Parental origin and phenotype of triploidy in spontaneous abortions: Predominance of diandry and association with the partial hydatidiform mole

The origin of human triploidy is controversial. Early cytogenetic studies f ound the majority of cases to be paternal in origin; however, recent molecu lar analyses have challenged these findings, suggesting that digynic triplo idy is the most common source of triploidy. To resolve this dispute, we exa mined 91 cases of human triploid spontaneous abortions to (1) determine the mechanism of origin of the additional haploid set, and (2) assess the effe ct of origin on the phenotype of the conceptus. Our results indicate that t he majority of cases were diandric in origin because of dispermy, whereas t he maternally-derived cases mainly originated through errors in meiosis II. Furthermore, our results indicate a complex relationship between phenotype and parental origin: paternally-derived cases predominate among "typical" spontaneous abortions, whereas maternally-derived cases are associated with either early embryonic demise or with relatively late demise involving a w ell-formed fetus. As the cytogenetic studies relied on analyses of the form er type of material and the molecular studies on the latter sources, the di screpancies between the data sets are explained by differences in ascertain ment. In studies correlating the origin of the extra haploid set with histo logical phenotype, we observed an association between paternal-but not mate rnal-triploidy and the development of partial hydatidiform moles. However, only a proportion of paternally derived cases developed a partial molar phe notype, indicating that the mere presence of two paternal genomes is not su fficient for molar development.