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.