The first case of foetal neonatal alloimmune thrombocytopenia caused by anti‐HPA‐1a antibodies in Asian population

Abstract

Background and ObjectivesThe foetal neonatal platelet alloimmune thrombocytopenia (FNAIT) is one of the most frequent clinical implications of immunization against human platelet antigen (HPA). Maternal IgG platelet alloantibodies induce the destruction of foetal platelets leading to thrombocytopenia. In Caucasian, alloantibodies against HPA‐1a are responsible for the majority of severe FNAIT. As the frequency of HPA‐1bb homozygous individuals is very low in Asia, the clinical relevance of anti‐HPA‐1a alloantibodies is doubtful in this population.Study design and methodsRecently, we studied retrospectively sera from mothers with suspected FNAIT in Malaysia, a multi‐ethnic country. Surprisingly, we found in one maternal serum antibodies which may react with HPA‐1a. In this study, this FNAIT case, suspected to be caused by the anti‐HPA‐1a alloantibody, was investigated in more details.ResultsAntibody screening analysis using HPA‐phenotyped platelets by the antigen capture assay, MAIPA, showed specific reaction with the platelets GPIIb/IIIa carrying HPA‐1a antigenic determinants. In the control experiment, this antibody did not react with GPIIb/IIIa from HPA‐1bb individuals. In addition, no reaction was observed with other HPAs expressed on GPIIb/IIIa, GPIb/IX, GPIa/IIa, CD 109 and HLA Class I, both by screening tests and by cross‐match analysis (maternal serum against paternal platelets), in MAIPA. This result could be supported by the genotyping analysis of the family members (mother HPA‐1bb, father and the index child HPA‐1a positive).ConclusionsAlthough considered rare, this case shows for the first time the clinical relevance of anti‐HPA‐1a antibody in the pathogenesis of FNAIT among Asian population.