Tetraploid partial hydatidiform moles: two cases with a triple paternal contribution and a 92,XXXY karyotype

Androgenetic/biparental mosaicism in a diploid mole-like conceptus: report of a case with triple paternal contribution

Hydatidiform moles (HMs) are divided into two types: partial hydatidiform mole (PHM) which is most often diandric monogynic triploid and complete hydatidiform mole (CHM) which is most often diploid androgenetic. Morphological features and p57 immunostaining are routinely used to distinguish both entities. Genetic analyses are required in challenging cases to determine the parental origin of the genome and ploidy. Some gestations cannot be accurately classified however. We report a case with atypical pathologic and genetic findings that correspond neither to CHM nor to PHM. Two populations of villi with divergent and discordant p57 expression were observed: morphologically normal p57 + villi and molar-like p57 discordant villi with p57 + stromal cells and p57 - cytotrophoblasts. Genotyping of DNA extracted from microdissected villi demonstrated that the conceptus was an androgenetic/biparental mosaic, originating from a zygote with triple paternal contribution, and that only the p57 - cytotrophoblasts were purely androgenetic, increasing the risk of neoplastic transformation.

Challenges in diagnosing hydatidiform moles: a review of promising molecular biomarkers

INTRODUCTION

Hydatidiform moles (HMs) are pathologic conceptions with unique genetic bases and abnormal placental villous tissue. Overlapping ultrasonographical and histological manifestations of molar and non-molar (NM) gestations and HMs subtypes makes accurate diagnosis challenging. Currently, immunohistochemical analysis of p57 and molecular genotyping have greatly improved the diagnostic accuracy.

AREAS COVERED

The differential expression of molecular biomarkers may be valuable for distinguishing among the subtypes of HMs and their mimics. Thus, biomarkers may be the key to refining HMs diagnosis. In this review, we summarize the current challenges in diagnosing HMs, and provide a critical overview of the recent literature about potential diagnostic biomarkers and their subclassifications. An online search on PubMed, Web of Science, and Google Scholar databases was conducted from the inception to 1 April 2022.

EXPERT OPINION

the emerging biomarkers offer new possibilities to refine the diagnosis for HMs and pregnancy loss. Although the additional studies are required to be quantified and investigated in clinical trials to verify their diagnostic utility. It is important to explore, validate, and facilitate the wide adoption of newly developed biomarkers in the coming years.

Gestational Trophoblastic Disease: Contemporary Diagnostic Approach

Pathologic diagnosis of gestational trophoblastic disease (GTD)-hydatidiform moles and gestational trophoblastic neoplasms-underwent a major shift in the past decade from morphology-based recognition to precise molecular genetic classification of entities, which also allows for prognostic stratification of molar gestations. This article highlights these recent advances and their integration into the routine pathology practice. The traditional gross and histomorphologic features of each entity are also reviewed with special focus on differential diagnoses and their clinical implications.

Genotyping diagnosis of gestational trophoblastic disease: frontiers in precision medicine

Investigations in recent decades have exploited tissue DNA genotyping as a powerful ancillary tool for the precision diagnosis and subclassification of gestational trophoblastic disease. As lesions of gestational origin, the inherited paternal genome, with or without copy number alterations, is the fundamental molecular basis for the diagnostic applications of DNA genotyping. Genotyping is now considered the gold standard in the confirmation and subtyping of sporadic hydatidiform moles. Although a precise diagnosis of partial mole requires DNA genotyping, prognostic stratification according to distinct genetic zygosity in complete moles has recently gained significant clinical relevance for patient care. Beyond hydatidiform moles, DNA genotyping has fundamental applications in the diagnosis or prognostic assessment of gestational trophoblastic tumors, in particular gestational choriocarcinoma. DNA genotyping provides a decisive tool in the separation of gestational trophoblastic neoplasia from non-gestational counterparts/mimics of either germ cell or somatic origin. The FIGO/WHO prognostic scoring scheme requires ascertaining the precise index gestational event and the time interval between the tumor and index gestation, where DNA genotyping can provide highly relevant information. With rapid acquisition of molecular diagnostic capabilities in the clinical practice, DNA genotyping has become closely integrated into the routine diagnostic workup of various forms of gestational trophoblastic disease.

Trophoblast inclusions in the human placenta: Identification, characterization, quantification, and interrelations of subtypes

We sought to examine placentas enriched for trophoblast inclusions (TIs) in order to characterize, quantify, and examine the interrelations between subtypes of TIs to better understand their underlying biology. We examined a cohort of 600 placentas from deliveries between 200 and 430 weeks of gestation. Forty-five percent of the placentas had at least one TI in the two slides examined. Four percent of the placentas had 10 or more TIs and two placentas had more than 70 TIs. Four distinct TI subtypes were observed: inclusionoids (early forming inclusions), inclusions, calcified inclusions, and calcified bodies. We suggest this reflects a developmental trajectory of TI maturation, the timing of which might be useful when comparing TI expression to clinical outcomes.

