Regarding the cytogenetics of a classic complete hydatidiform mole, which statement is correct?

• A Triploid, with one maternal and two paternal haploid genomes
• B Tetraploid, arising from fertilisation of a normal ovum by two sperm
• C Diploid 46,XY with equal maternal and paternal contribution
• D Diploid 46,XX in about 90 percent of cases, with all nuclear genetic material paternally derived ✓

Explanation

About 90 percent of complete moles are 46,XX, formed when an empty (anucleate) ovum is fertilised by a 23,X sperm that then duplicates its genome, so all chromosomes including sex chromatin are paternal; the remaining 10 percent are 46,XY from dispermy, still entirely paternal. Mitochondrial DNA remains maternal. Triploidy with one maternal and two paternal sets defines a partial mole, and tetraploidy is not a recognised molar mechanism, which eliminates options A and B.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.