1024-LBP: HLA DPA1∼DPB1 allele-level and motif-level haplotype frequencies of four US populations

Abstract

Aim Recent data show that DP matching plays an important role in hematopoietic cell transplantation. Our previous work demonstrated that in European Americans haplotypic associations for the DP heterodimer are determined by near complete linkage disequilibrium between amino acid motifs on DPA1 (pos 31) and DPB1 (pos 85–87). We aimed to generate motif and allele-level haplotype frequencies (HF) for four race groups to extend these insights to minorities. Methods We calculated DPA1∼DPB1 HF at allele and motif level from 16,802 Be the Match Registry® members typed by DNA methods, resolving phase, allelic and motif ambiguity using expectation maximization. Motif frequencies were calculated for position 31 on DPA1 and positions 85–87 on DPB1, which play a critical role in the P1 pocket of the peptide binding region. Normalized linkage disequilibrium (LD) was calculated on each haplotype (D′) and globally (Wn) for each population. Results The top three allele-level haplotypes in all populations account for over 66% of the HF, with DPA1∗01:03 ∼ DPB1∗04:01 most common in the Caucasian (CAU), Asian Pacific Islander (API) and Hispanic (HIS) populations and DPA1∗02:02 ∼ DPB1∗01:01 in the African American (AFA) population. Wn for DPA1∼DPB1 allele associations for CAU, HIS, API, and AFA populations was .55, .45, .49, and .52 respectively. At the motif level there were only four possible haplotypes. M ∼ GPM and Q ∼ EAV were the two most common in every population. M ∼ GPM was the most common in CAU, HIS and API with frequencies 69%, 68% and 56% respectively, with D′ = 0.97 for CAU (complete LD). The most common haplotype for AFA was Q ∼ EAV, at 48% and D′ = .99. Conclusions Low global LD was observed at the allele level for all populations. However, at the motif level haplotypes were in near complete LD suggesting that for the DPA1 ∼ DPB1 heterodimer the unit of selection for all populations is the combined amino acid motif rather than the allele, as previously observed in European Americans.