A 92,XXXY Miscarriage Consecutive to a Digynic Triploid Pregnancy

The patient was referred for prenatal diagnosis due to the sonographic finding of a polymalformed male fetus, and an amniocentesis was performed before termination of pregnancy. The pathological study of the placenta did not show morphological alterations. In her next pregnancy, sonographic examination disclosed a missed abortion with a visible embryo, and a chorionic villi sample was obtained for cytogenetic analysis before evacuation. Macroscopic examination of the villi sample did not reveal molar vesicular appearance. QF-PCR and cytogenetic analyses were performed on amniotic fluid (first pregnancy) and chorionic villi samples (second pregnancy). A 69,XXY and 92,XXXY karyotype was found, respectively. QF-PCR results disclosed 2 maternal and 1 paternal alleles in the first pregnancy (digynic triploidy), and double maternal and double paternal contribution to the tetraploid pregnancy. Among the few reported cases of 92,XXXY tetraploidy, those associated with partial moles show a PPPM genotype (3 paternal and 1 maternal alleles), and the only case with a PPMM genotype was found in a spontaneously aborted fetus similar to our case. We are not aware of other cases with combination of a digynic triploid pregnancy and a tetraploid pregnancy with a PPMM contribution. Our case adds evidence to the influence of the balance between paternal and maternal genomic doses on the phenotype.

NLRP7 and the Genetics of Hydatidiform Moles: Recent Advances and New Challenges

NOD-like receptor proteins (NLRPs) are emerging key players in several inflammatory pathways in Mammals. The first identified gene coding for a protein from this family is Nlrp5 and was originally called Mater for “Maternal Antigen That Mouse Embryos Require” for normal development beyond the two-cell stage. This important discovery was followed by the identification of other NLRPs playing roles in inflammatory disorders and of the first maternal-effect gene in humans, NLRP7, which is responsible for an aberrant form of human pregnancy called hydatidiform mole (HM). In this review, we recapitulate the various aspects of the pathology of HM, highlight recent advances regarding NLRP7 and its role in HM and related forms of reproductive losses, and expand our discussion to other NLRPs with a special emphasis on those with known roles in mammalian reproduction. Our aim is to facilitate the genetic complexity of recurrent fetal loss in humans and encourage interdisciplinary collaborations in the fields of NLRPs and reproductive loss.

Combination of immunohistochemistry and ploidy analysis to assist histopathological diagnosis of molar diseases

Background:

Differential diagnosis between hydropic abortion, partial mole and complete mole is still a challenge for pathologists but really important for patient management.

Material and Method:

In this study, we have evaluated 111 products of conception from the first trimester. Histological analysis was made according to the main diagnostic histopathological features described in the literature and the cases were categorized in hydropic abortus (HA), partial mole (PM) and complete mole (CM). Immunohistochemistry was performed using monoclonal antibody against p57^kip protein a putative paternally imprinted inhibitor gene and DNA ploidy was analysed in all cases by image cytometry.

Results:

All 23 HAs presented a diploid DNA content and were p57^kip2 positive. From the 28 CMs, 12 cases (43%) were diploid and 16 cases (57%) were tetraploid but no expression of p57^kip2 was found with positive internal controls. From the 60 PMs, 58 cases were positive for p57^kip2 expression and 53 cases (88%) were triploid, 6 cases (10%) tetraploid and 1 case (2%) diploid.

Conclusion:

This study on 111 cases of early pregnancies confirms the usefulness of immunohistochemistry and cytometry but demonstrates the importance of the combination of both techniques to assist histology for the best reliable diagnosis.

[Abnormal placental caryotype in severe intrauterine growth retardations (IUGR). Case report]

Except for cases due to maternal hypertension, severe and early intrauterine growth retardations are most usually due to fetal abnormalities. We report a case of confined placental homogenous tetraploidy associated with major fetal growth retardation leading to the premature delivery of a life born baby with a normal caryotype. We discuss the interest of chorionic villus sampling in cases of unexplained severe fetal growth retardation.

Differences in current clinical features of diploid and triploid hydatidiform mole

OBJECTIVE

To describe and compare the current clinical features of diploid and triploid molar pregnancy and to evaluate whether the presenting clinical features can predict the ploidy of a molar pregnancy.

DESIGN

A retrospective study of the clinical features and ploidy of hydatidiform moles.

SETTING

The Departments of Clinical Genetics and Pathology, Aarhus University Hospital and 13 gynaecological wards, Jutland, Denmark.

POPULATION

A total of 259 women with molar pregnancy diagnosed between April 1986 and June 2003.

METHODS

A review of medical records of consecutively collected, clinically suspected cases of molar pregnancy was performed. The molar ploidy was determined by karyotyping, flow cytometry, and/or analysis of polymorphic DNA markers.

MAIN OUTCOME MEASURES

Maternal characteristics, presenting symptoms, initial human chorionic gonadotrophin (hCG), and molar ploidy.

