Immunogenetic polymorphism of human platelet antigens in the Saudi population: Insights into genetic diversity and alloimmune risk.

Background and objectives: Population study on immunogenetic polymorphism of human platelet antigens (HPAs) may aid in predicting the risk of alloimmune thrombocytopaenia syndromes. We aimed to characterize the diversity of HPAs in Saudis and estimate the alloimmunization risk.

Materials and methods: We assessed the genotype and allele frequencies of HPA-1 to -11 and HPA-15 in 118 Saudi blood donors using a real-time polymerase chain reaction assay. We estimated the mismatch risk associated with blood transfusions and pregnancies for each individual allele. Furthermore, we evaluated the mismatch risk for various haplotypes constructed from all HPA genes, as well as focusing on the highly immunogenic HPA-1 and -5 systems. Moreover, our data were integrated with data from other populations to perform principal component analysis (PCA) and phylogenetic analyses.

Results: The frequencies of the 'a' and 'b' alleles for the polymorphic HPA-1, -2, -3, -5 and -15 genes were as follows: HPA-1a/b: 0.831/0.169; HPA-2a/b: 0.856/0.144; HPA-3a/b: 0.729/0.271; HPA-5a/b: 0.822/0.178 and HPA-15a/b: 0.449/0.561. A slight polymorphism was observed in HPA-9: 0.992/0.008. The HPA-4, -6, -7, 8, -10 and -11 genes were found monomorphic. We found 54 different concatenated haplotypes; the mismatch probability of each varied between 0.85% and 11.72%. The PCA indicated a significant non-random grouping of populations into four genetically distinct clusters. This pattern is confirmed by the neighbour-joining phylogenetic tree.

Conclusion: This study is useful for HPA immunogenetics and offers a database for further research on transfusion medicine, alloimmune thrombocytopaenia as well as on population genetics in the Arabian Peninsula and beyond.