الفهرس 
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Abstract
Platelets are active cells, which assist in hemostasis and blood coagulation. Their glycocalyx contains glycoproteins(GP) molecules through which platelet bind to other cells to perform their functions. The GPs (GPIa, GPIb, GPIIb and GPIIIa,) are produced by substitutions of single amino acid. Human platelet antigens (HPAs) are polymorphic amino acid sequences found on these GPs
GPIIIa is considered the most polymorphic glycoprotein and bears HPA-1, HPA-4, and HPA-6. HPA-1 is defined as the most important antigenic system. HPA-1a or HPA-1b antigens are due to the existence of leucine or proline at position 33 of the GPIIIa where the “a” represents the common allele and the “b” represents the rare allele.
HPA are associated with alloimmunization as they are the targets for platelet antibodies that lead to platelet destruction in post-transfusion refractoriness (PTR) and purpura (PTP) after platelet transfusion. Patients who are treated for hematological diseases associated with thrombocytopenia are highly vulnerable to platelet refractoriness when treated by prophylactic concentrated platelet transfusions to prevent bleeding. Consequently, accurate donor compatibility for platelet transfusions is very essential.
The present study aimed to evaluate HPA-1 allele &genotype frequency among Egyptian donors & thrombocytopenic patients with hematological disorders.
HPA-1 genotyping was done by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique.
This study was carried out on 50 thrombocytopenic patients with hematological disorders with platelet count < 20,000 μL indicated for random donor platelet transfusion and 50 random Egyptian blood donors.
Cases and donors were subjected to history taking, clinical examination and routine laboratory investigations (CBC, Blood group phenotype,Virology: HBV, HCV, HIV). Detection of HPA-1 genotypes using PCR–restriction fragment length polymorphism (RFLP-PCR).
This study showed that no statistically significant difference between hematological patients and blood donors as regard HPA1 the genotype and allele frequency.
HPA 1a/1a genotype was found to be predominant among both haematological patients & blood donors (58% & 72% respectively) & the (a) allele is also the most common allele in both groups. Concerning alleles frequencies observed for the 100 cases in our study, the hematological patients allele frequencies were 0.77 and 0.23 of 1a and 1b respectively, and that of blood donors 1a and 1b were: 0.84 and b: 0.16, respectively. This reveals that the (b) allele is less frequent than the (a) allele and that degree of HPA-1 system polymorphism is considered high.
In the current study, In case of platelet transfusion the mismatch probability between the subjects of the present study was calculated using the blood donors HPA genotype frequency. The probability of incompatibility of HPA-1 showed that homozygous for the (b) allele hematological patients more alloimmunised as the probability of incompatible is nearly 100% due to the high genotype frequency of (aa) and (ab) in blood donors.