Molecular genotyping of fetal platelet antigens with uncultured amniocytes.

Abstract

Amino acid substitutions in platelet membrane glycoproteins result in alloantigens implicated in neonatal alloimmune thrombocytopenia. We report the use of the reverse dot blot technique to genotype the five major fetal platelet alloantigens from amniotic fluid cells. We evaluated a patient with Bakb platelet antibodies who had a previous pregnancy complicated by fetal intracranial hemorrhage. The father was heterozygous Baka/Bakb, giving the pregnancy a 50% risk for platelet incompatibility between mother and fetus. Amniotic fluid was obtained at 16 weeks. Deoxyribonuleic acid was extracted from uncultured amniocytes and amplified with polymerase chain reaction. These products were hybridized to filters containing oligonucleotides specific for each of the 10 different platelet antigen alleles. Reactivity was detected with a chromogenic substrate. The reverse dot blot genotyping of uncultured amniocytes revealed the fetus to be Baka/Baka, thus not at risk for neonatal alloimmune thrombocytopenia. Precise knowledge of fetal platelet type by amniocentesis could obviate the need for fetal blood sampling and significantly alter prenatal management of neonatal alloimmune thrombocytopenia.