RESULTS

In a multiple logistic regression model, initial hCG of > or = 100,000 iu/l (P < 0.001), first-trimester gestational age (P < 0.001), vaginal bleeding (P < 0.001), and maternal age of > or = 40 years (P = 0.03) were independent predictors of diploid mole. Women with excessive uterine size more frequently had a diploid than a triploid mole (P < 0.001). Fifty-four percent of the women with triploid mole and 27% of the women with diploid mole were diagnosed before onset of symptoms (P < 0.001).

CONCLUSIONS

The current clinical features of diploid mole are different from those of triploid mole. The presenting clinical profile of a molar pregnancy may be used as an early predictor of the molar ploidy and thus of the prognosis.

Tetraploid development in the mouse

Spontaneous duplication of the mammalian genome occurs in approximately 1% of fertilizations. Although one or more whole genome duplications are believed to have influenced vertebrate evolution, polyploidy of contemporary mammals is generally incompatible with normal development and function of all but a few tissues. The production of tetraploid (4n) embryos has become a common experimental manipulation in the mouse. Although development of tetraploid mice has generally not been observed beyond midgestation, tetraploid:diploid (4n:2n) chimeras are widely used as a method for rescuing extraembryonic defects. The tolerance of tissues to polyploidy appears to be dependent on genetic background. Indeed, the recent discovery of a naturally tetraploid rodent species suggests that, in rare genetic backgrounds, mammalian genome duplications may be compatible with the development of viable and fertile adults. Thus, the range of developmental potentials of tetraploid embryos remains in large part unexplored. Here, we review the biological consequences and experimental utility of tetraploid mammals, in particular the mouse.

Immunohistochemical Characterization of p57Kip2 Expression in Tetraploid Hydropic Placentas

Context.—Because there are differences in the origin, morphology, and natural history of hydropic placental villous issues, it is important to identify and document rare specimens that deviate from the diploid complete hydatidiform mole (CM), triploid partial hydatidiform mole (PM), or diploid hydropic abortion (HA). Tetraploid hydropic placentas have rarely been studied.

Objectives.—To evaluate the frequency of p57Kip2 protein (p57) expression in tetraploid hydropic placentas and to determine its clinicopathologic significance.

Design.—Forty hydropic DNA tetraploid placental specimens were evaluated by immunohistochemistry of formalin-fixed tissues, using a monoclonal antibody against p57, a putative paternally imprinted inhibitor gene. DNA ploidy in all cases was analyzed by flow cytometry.

Results.—Thirty cases were histologically diagnosed as CMs, 10 were HAs, and none were PMs. In all HAs, nuclear p57 was strongly expressed in cytotrophoblasts, intermediate trophoblasts, and villous stromal cells. In contrast, in CMs, p57 expression in cytotrophoblasts and villous stromal cells was either absent (26 cases) or very low (4 cases). Assuming that the degree of molar change roughly correlates with the proportion of paternal chromosomes present, all chromosomes might be paternally derived in all tetraploid CMs and the 10 HAs, including 2 that were karyotyped as 92,XXYY or 90,XXYY,−13,−14, which were presumably due to 2 sets of chromosomes each from paternal and maternal origin.

Conclusions.—Expression of p57 is aberrant in tetraploid CMs. This finding is in line with the hypothesis that the loss of p57 is involved in the abnormal development of androgenetic CMs. For the evaluation of a patient with trophoblastic disease, p57 immunostaining is an ancillary diagnostic method that may be used in concert with flow cytometry.

Genetics and molecular markers in gestational trophoblastic disease with special reference to their clinical application

Gestational trophoblastic disease (GTD) encompasses a diverse group of lesions with specific cytogenetic and molecular pathogenesis. Although cytogenetic studies have been extensively reported, the molecular pathogenesis is poorly understood. We will summarize some of the recent molecular observations and correlate them with the pathology of GTD. Complete mole is androgenetic in origin. Thus, if a monoallelic contribution can be shown in complete mole, this would render the gene susceptible to functional inactivation by 'one-hit' kinetics. Alternatively, uniparental transmission of genes that are subject to parental imprinting in humans would impair their regulation. Loss of NECC1 expression, biallelic deletions at the critical (7p12-7q11.23) region and enhanced H19 expression in choriocarcinoma would reflect the genetic features exhibited by the putative forerunner, complete mole. In addition to the unique genetic features shown in GTD, alterations in gene expression profiles accompanied by malignant conversion of trophoblasts would facilitate the development of choriocarcinogenesis from complete mole. With recent advances in molecular techniques, further work is still necessary to provide a better understanding and useful markers for persistent trophoblastic disease. These may provide useful prognostic indications that may guide the different diagnosis of GTD.

