New mutations on platelet GPIIb in Sub-Saharan African populations revealed by genotyping discrepancies.

BACKGROUND

Previous studies of platelet allele frequencies in Sub-Saharan African populations enabled us to identify discrepancies in HPA-3 typing, suggesting the presence of new mutations and of a greater polymorphism than so far described in other populations.

OBJECTIVES

To analyze these discrepancies and to assess the factors leading to potential alloimmunization in these populations.

SAMPLES

Maternal samples from a Beninese woman following in utero death and panels of blood donors from Benin, Cameroon, Congo, and Pygmies from Central Africa.

TECHNIQUES

Genotyping was performed using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP), PCR-sequence specific primers (PCR-SSP) and sequencing techniques.

RESULTS

Three new mutations were found on GPIIb gene: exon 26 a) 2614C>A situated between HPA-3 and HPA-9w, b) 2645C>T downstream of HPA-3, c) intron 26 IVS26+89G>A. These mutations may lead to discrepant DNA typing results, due either to a localization in the complementary sequence recognized by the primer or to the appearance of a new enzyme restriction site. Furthermore, a bilateral linkage << deletion (Delta9 bp) intron 21 and the HPA-3b allele (exon 26) >> found in Caucasian, Asian, and Oceanian populations is not found in African populations, suggesting that its appearance was prior to HPA-3.

CONCLUSION

Three new mutations have been identified, two of them potentially immunogenic through their position. Furthermore, the polymorphism found on intron 26, localized in the complementary sequence of the PCR primer, may lead to a false typing assignation. It is therefore important to diversify techniques, both genomic (PCR-RFLP and PCR-SSP), and proteomic monoclonal antibody-specific immobilization of platelets antigen (MAIPA) to ensure accurate HPA antigenic system typing.