MOLECULAR GENOTYPING OF FETAL PLATELET ANTIGENS WITH UNCULTURED AMNIOCYTES

OBJECTIVE: Amino acid substitutions in platelet membrane glycoproteins result in alloantigens implicated in neonatal alloimmune thromboctyop enia. 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 w ho had a previous pregnancy complicated by fetal intracranial hemorrha ge. The father was heterozygous Bak(a)/Bak(b), giving the pregnancy a 50% risk for platelet incompatibility between mother and fetus. Amniot ic fluid was obtained at 16 weeks. Deoxyribonucleic acid was extracted from uncultured amniocytes and amplified with polymerase chain reacti on. These products were hybridized to filters containing oligonucleoti des specific for each of the 10 different platelet antigen alleles. Re activity was detected with a chromogenic substrate. RESULTS: The rever se dot blot genotyping of uncultured amniocytes revealed the fetus to be Bak(a)/Bak(a), thus not at risk for neonatal alloimmune thrombocyto penia. CONCLUSION: Precise knowledge of fetal platelet type by amnioce ntesis could obviate the need for fetal blood sampling and significant ly alter prenatal management of neonatal alloimmune thrombocytopenia.