Neonatal alloimmune thrombocytopenic purpura induced by anti-Bak(a): a case report and review of the literature.

We report a case of neonatal alloimmune thrombocytopenic purpura after an uneventful pregnancy. The baby had systemic purpura at birth and his platelet count was 6 X 10(9)/1. He was treated with maternal platelets and one week later his platelets were normalized. It was the second pregnancy of the mother; she received a blood transfusion after the delivery of her first child. The mother was HLA DR3 positive, an antigen frequently implicated in neonatal alloimmune thrombocytopenic purpura. The antibody reacted with both P1A1 positive and negative platelets which excluded anti-P1A1 type, the antibody most involved in neonatal alloimmune thrombocytopenia. This antibody reacted with platelets of 46 out of 53 random donors (87%); this approached the 90.8% frequency of Bak(a) reported in the Netherlands. Later this antibody was typed as anti-Bak(a). A discussion and a review of the literature is given.