Genetic studies on hydatidiform moles. II. The origin of complete moles.

An investigation of 50 histologically complete hydatidiform moles was made by examining the molar tissue after termination of pregnancy. Attempts were made to study chromosomes and 11 polymorphic enzymes in the moles and in the blood of the patient and her spouse, although not all studies were possible on every case. Useful information about the origin of the mole was obtained in 28 cases. In no case was there evidence of a maternal contribution and in 14 cases a maternal contribution was definitely excluded. In 27 cases, including the 5 tested who have subsequently required treatment, the mole was homozygous for all genetic markers examined. There were 32 examples, arising in 21 moles, of loci homozygous in the mole where the male parent was known to be heterozygous. There was a single example of a mole heterozygous at one proximal locus (PGM3). The findings are in favour of the doubling of a haploid genome as the most likely origin of the vast majority of complete moles.