Neonatal alloimmune thrombocytopenia due to fetomaternal Zwb incompatibility

A case of neonatal alloimmune thrombocytopenia due to fetomaternal incompatibility against the platelet-specific antigen Zwb (PlA2) is described. The antibody was of the IgG class and did not fix complement in vitro. Its specificity was established by panel identification and by comparison to a Zwb antiserum. Gene dosage determinations of Zwa antigens on platelets of parents and child revealed that the mother was homozygous Zwa Zwa, while father and child were heterozygous for this antigen.