Molecular genotyping of fetal platelet antigens with uncultured amniocytes

OBJECTIVE: Amino acid substitutions in platelet membrane glycoproteins result in alloantigens implicated in neonatal alloimmune thromboctyopenia. We report the use of the reverse dot blot technique to genotype the five major fetal platelet alloantigens from amniotic fluid cells. STUDY DESIGN: We evaluated a patient with Bak^b platelet antibodies who had a previous pregnancy complicated by fetal intracranial hemorrhage. The father was heterozygous Bak^a/Bak^b, giving the pregnancy a 50% risk for platelet incompatibility between mother and fetus. Amniotic fluid was obtained at 16 weeks. Deoxyribonucleic 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. RESULTS: The reverse dot blot genotyping of uncultured amniocytes revealed the fetus to be Bak^a/Bak^a, thus not at risk for neonatal alloimmune thrombocytopenia. CONCLUSION: Precise knowledge of fetal platelet type of amniocentesis could obviate the need for fetal blood sampling and significantly alter prenatal management of neonatal alloimmune thrombocytopenia.