Flow cytometric and clinicopathologic study of 197 hydatidiform moles with special reference to the significance of cytometric aneuploidy and literature review

Genetics, not the uterine environment, drive the formation of trophoblast inclusions: Insights from a twin study

INTRODUCTION

Trophoblast inclusions (TIs) are associated with aneuploidy and pregnancy loss and have thus been considered to be a marker of genetic abnormality. However, to date, no study has specifically explored whether TIs are a manifestation of fetal genetics or, rather, the result of the intrauterine environment. The goal of this study was to compare the frequency of TIs in the placentas of monozygotic (MZ) and dizygotic (DZ) twin pairs in order to determine whether the formation of TIs is genetically driven or not.

METHODS

We performed a retrospective case series of placentas from 48 twin pairs. The placentas were grouped based on zygosity: MZ, DZ, or unknown (UZ). The average number of total TIs per slide was calculated for each twin individual and the mean absolute difference in the total TIs per slide between the twin pairs was calculated for each zygosity group and compared.

RESULTS

The mean difference in the total TIs per slide for DZ twins was significantly greater than the mean difference in the total TIs per slide for MZ twins (p = 0.003). The mean difference in the total TIs per slide for the UZ group was also significantly greater than the mean difference in total TIs per slide between MZ twin pairs (p = 0.028).

DISCUSSION

Our finding that MZ twins were significantly more concordant than DZ twins for the average number of TIs per slide supports the conclusion that TIs are intrinsic to the genetics of the fetus, not the uterine environment.

Diagnostic reproducibility of hydatidiform moles: ancillary techniques (p57 immunohistochemistry and molecular genotyping) improve morphologic diagnosis for both recently trained and experienced gynecologic pathologists

Distinction of hydatidiform moles from nonmolar specimens (NMs) and subclassification of hydatidiform moles as complete hydatidiform mole (CHM) and partial hydatidiform mole (PHM) are important for clinical practice and investigational studies; however, diagnosis based solely on morphology is affected by interobserver variability. Molecular genotyping can distinguish these entities by discerning androgenetic diploidy, diandric triploidy, and biparental diploidy to diagnose CHMs, PHMs, and NMs, respectively. Eighty genotyped cases (27 CHMs, 27 PHMs, 26 NMs) were selected from a series of 200 potentially molar specimens previously diagnosed using p57 immunohistochemistry and genotyping. Cases were classified by 6 pathologists (3 faculty level gynecologic pathologists and 3 fellows) on the basis of morphology, masked to p57 immunostaining and genotyping results, into 1 of 3 categories (CHM, PHM, or NM) during 2 diagnostic rounds; a third round incorporating p57 immunostaining results was also conducted. Consensus diagnoses (those rendered by 2 of 3 pathologists in each group) were also determined. Performance of experienced gynecologic pathologists versus fellow pathologists was compared, using genotyping results as the gold standard. Correct classification of CHMs ranged from 59% to 100%; there were no statistically significant differences in performance of faculty versus fellows in any round (P-values of 0.13, 0.67, and 0.54 for rounds 1 to 3, respectively). Correct classification of PHMs ranged from 26% to 93%, with statistically significantly better performance of faculty versus fellows in each round (P-values of 0.04, <0.01, and <0.01 for rounds 1 to 3, respectively). Correct classification of NMs ranged from 31% to 92%, with statistically significantly better performance of faculty only in round 2 (P-values of 1.0, <0.01, and 0.61 for rounds 1 to 3, respectively). Correct classification of all cases combined ranged from 51% to 75% by morphology and 70% to 80% with p57, with statistically significantly better performance of faculty only in round 2 (P-values of 0.69, <0.01, and 0.15 for rounds 1 to 3, respectively). p57 immunostaining significantly improved recognition of CHMs (P<0.01) and had high reproducibility (κ=0.93 to 0.96) but had no impact on distinction of PHMs and NMs. Genotyping provides a definitive diagnosis for the ∼25% to 50% of cases that are misclassified by morphology, especially those that are also unresolved by p57 immunostaining.

Report of four new patients with protein-truncating mutations in C6orf221/KHDC3L and colocalization with NLRP7