A tetraploid liveborn neonate: cytogenetic and autopsy findings

Cytogenetic and autopsy findings of a nonmosaic tetraploid male neonate, alive until shortly after birth at 37 weeks' gestation, are described. Oligohydramnios, intrauterine growth retardation, cranial abnormalities, and Dandy-Walker malformation were noted prenatally. Autopsy findings included cleft lip and palate; overlapping fingers; low-set ears; simian creases; hypoplastic external genitalia with undescended testes; Dandy-Walker malformation; slightly dilated lateral and third ventricles; hypoplasia of the cerebrum, pons, medulla, pituitary gland, thymus, lung, adrenal gland, and kidney; large ventricular septal defect; and enteric cyst behind the urinary bladder. The placenta was hypoplastic and showed no remarkable abnormalities, except for mild syncytial knots. Chromosome analyses of amniotic fluid cells at 31 weeks' gestation and the umbilical cord blood cells at delivery revealed a 92,XXYY karyotype. G-, C-, Q-, and N-banding heteromorphic studies demonstrated duplication of paternal chromosomes 1, 3, and 15, and maternal chromosome 22. In addition, the results of an analysis with 16 CA repeat polymorphic markers were consistent with duplicated inheritance of 1 paternal and 1 maternal haploid sets to the tetraploid patient. Therefore, it is most likely that the tetraploidy was caused by a cytoplasmic cleavage failure at the first mitotic division.

Histopathological diagnosis of partial and complete hydatidiform mole in the first trimester of pregnancy

The diagnosis of molar pregnancy is a continuing diagnostic problem for many practicing histopathologists who are required to examine specimens of products of conception, particularly since changes in gynecological management in recent years have resulted in uterine evacuation at earlier gestations. The aim of this review is to provide practical, up-to-date, diagnostically useful information regarding the histological diagnosis of molar disease in early pregnancy. Pathophysiological issues relevant to molar pregnancies, such as genetic abnormalities, will be briefly summarized, but nonhistopathological aspects of molar disease will not be covered in detail in this review.

Paternal origins of complete hydatidiform moles proven by whole genome single-nucleotide polymorphism haplotyping

Complete hydatidiform moles (CHMs) are diploid tumors that result from fertilization of an empty ovum by a haploid 23,X sperm. In most cases, the resulting duplication of the genome gives rise to a 46,XX genotype and is thought to be androgenetic in origin. If this hypothesis is correct, then the genotypes of all polymorphic markers in CHMs should be homozygous. We used a dense set of single-nucleotide polymorphism (SNP) markers, evenly spaced throughout the genome, to definitively test this hypothesis. We genotyped genomic DNA samples from five CHMs and their corresponding maternal samples with 1494 SNP markers using high-density microarrays (HuSNP). As predicted, the maternal samples were heterozygous at >25% of the markers, which is consistent with the expected average heterozygosity of this panel of SNPs. In contrast, the five CHM samples were heterozygous at <0.75% of the SNP markers, which shows that these diploid tumors consist of a duplicated set of chromosomes. Because the CHM genotypes represent the haplotypes of their genomes, our results show that long-range haplotypes can be obtained easily with this resource and that a collection of such samples is a simple way to obtain reference haplotypes for association studies in various populations.

Flow cytometric and clinicopathologic study of complete hydatidiform moles with special reference to the significance of cytometric aneuploidy

OBJECTIVE

As complete hydatidiform moles (CMs) have been studied less with respect to aneuploidy and its clinical implications, the significance of cytometric aneuploidy in CMs was evaluated.

METHODS

Two hundred thirty-nine CMs were studied clinicopathologically and analyzed by flow cytometry using formalin-fixed paraffin-embedded tissues.

RESULTS

Of 239 CMs, 182 were diploid, 30 were tetraploid, and 27 were aneuploid (nontriploid/tetraploid aneuploid). There were no significant histologic differences among the diploid, tetraploid, and aneuploid CMs. Persistent disease developed in 20 of 114 CMs (17.6%) (16 of 77 diploid, 4 of 18 tetraploid, and none of 19 aneuploid CMs). Eight diploid and three tetraploid CMs were invasive, and one patient each with diploid CM and tetraploid CM developed choriocarcinoma and none of 19 patients with aneuploid CMs had sequelae.

CONCLUSION

These results suggest that aneuploid CMs are associated with less risk for persistent disease than diploid or tetraploid CMs. DNA ploidy status may be an independent predictor of persistent disease.

Molecular identification of a partial hydatidiform mole

Specimens of a vacuum curettage were microscopically indicated for a hydatidiform mole. The combination of three different approaches identified the specimen as a partial mole caused by the fertilization of a haploid ovum by sperm containing a haploid or diploid nucleus with one or two sets of paternal genetic material. Interphase fluorescence in situ hybridization identified three chromosome 1 centromeres, and DNA flow cytometry revealed a peak with a DNA index of 1.50. The combination of flow cytometric cell sorting and microsatellite marker polymerase chain reaction proved that in this case two alleles were from paternal origin. Because it is known that partial hydatidiform moles have a tendency for recurrence, specimens from the same patient of an earlier executed vacuum curettage were investigated. Microdissection of the villi was performed before DNA isolation in this case as too few villi were present for DNA flow cytometry and cell sorting. In this case, no evidence was fond for additional alleles. This study shows the diagnostic potential of microsatellite markers for genetic typing of hydatidiform moles.

