Triple genetic identities for the complete hydatidiform mole, placenta and co-existing fetus after transfer of a single in vitro fertilized oocyte: Case report and possible mechanisms

We found different genotypes for the complete hydatidiform mole (CHM), placenta and co-existing fetus derived from a single in vitro fertilized human oocyte by the analysis of short tandem repeat (STR) DNA markers. The molar tissue was found to be heterozygously androgenetic. The fetus and placenta contained identical maternal, but different paternal genomes. Two models were proposed to account for the identification of triple genetic identities in a single fertilized oocyte. In the first model, the oocyte was fertilized by a diploid sperm, resulting in diandric triploidy. Premature cytokinesis resulted in early splitting of a cytoplasmic fragment with one copy of the replicated sperm chromosome, which developed into a heterozygous CHM. The bipolar spindle in syngamy pulled the other copy of sperm chromosomes and replicated oocyte chromosomes to form two blastomeres, which develop into the fetus and placenta, respectively. In the second model, the oocyte was fertilized by two haploid sperms, followed by tripolar spindle formation. Whatever is the mechanism, this case provides direct evidence that CHM can be derived from an oocyte containing an intact maternal genome.