To date, two maternal-effect genes have been shown to have causative roles in recurrent hydatidiform moles (RHMs); NLRP7 that is mutated in 48-60% of patients with RHMs and C6orf221 (HUGO-approved nomenclature is now KHDC3L), a recently identified gene, that is mutated in 14% of patients with RHMs who are negative for NLRP7 mutations. We sequenced KHDC3L in 97 patients with RHMs and reproductive loss who are mostly negative for NLRP7 mutations. We identified three unrelated patients, each homozygous for one of the two protein-truncating mutations, a novel 4-bp deletion resulting in a frameshift, c.299_302delTCAA, p.Ile100Argfs*2, and a previously described 4-bp deletion, c.322_325delGACT, p.Asp108Ilefs*30, transmitted on a shared haplotype to three patients from different populations. We show that five HM tissues from one of these patients are diploid and biparental similar to HMs from patients with two defective NLRP7 mutations. Using immunofluorescence, we show that KHDC3L protein displays a juxta perinuclear signal and colocalizes with NLRP7 in lymphoblastoid cell lines from normal subjects. Using cell lines from patients, we demonstrate that the KHDC3L mutations do not change the subcellular localization of the protein in hematopoietic cells. Our data highlight the similarities between the two causative genes for RHMs, KHDC3L and NLRP7, in their subcellular localization, the parental contribution to the HM tissues caused by them, and the presence of several founder mutations and variants in both of them indicating positive selection and adaptation.

NLRP7 mutations in women with diploid androgenetic and triploid moles: a proposed mechanism for mole formation

Hydatidiform mole is an aberrant pregnancy with abnormal embryonic development and hydropic placental villi. Common moles are sporadic, not recurrent and affect one in every 1500 pregnancies in Western societies. Approximately, half of common moles are complete and mostly diploid androgenetic, whereas the remaining are partial and mostly triploid diandric. NLRP7 has been found to be responsible for a recurrent form of molar pregnancies. Recently, we showed that patients with NLRP7 mutations have an impaired inflammatory response to various stimuli. To date, molar tissues analyzed from patients with NLRP7 mutations have been found to be diploid and biparental. In this study, we report 10 new non-synonymous variants and one stop codon found in patients and not in controls. We demonstrate the presence of different types of moles, diploid biparental, diploid androgenetic, triploid and tetraploid conceptions, in patients with NLRP7 variants. We document in vitro and in vivo early embryo cleavage abnormalities in three patients. We propose a two-hit mechanism at the origin of androgenetic moles. This mechanism consists of variable degrees of early embryo cleavage abnormalities leading to chaotic mosaic aneuploidies, with haploid, diploid, triploid and tetraploid blastomeres. Surviving embryonic cells that reach implantation are then subject to the maternal immune response. Because of the patients' impaired inflammatory response, androgenetic cells, which are complete allograft, are able to grow and proliferate. In women with normal immune system, chaotic mosaic aneuploidies may also occur during early cleavage, however, androgenetic cells would die after implantation or stay undetected, confined to a small portion of the placenta.

Gestational trophoblastic diseases: recent advances in histopathologic diagnosis and related genetic aspects

Gestational trophoblastic disease refers to a spectrum of proliferative disorders of the placental trophoblast, with a wide range of histologic appearances and clinical behaviors. This review discusses the more recent developments in the diagnosis of these entities. Changes in criteria for the histologic diagnosis of these lesions due to earlier clinical diagnosis are reviewed, and the ability to make more accurate diagnoses due to the introduction of newer antibodies such as p57 is highlighted. A discussion of epithelioid trophoblastic tumor, a newly introduced tumor subtype, with its differential diagnosis from placental-site trophoblastic tumor and squamous cell carcinoma is also presented. Last, a brief discussion on the role of genetic studies and the future direction of research in elucidating the nature of this intriguing group of lesions is presented.

Cytokeratin 20 as a biomarker of gestational trophoblastic disease: diagnostic and prognostic significance

OBJECTIVES

This study was designed to examine whether cytokeratin 20 (CK20) is expressed in molar pregnancies and may therefore be used in the diagnosis of gestational trophoblastic disease (GTD). The potential of CK20 expression in predicting the evolution and the prognosis of the different subtypes of GTD was also assessed.

METHODS

A total of 48 samples were studied for CK20 expression by RT-PCR methodology. Among these, 24 samples were obtained by curettage of the uterine cavity of patients diagnosed with hydatidiform mole (14 complete moles and 10 partial moles), 4 samples were obtained from choriocarcinoma cell lines (2 JAR and 2 JEG), and 20 samples were of normal trophoblast (control group) obtained from patients that underwent elective termination of pregnancy.

RESULTS

Expression of CK20 was identified in all the samples of complete mole (CM), all choriocarcinoma cell lines, and 50% of the patients with partial mole (PM). None of the preparations of normal trophoblastic tissue from the control group expressed the CK20. A significant difference (P < 0.00001) was found in CK20 expression between samples of patients with GTD and control samples. Comparison between CK20 expression in CMs and PMs revealed a significantly more frequent expression of CK20 in CMs (P = 0.006). More than 50% of the patients with PMs that were positive for CK20 had an invasive evolution.

CONCLUSIONS

In our opinion, CK20 may assist in distinguishing between molar and normal trophoblastic tissue and may be considered a marker of GTD. In cases in which pathological classification of different subtypes of GTD is in doubt, CK20-positive expression is suggestive for a CM whereas CK20-negative is more indicative for PM.