Abstract
Platelets play an integral part in the blood clotting process. The normal platelet count ranges from 150 to 400 x 103/μl. To date, twenty-four platelet-specific antigens have been defined. Human Platelet Antigens (HPA) 1-5 and –15 belong to diallelic systems and antibodies formed in response to immunization against these antigens, following transfusion or transplacental haemorrhage, have been responsible for life-threatening conditions in which the platelet counts of patients are markedly decreased. This is due to the destruction of platelets by platelet antigen - specific antibodies in Neonatal Alloimmune Thrombocytopenia and Post-Transfusion Purpura and in some instances, Platelet Refractoriness. In these clinical situations, transfusions of platelets from random donors do not result in post-transfusion platelet increments. Ideally, a database of blood donors who have been HPA typed should be established. This database can then be used to search for HPA – compatible donors and matched platelet donations can be made available to these patients.
The aims of this study were primarily to determine the HPA frequencies in the South African blood donor population and establish a register of HPA-typed donors. Secondly, the established frequencies would be compared to those of other world populations.
Anticoagulated blood samples from one hundred and fifty donors from each of the four main South African population groups were obtained for typing of HPA 1-5 and –15 by the PCR-SSP method in order to determine their gene and genotype frequencies and establish a platelet donor database.
Two methods of analyses were used to determine statistical similarities and differences between the South African population and a number of world populations (X2) and the degree of genetic distance between them (FST). Phylogenetic trees and Principal Components plots were constructed to illustrate relationships between populations.
The HPA gene and genotype frequencies of the South African blood donor population have been determined. An accurate, rapid method of HPA typing has been validated and effective HPA matched platelet transfusions are now possible for the first time in South Africa.
The gene frequencies of the White population have been found to be similar to those from European populations and the Bantu-speaking population frequencies compared favourably with those of other African populations.
The population group of mixed ethnicity (Coloured) was shown to have unique frequencies and were not similar to any of those populations chosen for comparison except with the other populations in South Africa.
Dr. R. L. Crookes
Prof. T.L. Coetzer
Prof. M. Dutton