The propensity to malignancy of dispermic heterozygous moles

Complete hydatidiform moles may originate from either the fertilization of an empty egg by a haploid sperm followed by duplication (producing a monospermic, homozygous mole) or the fertilization of such an egg by two haploid sperms (producing a dispermic, heterozygous mole). This difference in the mechanism leading to the formation of complete moles raises the question of whether the risk of subsequent malignancy is influenced by the zygosity of the mole. We have compared the incidence of postmolar sequelae in patients with homozygous and heterozygous moles. Using chromosomal heteromorphisms, human lymphocyte antigen (HLA) and phosphoglucuromutase 1 (PGM1) polymorphisms, we established the androgenetic origin of complete mole in 84 of 91 cases. Homozygosity was confirmed in 51 moles, and we found ten heterozygous moles. Five of ten patients with heterozygous moles developed postmolar trophoblastic disease, whereas only two of the 51 patients with homozygous moles had postmolar trophoblastic disease (an additional five patients showed signs of degenerating residual trophoblasts). The XY sex chromosome constitution of the two in vitro choriocarcinoma cell lines examined here provides further evidence of the propensity to malignancy of heterozygous moles.