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

In order to evaluate the significance of cytometric aneuploidy in molar placentas, we analyzed 197 hydatidiform moles by flow cytometry using formalin-fixed, paraffin-embedded tissues. Of 150 complete moles (CMs), 110 were diploid, 26 were tetraploid, and 14 were aneuploid (non-triploid/tetraploid aneuploid). Of 47 partial moles (PMs), 44 were triploid and 3 were diploid. We could not find any histologic differences among the diploid, tetraploid, and aneuploid CMs. We found that flow cytometric DNA analysis was very helpful to differentiate CM from PM. Persistent diseases developed in 12 of 69 CMs (17.4%) (9 of 47 diploid and 3 of 14 tetraploid CMs) and in none of 26 PMs (0%). Four diploid and 2 tetraploid CMs were invasive and one each with diploid and tetraploid CM developed choriocarcinoma and none of 8 aneuploid CMs had sequelae; however, there was no correlation between DNA ploidy and clinical outcome in the CMs. These results suggest that cytometric aneuploidy (non-diploidy) in CMs is not an independent predictor of persistent disease.

Distinctive flow histogram pattern in molar pregnancies with elevated maternal serum human chorionic gonadotropin levels

BACKGROUND

Flow cytometric analysis of trophoblastic tissue has shown that most partial hydatidiform moles (PMs) are triploid, whereas most complete moles (CMs) are diploid or tetraploid. Ploidy analysis can support a diagnosis of CM or PM. However, in some cases, a precise diagnosis cannot be rendered.

METHODS

This study examined DNA flow histograms in 86 cases of histologically diagnosed moles and nonmoles to identify patterns specific to moles to eliminate indeterminate diagnoses. Forty hydropic abortions, 17 CMs, and 29 PMs were analyzed, and results were correlated with microscopic appearance and maternal serum human chorionic gonadotropin (HCG) levels.

RESULTS

Analysis of nondiploid histologic moles in which the initial maternal serum HCG level was greater than 150,000 mIU/ml showed similar histograms in 12 of 14 cases. In these 12 specimens, a distinct aneuploid peak could not be delineated from multiple cell populations between the G0/G1 and G2/M or G0/G1diploid and G0/G1aneuploid peaks. This commonly appeared as a slope rising toward the tetraploid region. S-phase fraction values showed a trend toward higher values in the moles versus nonmoles, but the difference was not statistically significant.

CONCLUSIONS

This sloping histogram pattern may reflect progression from a single aneuploid to multiple aneuploid populations. Its statistically significant correlation (P < 0.001) with high maternal serum HCG values suggests the presence of a highly metabolically active population of aneuploid trophoblast. Because it appears specific to nondiploid moles, recognition of the pattern will aid in the distinction of mole from hydropic spontaneous abortion.

Prenatal diagnosis of tetraploidy: a case report

We report on the second trimester prenatal diagnosis of an apparently nonmosaic tetraploid fetus, 92,XXYY. Indications for cytogenetic studies of the fetus included abnormal ultrasound findings and abnormal maternal serum levels of alpha-fetoprotein (AFP)/estriol. Chromosome analysis of amniocytes documented tetraploidy, a finding confirmed by flow cytometry of several fetal tissues. Autopsy findings in the fetus are compared with those of other cases of tetraploidy. To our knowledge this is the first reported prenatal diagnosis of a tetraploid fetus. Additionally, it illustrates the value of flow cytometric analysis of products of conception in which polyploidy is suspected.

Electrofusion of mouse embryos results in uniform tetraploidy and not tetraploid/diploid mosaicism

Some previous attempts to produce tetraploids experimentally have resulted in a proportion of treated embryos becoming 2n/4n mosaics at a frequency which may be as high as 20%, when using cytochalasin B as a fusigenic stimulus and cytogenetic techniques to identify putative tetraploid embryos. To investigate the possible occurrence of 4n/2n mosaicism, tetraploid embryos were produced by electrofusion, a process which allows adjacent blastomeres at the 2-cell stage to fuse following exposure to electric field pulses. Embryos used for electrofusion were hemizygous for a transgene consisting of approximately 1000 copies of the mouse beta-globin gene. After in situ hybridization, one hybridization signal is expected per diploid genome. Tetraploid cells in 7.5-, 8.5-, 9.5- and 10.5-day-old conceptuses were distinguished from diploid cells by performing in situ hybridization on histological sections. The frequency of nuclei with two hybridization signals in the 'hemizygous' tetraploid embryos was compared to diploid embryos which were either hemizygous or homozygous for the beta-globin transgene. Comparison of the frequency of nuclei with two hybridization signals between tissues of 'hemizygous' tetraploid conceptuses and homozygous diploid conceptuses showed no significant difference, which implies that the tissues in the tetraploid conceptuses were uniformly tetraploid. No evidence was found to suggest that electrofusion results in 2n/4n mosaicism.

