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Strategies to resolve B*18 alleles which carry a deletion in intron 1 close to the 50 end of exon 2 relative to other HLA-B alleles or a null allele mutation in exon 1 and to resolve ambiguities among allele combinations including B*18 are described. B*18 allele frequencies from volunteer donors recruited for two hematopoietic stem cell registries show the presence of two alleles, B*180101 and B*1802, in a population from Singapore and only B*180101 in African-Americans. [ABSTRACT FROM AUTHOR]

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.

Based on unusual probe hybridization patterns, two human leukocyte antigen (HLA)-A, five HLA-B, and two HLA-C alleles (A*240208, A*3211Q; B*1822, B*3938Q, B*4606, B*4607N, B*5139; Cw*0321, Cw*0734) were identified in individuals from the Singapore Bone Marrow Donor Program and Singapore Cord Blood Bank. Eight of the nine alleles encode amino acid substitutions altering the antigen-binding region including three alleles with changes altering a cysteine at codon 164 (A*3211Q, B*3938Q, B*4607N). This substitution either eliminates a key disulfide bond or results in a stop codon, both likely affecting the expression of the HLA molecules. Only one allele (A*240208) carries a synonymous substitution.