Frequency of HLA‐DRB1*15:03–DRB5 Haplotypes in Saudi Population: A Predominance of DRB5*01:01 and Rare Absence of DRB5

The strong linkage between HLA-DRB1*15:03 and DRB5*01:01 is well established globally, yet its expression patterns in Saudi donors remain underexplored. In this study, we analysed high-resolution HLA genotypes derived from next-generation sequencing of 28,927 stem cell donors of Saudi ethnicity registered in the Saudi Stem Cell Donor Registry. We identified carriers of DRB1*15:03 and recorded their DRB5 status. Descriptive statistics were used to summarise allele frequencies and haplotype configurations. We found DRB1*15:03 in 931 donors (3.22%). Of these, 926 individuals (99.46%) co-expressed DRB5*01:01, four (0.43%) carried DRB5*02:02 and one (0.11%) had no detectable DRB5 alleles. This study indicates a nearly universal linkage disequilibrium between DRB1*15:03 and DRB5*01:01 in the Saudi population, with the absence of DRB5 being infrequent. These findings confirm the infrequency of DRB5 absence and the importance of complete DRB3/4/5 typing to optimise donor matching and minimise immunogenic risk.