The immune system in disease: gestational trophoblastic tumours

Trophoblastic tumours form a spectrum of disease from the borderline malignancy of HM to highly aggressive choriocarcinoma. Their management requires the integration of the information derived from serial hCG estimations, the clinical history and pattern of spread of the disease, so that our understanding of the prognostic variables can be applied appropriately. This maximizes the patient's chances of complete remission from her disease with the minimum of toxicity. Given our knowledge of this group of diseases and an integrated approach to management, it should be uncommon for any woman to die from her trophoblastic tumour.

A genetic review of complete and partial hydatidiform moles and nonmolar triploidy

Complete and partial hydatidiform moles are genetically aberrant conceptuses. Usually, complete moles have 46 chromosomes (diploidy), all of paternal origin. Most partial moles have 69 chromosomes (triploidy), including 23 of maternal origin and 46 of paternal origin. Triploidy that involves 23 paternal chromosomes and 46 maternal chromosomes is not associated with molar placental changes and, rarely, can result in a live-born infant with multiple birth defects. Herein we review the mechanisms of fertilization that may produce these unbalanced sets of parental chromosomes and the role of genomic imprinting as a possible explanation for these clinical conditions.

The differential staining pattern of the X chromosome in the embryonic and extraembryonic tissues of postimplantation homozygous tetraploid mouse embryos

(C57BL x CBA)F1 hybrid female mice were mated with hemizygous Rb(X.2)2Ad males to distinguish the paternal X chromosome. Homozygous tetraploids were produced by blastomere fusion at the 2-cell stage, and 161 of these were transferred to recipients and analysed on the 10th day of gestation. 59 implants contained resorptions and 76 contained either an embryo and/or extraembryonic membranes. 38 (20, XXXX and 18, XXYY) were analysed to investigate their X-inactivation pattern. Embryonic and yolk sac endodermally- and mesodermally-derived samples were analysed by G-banding and by Kanda analysis. In the XX and XY controls, the predicted pattern of X-inactivation was observed, though 12.2% of metaphases in the XX series displayed no X-inactivation. In the XY series the Y chromosome was seen in a high proportion of metaphases. In the XXXX tetraploids, 8 cell lineages were recognized with regard to their X-inactivation pattern, though most belonged to the following 3 categories: (XmXm)XpXp, Xm(XmXp)Xp and XmXm(XpXp). The other categories were only rarely encountered. In the embryonic and mesodermally-derived tissue the ratio of these groups was close to 1:2:1, whereas in the endodermally-derived tissue it was 1:4.11:4.88, due to preferential paternal X-inactivation. A significant but small proportion of all 3 tissues analysed displayed no evidence of X-inactivation. Indirect evidence suggests that this represents a genuine group because of the high efficiency of the Kanda staining. The presence of the Xm(XmXp)Xp category is consistent with the expectation that X-inactivation occurs randomly in 2 of the 4 X chromosomes present. The presence of small numbers of preparations with no evidence of X-inactivation and other unexpected categories suggests that these are probably selected against during development.

Persistent gestational trophoblastic disease following evacuation of a tetraploid partial hydatidiform mole

A 31-year-old woman at 11 weeks gestation with ultrasonographic demonstration of partial mole had markedly elevated serum bHCG levels (458,000 mIU/ml). The patient underwent a vacuum curettage with pathological confirmation of the diagnosis, and cytogenetic analysis revealed a tetraploid karyotype (92,XXXX). The patient developed persistent gestational trophoblastic disease and was successfully treated with two courses of actinomycin D. Persistent trophoblastic disease after evacuation of a tetraploid partial mole was not reported previously.

Interphase cytogenetics in paraffin sections of routinely processed hydatidiform moles and hydropic abortions

The differential diagnosis of complete (CM) and partial (PM) hydatidiform moles and hydropic abortions (HA) can be difficult when based on histology alone. Therefore, a more objective approach of chromosome ploidy analysis as detected by in situ hybridization (ISH) was performed on 6 microns paraffin sections of seven cases, originally classified as three CM, two PM, and two HA with a histologic pattern suggestive of triploidy. Probes for repetitive DNA targets in the (peri)centromeric region of chromosomes 1 and X and in the q arm of chromosome Y were used to determine chromosome ploidy and sex chromosome composition. The findings in the three CM were consistent with diploidy: two copies of chromosomes 1 and X and none of chromosome Y. In the two HA with a histologic pattern suggestive of triploidy, three copies of chromosomes 1 and X and none of chromosome Y confirmed triploidy. Two cases originally classified as PM both appeared to have two copies of chromosome 1 with an XX pattern in one case and an XY pattern in the other case, which is consistent with diploidy instead of triploidy. After reviewing, both cases most likely represented CM. We conclude that interphase cytogenetics by ISH on paraffin sections of hydatidiform moles and hydropic abortions enables chromosome ploidy analysis with preservation of histological context.(ABSTRACT TRUNCATED AT 250 WORDS)

Current topic: trophoblastic pathology

Selected topics in trophoblastic pathology which are arousing current interest are briefly reviewed. These include the concept of villitis as a non-specific immunological lesion, changing views on the distinction between partial and complete hydatidiform mole, a reconsideration of the role of inadequate placentation in pregnancy hypertension and in spontaneous abortion, the significance of confined placental mosaicism and the importance of infection and defective collagen synthesis in premature rupture of the membranes.

