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During 2005, a total of 174 cord blood units with their paired maternal samples from the Singapore Cord Blood Bank were typed for HLA-A, -B, -C at intermediate resolution and DRB1 at allelic resolution. Analysis of allele segregation in mother and child assigned 185 different four locus (HLA-A, -B, -C, -DRB1) haplotypes in Chinese, 66 in Malays, and 34 in Asian Indians. Very few four locus haplotypes were shared among population groups. To evaluate the frequencies of four locus haplotypes, the Expectation Maximization algorithm was used with HLA assignments from 536 unrelated Chinese volunteers from the Singapore Bone Marrow Donor Program registry. The paired maternal and cord blood study identified 75 different B-C associations in Chinese, 52 in Malays, and 24 in Asian Indians. Common B-C associations may be shared among population groups; for example, B*4001g-Cw*0702g was common in Chinese and Malays, whereas B*1502g-Cw*0801g and B*3501g-Cw*0401g were found in all three groups. The high diversity of four locus haplotypes originates from multiple combinations of both HLA-A and -DRB1 alleles with each B-C haplotype.

HLA-A30 is one of the serologically characterized specificities and has been known to exhibit different haplotypic associations in different ethnic groups. This study reveals the presence of two HLA-A*30 alleles, A*3001 (31/48; 64.6%) and A*3004 (17/48; 35.4%), with each allele existing as a distinct haplotype in the Korean population. One haplotype, A*3001-Cw*0602-B*1302-DRB1*0701-DQA1*02-DQB1*02, found in 77.4% of A*3001-positive individuals is likely identical to the haplotype previously identified by serology in Asians and European Caucasians. A second haplo-type, A*3004-Cw*0802-B*1401-DRB1*0404-DQA1*03-DQB1*0402, found in 64.7% of A*3004-positive individuals has not previously been described. Conserved and distinct haplotypic associations of the two A*30 alleles imply that the two haplotypes may have evolved separately and are relatively new in this population.