85-P

Abstract

Aim The HLA haplotype frequencies for Middle Eastern populations are not well known relative to the rest of the world. At The King Faisal Specialist Hospital and Research Center in Riyadh we have collected HLA typing information for thousands of donors and cord blood units from years of stem-cell and renal transplants with the goal of establishing a stem cell registry in the Kingdom of Saudi Arabia. We aim in this study to use these HLA typings to estimate Saudi population haplotype frequencies and in follow-on work to project HLA match rates for the Saudi population as the registry expands. Methods We calculated HLA A∼C∼B∼DRB1∼DQB1 haplotype frequencies from 2,723 Saudi donors and cord blood units typed by DNA methods, resolving phase and allelic ambiguity using the Expectation Maximization algorithm. Haplotype frequencies were estimated to the allele family level for class I loci and to high resolution at class II loci. Results The most common Saudi HLA haplotype was A∗02∼C∗06∼B∗50∼DRB1∗07:01∼DQB1∗02:02 at a frequency of 4.5%. This haplotype is also the 32nd most common haplotype in the US Caucasian population at a frequency of 0.38%. The 2nd most common Saudi haplotype was A∗02∼C∗07∼B∗07∼DRB1∗15:01∼DQB1∗06:02 at 1.7% frequency, which is also the 4th most common haplotype among US Caucasians, and within Europe is most common in Scandinavia. The 3rd most common Saudi haplotype, A∗26∼C∗07∼B∗08∼DRB1∗03:01∼DQB1∗02:01 at 1.6% frequency, is the 14th most common haplotype in US Asian Pacific Islanders at 0.64%, but is quite rare in US Caucasians (rank 466; 0.0036%). Conclusions his pilot haplotype frequency study and the match rate projection to follow will help to form a data-driven approach to the establishment of a robust stem cell registry of adult donors and cord blood units that will aid the Saudi population in need of transplant. Collection of more detailed ancestry information on Saudi donors has the potential to improve match estimates and ensure all subpopulations are well-served.