Two different phenotypes of fetuses with chromosomal triploidy: correlation with parental origin of the extra haploid set

Triploidy is a condition in which there is over-representation of one parental genome. Recent work in experimental mouse embryo-genesis suggests that the parental origin of the extra genome in triploidy may have specific effects on both embryonic/fetal phenotype and placental development due to an "imprinting" effect. We studied 19 human triploid fetuses and discerned 2 distinct fetal phenotypes, as well as the previously described placental phenotypes, which correlate with the parental origin of the extra haploid set. Although these findings suggest that in human triploids the parental origin of the extra haploid set is important in determination of both fetal and placental phenotype it is not clear to what degree placental development and function affect the resultant fetal phenotype.

Triploidy arising from a first meiotic non-disjunction in a mother carrying a reciprocal translocation

We report on a 22 year old mother, a carrier of a 6;14 balanced reciprocal translocation, who aborted a triploid conceptus carrying a similar translocation. We showed the maternal origin of this triploidy, after non-disjunction at meiosis I. The phenotypic expression as a non-molar pregnancy, the contribution of the maternal translocation, and possible aetiological factors of triploidy are discussed.

Frequency of heterozygous complete hydatidiform moles, estimated by locus-specific minisatellite and Y chromosome-specific probes

Restriction fragment length polymorphisms identified with three locus-specific minisatellite probes and banding patterns with Y chromosome-specific probes have been examined in 39 cases of complete hydatidiform mole (CHM) and the parents. All 39 cases were shown to be androgenetic. Of the 39 cases, 8 were identified as heterozygous CHM using the minisatellite probes. Estimates for the total number of heterozygous CHM in the series ranged from 23%-29%, higher than previously reported. Of the eight identified heterozygous CHM, six had Y chromosome-specific sequences whereas two were female; this is not significantly different from the 2:1 ratio expected. The low frequency of 46,XX heterozygous CHM in the literature may reflect difficulties in distinguishing them from 46,XX homozygous CHM. Examination of RFLPs with a small panel of locus-specific minisatellite probes provides a powerful method of classifying hydatidiform mole, enabling the rare heterozygous 46,XX CHM to be accurately identified.

The biology of tetraploid hydatidiform moles: histopathology, cytogenetics, and flow cytometry

We identified three cases of tetraploid hydatidiform moles (HM). A complete hydatidiform mole (CM) had a 92,XXXX karyotype. The two partial hydatidiform moles (PM) had karyotypes of 69,XXY/90,XXXY,-11,-13 and 92,XXYY, respectively. Study of chromosomal heteromorphisms in the 92,XXYY PM revealed two maternal and two paternal haploid sets. Flow cytometric analysis of nuclear DNA content from fresh placental tissue from the 69,XXY/90,XXXY,-11,-13 PM demonstrated distinct peaks in the triploid and tetraploid regions and an octaploid G2/M peak. Flow cytometric analysis of paraffin-embedded, fixed tissue was diagnostic of tetraploidy in the 92,XXXX CM and consistent with tetraploidy in the 92,XXYY PM. All three patients achieved spontaneous remission of elevated gonadotropin levels. These three cases of tetraploid HM do not fit into the usual patterns of diploid CM and triploid PM. We conclude that flow cytometric analysis of nuclear DNA may be used to identify polyploidy in fresh and paraffin-embedded, fixed placental tissues. Categorization of all molar placentas on the basis of ploidy presents rare opportunities to study the biology and natural history of gestational trophoblastic disease in tetraploid HM.

Genetically different cell subpopulations in hydatidiform moles. A study of three cases by RFLP, flow cytometric, cytogenetic, HLA, and morphologic analyses

Most investigators find a good correlation between the morphologic and cytogenetic classification of hydatidiform moles (HM), but exceptions have been noted. We have examined three cases of HM, using chromosome marker analysis on cultured cells, human leukocyte antigen typing on cultured and uncultured tissue, and restriction fragment length polymorphism (RFLP) analysis and flow cytometry on uncultured cells. In one morphologically partial mole, only one cell population (triploid) was found and data obtained by the above-mentioned techniques were concordant. The other two moles, which were classified morphologically as complete, consisted of several cell subpopulations differing in DNA content. In both cases only one cell population was disclosed by cytogenetic investigation. In one case, the cytogenetic analysis indicated that the cultured cells were near triploid with paternal chromosomes exclusively, whereas RFLP analysis showed that maternal X chromosomal alleles were present in the mole. The present findings demonstrate that some HMs contain cellular subpopulations with differing DNA content. One explanation for discordance between cytogenetic and morphologic classification may thus be the detection of only one cell subpopulation when karyotyping.

