Genetic studies on hydatidiform moles.

Using an historical approach, this article describes how genetic studies have elucidated the two entities into which the syndrome of hydatidiform mole can now be divided. Partial moles are triploid, have a maternal chromosomal set, and are associated with the presence of a fetus. Complete moles lack a fetus and are always diploid and androgenetic in origin, having two sets of paternal chromosomes. They are most often XX and homozygous, the most likely origin being by duplication of a haploid sperm. About 4% of complete moles have been shown to by XY and heterozygous, the most likely origin being by dispermy. The frequency of partial and complete mole observed depends on the method of ascertainment. Among spontaneous abortions, partial moles are more common than complete moles, but among cases having an elective termination of pregnancy because of a prior diagnosis of hydatidiform mole, complete mole is the more common. Patients with either type of mole may require treatment for persistent trophoblastic activity. More prospective studies of cases in which the type of mole has been confirmed by genetic studies are required in order to find out whether (a) patients with complete moles are more likely than those with partial moles to require treatment for persistence of trophoblastic activity after evacuation; and (b) heterozygous complete moles have a different prognosis from the point of view of malignant sequelae than homozygous complete moles.