[1061] In Situ Genetic Analysis of Hydatidiform Moles by Polymorphic Deletion Probe Fluorescence In Situ Hybridization

S Chiang, L Fazlollahi, A Nguyen, DJ Roberts, AJ Iafrate. Massachusetts General Hospital, Boston

Background: Molecular genotyping can aid in the diagnosis of complete (CHM) and partial hydatidiform moles (PHM) and nonmolar abortions (NMA). Polymorphic deletion probes (PDP), recently developed FISH probes based on copy number variants, are highly polymorphic and can genetically distinguish between cells from any 2 individuals in situ. Since products of conception (POC) contain maternal and villous tissue, the genotypes of mother and zygote based on deleted or expressed alleles can be assessed. We used a panel of 3 informative PDP (one probe each from chromosomes 2p, 4q and 8p) to determine the genetic identity of molar and nonmolar POC in situ with a focus on whether villous tissue lacked maternal contribution (indicating CHM) and on diploidy vs. triploidy (indicating PHM).
Design: FISH analysis using 3 PDP was performed on 40 archival POC, including 13 CHM, 13 PHM, 13 NMA, and 1 placental mesenchymal dysplasia (PMD), with supporting ancillary studies (p57 immunostaining, flow cytometry, cytogenetics). The following genotype pairs were considered informative for a definitive diagnosis of CHM: +/+ decidua and -/- villi; -/- decidua and +/+ villi. Combined 8p PDP-FISH and p57 immunofluorescence (IF) was performed on PMD.
Results: 3 probe PDP-FISH analysis was successful in all cases studied, with genotypes clearly identified for maternal and villous tissue. PDP-FISH permitted a definitive diagnosis of CHM in 5/13 known cases for which genotypes of maternal and villous tissue were mutually exclusive (Fig. 1). 13 CHM were diploid and homozygous for all PDP, consistent with monospermy. Based on a low rate of homozygosity for all probes in NMA (1/13), we calculated a 92.3% probability that any case is a CHM if all probes are homozygous. Triploidy was shown in 13 PHM, including 6 cases in which PDP-FISH allowed definitive determination of diandric triploidy. In PMD, FISH-IF showed p57 expression in heterozygous (+/-) cytotrophoblasts and syncitiotrophoblasts and no expression in homozygous villous stromal cells, confirming mosaicism in situ.
Conclusions: PDP-FISH analysis can be used in clinical practice and research studies to subtype hydatidiform moles and evaluate nonmolar POC with genetic abnormalities.

Category: Gynecologic & Obstetrics

Tuesday, March 23, 2010 1:00 PM

Poster Session IV # 131, Tuesday Afternoon


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