Human platelet antigen polymorphisms (HPA-1, -2, -3, -4, -5 and -15) in major ethnic groups of Pakistan

Abstract

Gene frequencies of human platelet antigens (HPA) determine the magnitude of platelet immunological disorders like neonatal alloimmune thrombocytopenia, platelet refractoriness and ease of availability of particular HPA-typed platelet donors in a given community. However, the pattern of HPA in Pakistani population is not known. The aim of present study was to determine the gene frequencies of HPA (HPA-1 to -5 and -15) in individuals belonging to major ethnic groups and castes of Pakistani population. HPA genotyping was done in 593 individuals belonging to all ethnic groups of Pakistan, by polymerase chain reaction-sequence specific primers with detection on polyacrylamide electrophoresis. The gene frequencies of the 'a' and 'b' alleles of HPA-1 to -5 and -15 in Pakistanis were as follows: HPA-1a/b, 0.885/0.115; HPA-2a/b, 0.92/0.08; HPA-3a/b, 0.69/0.31; HPA-4a/b, 1/0; HPA-5a/b, 0.9/0.1; HPA-15a/b, 0.59/0.41. Except for significant difference regarding gene frequency of HPA-3 between Pathans and Sindhis, there was no significant difference of HPA-1 to -5 and -15 between major ethnic groups of Pakistan. The estimated mismatch probability regarding platelet antigens 1-5 and 15 in Pakistanis, after transfusion of random donor platelets, is from 14 to 37%. The expected incidence of neonatal alloimmune thrombocytopenia due to anti-HPA-1a in Pakistani pregnant females is < 1 of 1000 pregnancies and 8-12 of 1000 in case of anti-HPA-5b. Homozygosity of HPA-1b, -2b and -5b genotypes ranged from 1 to 2% in the Pakistani population, whereas homozygosity of HPA-3b and -15b was 11 and 18%. There is a need to establish donor registries typed for HPA in the transfusion centres of the country.