FREQUENCY AND FUNCTIONAL RELEVANCE OF GENETIC THREONINE(145) METHIONINE(145) DIMORPHISM IN PLATELET GLYCOPROTEIN IBA IN AN ITALIAN POPULATION/

Background: Threonine(145)/methionine(145) dimorphism in platelet glyc oprotein (GP) Ib alpha defines the human platelet antigen (HPA)-2 syst em that has been implicated in refractoriness to HLA-matched platelet transfusion and in neonatal immune thrombocytopenic purpura. Study Des ign and Methods: The occurrence of this amino acid dimorphism was inve stigated in 379 Italian blood donors by studying their genomic DNA. Tw o oligonucleotide primers, Ib alpha-3 (5'GGACGTCTCCTTCAACCGGC-3') and Ib alpha-4 (5'-GCTTTGGTGGGGAACTTGAC-3'), were used in a polymerase cha in reaction to generate a 591-base pair fragment that was digested wit h the restriction enzyme Acy I. To investigate whether this dimorphism is involved in the binding of von Willebrand factor (vWF) to GPIb, th e binding of vWF to the GPIb/IX complex was measured in two Met(145)/M et(145) and two Thr(145)/Thr(145) subjects. Results: The genotypic fre quencies are 78.9% for Thr/Thr, 19.8% for Thr/Met), and 1.3% for Met/M et; the allelic frequencies are 88.8% for Thr(145) and 11.2% for Met(1 45). Estimates for binding of subunit molecules per platelet at satura tion and inhibition constant in mol per L, respectively, follow. In th e presence of ristocetin (0.5 mg/mL), they are 11,460+/-2,040 and 1.26 +/-0.44 x 10(-8) for normals and 11,230+/-2,330 and 1.29+/-0.48 x 10(- 8) for patients. In the presence of botrocetin (2.5 mu g/mL), they are 64,260+/-7,760 and 2.99+/-0.96 x 10(-8) for normals and 65,770+/-11,5 70 and 2.47+/-0.22 x 10(-8) for patients. Platelet aggregation respons es obtained using platelet-rich plasma from donors with Met(145)/Met(1 45) or Thr(145)/Thr(145) genotype were within normal limits. Conclusio n: Genotypic and phenotypic frequencies in the HPA-2 system in this po pulation are consistent with those reported among the white population . Furthermore, the HPA-2 system is not involved in the binding of vWF to GPIb.