Platelet antigen HPA-5b (Bra) in an Algerian population

Allelic polymorphisms of human platelets-specific alloantigens in South Tunisian population

OBJECTIVES

Human platelet-specific alloantigens (HPA) are polymorphic epitopes which vary among ethnic groups.

BACKGROUND

In Tunisia, HPA frequencies were determined in North and centre; however, the pattern of HPA in South Tunisian population is not been studied yet. The aim of this work was to determine allelic frequencies of HPA-1, -3, and -5 systems in south Tunisian population, in order to estimate the risk of anti-platelet allo-immunization and to create a register of HPA-typed blood donors.

METHODS

Our study concerned 212 unrelated healthy, regular blood donors from southern Tunisia. Allelic polymorphisms of each system were determined using a polymerase chain reaction with sequence-specific primers.

RESULTS

Genotype frequencies a/a, a/b, and b/b were, respectively, 0.670, 0.288, and 0.042 for HPA-1 system, 0.430, 0.462, and 0.108 for HPA-3 system, and 0.750, 0.241, and 0.009 for HPA-5 system. The allele frequencies were 0.814 and 0.186 for HPA-1a and -1b alleles; 0.660 and 0.340 for HPA-3a and -3b alleles and 0.870, and 0.130 for HPA-5a and -5b alleles.

DISCUSSION

The reported frequencies are more similar to those of Caucasians than those of north Tunisian population.

Platelet-specific alloantigens and antibodies in Tunisian women after three or more pregnancies

Pregnancy may allow alloimmunization against human platelet antigens (HPA), which can lead to neonatal alloimmune thrombocytopenia (NAIT). The specificities of alloantibodies are closely related to the distribution of the HPA systems. A total of 281 Tunisian multiparous women (mean number of pregnancies: 4.5) were phenotyped for the HPA-1, -3 and -5 systems, by monoclonal antibody immobilization of platelet antigens (MAIPA). We searched for antibodies against HPA-1a, HPA-3a, HPA-5b and HPA-5a in HPA-1b1b, HPA-3b3b, HPA-5a5a and HPA-5b5b individuals, respectively. The gene frequencies were: 0.83 for HPA-1a, 0.17 for HPA-1b, 0.78 for HPA-3a, 0.22 for HPA-3b, 0.82 for HPA-5a and 0.18 for HPA-5b. Anti-HPA-5b antibodies were present in eight sera and anti-HPA-3a antibodies were present in one serum. The anti-HPA-5b system is the most frequently involved in platelet alloimmunization in Tunisian multiparous women. However, prospective trials are required to confirm this result and to determine the exact frequencies and clinical relevance of platelet alloantibodies in pregnant Tunisian women.

Gene frequencies of human platelet antigens 1-5 in indigenous Australians in Western Australia

The frequencies of human platelet antigen (HPA) systems vary between different racial groups; however, HPA frequency data for some racial groups are still incomplete. We report the distribution of HPA 1-5 systems in Australian Aborigines from a remote community in the north-west of Australia and compare our findings with HPA observed in a Western Australian blood donor population. Using a polymerase chain reaction (PCR) with sequence-specific primers, 185 indigenous Australians and 1000 Western Australian blood donors were genotyped for each of the HPA 1-5 systems. Comparison of gene frequencies of alleles from HPA-1, -2, -3 and -5 systems showed significant differences between Aboriginal people and Western Australian blood donors (P < 0.001). In particular, the frequency of HPA-3b (0.068) in the Australian Aboriginals, from this study, was one of the lowest reported, whilst the frequency of HPA-5b (0.246) was one of the highest for this allele. Gene frequencies were similar to those reported for central Australian Aborigines but with no other ethnic group. In conclusion, this study confirms significant differences in HPA distributions between indigenous Australians, Australian blood donors and other racial groups. These results indicate a higher potential risk of alloimmunization to HPA-1, -2 and -3 in Australian Aborigines receiving transfusion therapy from a Caucasian blood donor population, thereby having practical implications for transfusion and pregnancy risks in people of Aboriginal origin.

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

BACKGROUND

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.

STUDY DESIGN AND METHODS

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.

RESULTS

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.

CONCLUSION

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.

Frequencies of platelet-specific alloantigen systems 1-5 in three distinct ethnic groups in Brazil

The human platelet antigen (HPA) systems are related to immune platelet disorders as well as to the development of occlusive vascular disease. Several distinct biallelic HPA systems are known, and a heterogeneous distribution of HPA alleles has been described among distinct ethnic groups. In this study we genotyped 320 carefully selected individuals from three distinct ethnic groups in Brazil (Caucasians, Blacks and Amazonian Indians) for the HPA-1, -2, -3, -4 and -5 systems. A similar prevalence for all HPA alleles was found in Brazilians of Caucasian and Black descent. These data contrast with those reported for similar ethnic groups in other countries. Among the Amazonian Indians, no b allele of the HPA-1, -4 and -5 systems was identified. The data presented here could be useful in the diagnosis of alloimmune platelet disease, in genetic counselling and in the development of screening programmes for HPA-related diseases.

Gene frequencies of human platelet antigens in the Tunisian population

Gene frequencies for the human platelet antigens HPA-1, -3 and -5 in the Tunisian population were determined by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) on 93 volunteer blood donors (78 were tested for HPA-1, 90 for HPA-3 and 93 for HPA-5). This study shows the highest frequencies of the HPA-1b (0.25) and HPA-5b (0.22) yet recorded. These antigens are considered as markers of a high risk of platelet alloimmunisation in other populations, and for this reason particular attention should be paid in the case of pregnancy or blood transfusion in this population. The 9 base pair deletion located in intron 21 of the GPIIb gene associated with HPA-3b determinant is present in this population. No individual showed the polymorphism associated with HPA-1b (T-->G at codon 40 of the GPIIIa).

Platelet alloantigens HPA-1, -2, -3, -5 and -6b in Finns

The human platelet alloantigens HPA-1, -2, -3, -5 and -6b in the Finnish population were determined using allele specific restriction analysis (PCR-ASRA) for HPA-1, -2, -3 and -5 and monoclonal antibody immobilized platelet antigen (MAIPA) assay for HPA-1, -3a, -5b and -6b. No discrepancies were observed between the results obtained with the PCR-method and those obtained serologically. The gene frequencies obtained from 200 unrelated Finns were 0.86 and 0.14 for HPA-1a and -1b, 0.91 and 0.09 for HPA-2a and -2b, 0.59 and 0.41 for HPA-3a and -3b and 0.95 and 0.05 for HPA-5a and -5b. The frequency of the HPA-5b allele (10%) is lower in Finns than in Central- or South-European populations (20-30%). The HPA-1, -2 and -3 frequencies did not deviate from those observed in other European populations. The rare HPA-6b antigen was observed in three of 127 individuals from south-eastern Finland (2.4%), which suggests that the frequency of this allele in Finland is higher than previously thought.