, DQB1 and DPB1 loci and typing using non adioactive sequence-specific oligonucleotide probes. Extensive allelic variation was found at all four loci examined, but no new alleles were identified. The allele frequency distribution was very similar among the Thai populations, indicative of limited amounts of genetic divergence among the different populations examined. A phylogenetic a lysis was conducted using the allele frequency data for each locus to study the relationships between Thai populations, other Asian populations and populations from other parts of the world. In the phylogenetic trees for three of the four loci, the Thai populations cluster with other Asian populations, supporting the similarity among Asian populations. The branch lengths of the phylogenetic trees are substantially longer for the DQA1 and DQB1 loci, as compared to DRB1 and DPB1 loci. In particular, the length of branches separating populations on different continents are more pronounced for the DQA1 and DQB1 loci.