A 24-year-old woman presents with uterine bleeding at 10 weeks of gestation. Ultrasound shows a uterus larger than dates filled with a heterogeneous mass resembling a bunch of grapes. Suction curettage shows diffusely edematous villi with cisterns and circumferential trophoblastic proliferation, but no fetal parts. Immunohistochemistry for p57 shows absence of nuclear staining in cytotrophoblast and villous stromal cells. What is the genetic basis of this lesion?

• A Triploidy, 69XXY, with one maternal and two paternal haploid sets
• B Fertilization of an empty ovum by two sperm
• C Fertilization of an empty ovum by a single sperm followed by duplication of paternal genome ✓
• D Monosomy X with loss of the entire maternal genome

Explanation

Complete hydatidiform mole arises from fertilization of an empty ovum lacking maternal DNA. Most commonly a single sperm fertilizes the ovum and its haploid genome duplicates to give 46,XX entirely paternal in origin. Because all DNA is paternally imprinted, the maternally expressed p57 gene (CDKN1B) is silent, giving absent staining, which distinguishes it from partial mole and hydropic abortus where p57 is retained. Option A describes triploidy of a partial mole, which shows fetal tissue and retains p57.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.