Hydatidiform mole: cytogenetically unusual cases and their implications for the present classification

Unusual observations in hydatidiform moles are of clinical importance as well as of theoretical interest when the present subgrouping into partial or complete moles is evaluated, particularly in view of the more malignant potential of the latter. The purpose of the present review is to summarize, update, and evaluate information on moles with unusual karyotypes or origins. The important factor in the evolution of partial or complete moles appears to be the ratio of maternal to paternal chromosomes and not the ploidy of the tissue. Complete hydatidiform moles develop from androgenetic conceptions while partial hydatidiform moles develop from those conceptions in which the number of paternal sets of chromosomes exceeds the number of maternally derived sets. Rare cases inconsistent with this concept emphasize the value of examining morphologic features, cell ploidy, and genetic markers when one is attempting to classify hydatidiform moles.

Diagnosis of molar pregnancy and persistent trophoblastic disease by flow cytometry

Histopathological assessment and flow cytometric analyses were carried out on 32 placentas (representative of each trimester) and 88 molar pregnancies. Three first trimester placentas were triploid, and the remaining 29 placentas were diploid. Of the 88 cases originally diagnosed as molar pregnancies, 26 were triploid (two complete moles, 20 partial moles, and four hydropic abortions); 59 were diploid (46 complete moles, 10 partial moles, three hydropic abortions); one was tetraploid (partial mole); and two were DNA aneuploid (one partial mole, one complete mole). A significantly increased hyperdiploid fraction (a measure of cell proliferation) was detected in diploid complete moles (p less than 0.0001) and cases of persistent trophoblastic disease (p less than 0.001) when compared with diploid placentas and diploid partial moles. All seven cases of established persistent trophoblastic disease, for which follow up was available, were diploid and showed high hyperdiploid fractions within the range for diploid complete moles. These findings suggest that flow cytometric DNA measurements may be an important aid in the diagnosis of molar pregnancy. The high degree of cell proliferation found in this study may explain the premalignant potential of complete hydatidiform moles.

Flow cytometry used to distinguish between complete and partial hydatidiform moles

Cells prepared from fresh tissue from a normal conception, and three complete hydatidiform moles (CHMs), were shown to be diploid by flow cytometry, while triploid populations were identified in tissue from two partial hydatidiform moles (PHMs). Similar results were found in cells from formalin-fixed, paraffin-embedded material. In nine cases where cytogenetic analysis was carried out this correlated with the results from flow cytometry. Using flow cytometry we were able to show that two cases which were pathologically complete were in fact diploid, despite the finding of trisomy at one locus in the molar tissue using biochemical markers. The most likely explanation of apparent trisomy of the enzymes in the molar tissue was contamination by maternal tissue.

Hydatidiform mole: genetic markers in diploid abortuses with macroscopic villous enlargement

In a series of diploid abortion specimens with gross villous enlargement the parental origin was determined by chromosomal heteromorphisms, HLA typing, and enzyme analysis. Diploid androgenesis was the mechanism in 33 cases; in 28 cases the most likely origin was by duplication of a haploid sperm after fertilization of an anucleated ovum, whereas heteromorphisms in five cases indicated a dispermic origin. In one macroscopically complete molar specimen all marker techniques applied indicated a normal conception. In two homozygous specimens a second cell line with both maternal and paternal contributions indicated a twin gestation, whereas, in four conceptuses twinning was suggested solely by HLA determination or ultrasound scan. The observation of a heterogeneous origin of diploid moles, as indicated by three marker systems studied simultaneously, emphasizes that additional information about the frequency of different types of molar conceptions may be obtained by this approach.

Genetic studies in hydatidiform mole with clinical correlations

In an elective study of 163 hydatidiform moles 38 were classified as partial mole (PHM) and 125 as complete mole (CHM) on the basis of pathology. Genetic studies showed the PHM to be triploid with one maternal and two paternal chromosome sets. In all cases of PHM the molar pregnancy resolved spontaneously after evacuation. On the basis of genetic studies CHM which were diploid could be subdivided into two entities: homozygous androgenetic CHMs that were 46,XX, and heterozygous CHMs which were androgenetic and usually 46,XY. In informative cases in this series the frequency of heterozygous CHM was 10 per cent. Twenty-two (17.6 per cent) of all the patients with CHM required subsequent chemotherapy for post-mole trophoblastic tumour. Where patients with CHM could be classified as having homozygous or heterozygous CHM the requirement for treatment (17.8 per cent and 25 per cent, respectively) was not found to be significantly different in the two groups.