The platelet alpha 2-integrin (GPIa) nucleotide-807 polymorphism is not associated with a risk for maternal-fetal human platelet antigen-5 incompatibility

Alloimmunization against human platelet antigen (HPA)-5 may lead to neonata l alloimmune thrombocytopenia. The HPA-5 dimorphism is expressed on the pla telet alpha 2 beta 1 integrin. The density of this receptor is associated w ith another dimorphism of the alpha 2 beta 1 integrin (nucleotide-807C/T). We hypothesized that anti-HPA-5b-induced neonatal thrombocytopenia is more likely to occur if the receptor is expressed at high than at low levels. Am ong 933 mother-child pairs, we identified 79 HPA-Saa mothers giving birth t o a HPA-5ab offspring. Seventeen mothers had HPA-Sb antibodies, but the off spring had a normal platelet count. We genotyped the offspring and mothers for the alpha 2-807C/T dimorphism to evaluate its relationship to antibody formation. There was no difference between the frequency of the 807C/T dimo rphism among children delivered from alloimmunized mothers and those from m others without antibodies (P>0.3). The frequency of the 807C/T dimorphism w as not different in the two maternal groups. In three maternal-fetal incomp atibilities, we observed at delivery normal platelet counts of platelets ty ped HPA-5b-alpha 2807T, despite increasing maternal antibody titers during the pregnancy. Our data do not support the hypothesis that the 8D7C/T dimor phism in the HPA-5ab children is a predisposing factor to either elicit all oimmunization against HPA-Sb or for neonatal alloimmune thrombocytopenia.