Molecular genetic testing from paraffin-embedded tissue distinguishes nonmolar hydropic abortion from hydatidiform mole

Background: Diagnosis of hydatidiform mole by histology and ploidy analysis is limited by overlap of criteria for nonmolar hydropic abortion, complete mole, and partial mole. With early presentation, diagnosis is difficult du e to limited tissue and lack of clinical features. Accurate diagnosis of th ese entities is important for both prognosis and patient management. We ass essed a polymerase chain reaction (PCR) assay for polymorphic short tandem repeats (STR) for discrimination between nonmolar hydropic abortion, comple te mole, and partial mole based on the genetic composition of molar pregnan cies, Methods: Seventeen cases of products of conception (POC) diagnosed by histo logy and flow cytometry ploidy analysis were studied retrospectively. PCR w as performed using maternal and chorionic villus DNA extracted from microdi ssected, formalin-fixed, paraffin-embedded tissue sections. Allelic pattern s for up to eight well-characterized polymorphic STR loci were determined u sing the GenePrint Fluorescent STR System (Promega Corporation, Madison, WI ). The presence of three villus alleles at a single locus was interpreted a s partial mole. Detection of only one allele in the villi, different from a ll maternal allele(s) at the same locus, was interpreted as a complete mole . Results: This technique identified eight complete moles previously diagnose d as complete mole (3), hydatidiform mole, otherwise unspecified (1), hydro pic villi (2), hydropic villi versus partial mole (1), and partial mole (1) . The diagnoses of five partial moles by the molecular assay were consisten t with the diagnoses by histology and flow cytometry. One nonmolar gestatio n was identified, which had been diagnosed previously as hydropic villi. In three cases, maternal DNA amplification was insufficient for definitive di agnosis. Conclusion: Molecular genetic testing of POC from paraffin-embedded tissue accurately distinguishes complete mole, partial mole, and nonmolar hydropic abortion. Identification of triploidy by flow cytometry can confirm a hist ological impression of partial mole. Histological and ploidy analysis of PO C results in underdiagnosis of complete moles.