A partial hydatidiform mole with 2N/3N mosaicism identified by molecular analysis

Purpose: A placenta with a partial hydatidiform mole was studied using DNA polymorphic markers to determine whether it has a triploid cell line. Method: Parent-mole transmission. of alleles at 23 polymorphic loci was traced in cells from a molar region and a normal-looking region of the placenta by polymerase chain reaction (PCR) amplification or Southern blot analysis, both followed by densitometric analysis. Results: Allele patterns for 8 of the 23 loci were identical between the DNA from the molar and normal regions of the placenta, while those of the remaining 15 loci were uninformative. In the molar region, the band intensity for the paternally derived allele at each informative locus was always greater than that of the maternally derived allele, the average intensity ratio of the former to the latter being 1.5, whereas the ratio in the normal region was even. Conclusions: The results suggested that the molar region was a mixoploid consisting of diploid and triploid cells and the phenotypically normal region had a mainly diploid constitution. It is most likely that the placenta may have originated from a single diploid or triploid conceptus, followed by postzygotic gain or loss of a paternal haploid set, and that an extra paternal set contributed to hydropic changes of the placenta.