Frequency distribution of antigens in the human platelet antigen-1 system in the western Indian population.

Abstract

Neonatal alloimmune thrombocytopenic purpura (NAITP) occurring because of fetomaternal incompatibility in the human platelet antigen-1 (HPA-1) system is increasingly being detected worldwide. Several studies have reported the frequency and distribution of HPA-1 alleles in different countries and ethnic populations. A paucity of data regarding the frequency of the antigens in the HPA-1 system in the Indian population prompted an undertaking of this study. The molecular method of genotyping the platelet antigens is preferred to serology. It will enable future prenatal diagnosis in mothers suspected to have NAITP so that they can be managed better. Five hundred six unrelated subjects were screened for the alleles in the HPA-1 system, of which 185 were healthy males and 321 were females. DNA was extracted from the peripheral blood WBCs of these subjects, followed by PCR amplification and agarose gel electrophoresis of the PCR-amplified products. Four hundred two out of 506 subjects (79.44%) were found to be homozygous for HPA-1a. Ninety-nine subjects (19.57%) were heterozygous HPA-1a/HPA-1b, and five subjects out of 506 (0.99%) were homozygous for HPA-1b. Homozygosity for HPA-1b exists in the Indian population at a frequency of 0.99 percent, whereas homozygosity for HPA-1a is present in approximately 79 percent of the population. Hence, 0.98 x 0.79 of the females (0.77%) in the reproductive age group are likely to be pregnant with an HPA-1a-positive fetus, leading to a setting in which NAITP might develop. The development of NAITP also depends on the HLA type of the mother; nevertheless, the number of pregnancies in which the fetus is at risk for NAITP in India is quite significant.