Comprehensive genotype-phenotype correlations between NLRP7 mutations and the balance between embryonic tissue differentiation and trophoblastic proliferation.

BACKGROUND: Hydatidiform mole (HM) is a human pregnancy with excessive trophoblastic proliferation and abnormal embryonic development that may be sporadic or recurrent. In the sporadic form, the HM phenotype is driven by an abnormal ratio of paternal to maternal genomes, whereas in the recurrent form, the HM phenotype is caused by maternal-recessive mutations, mostly in NLRP7, despite the diploid biparental origin of the HM tissues. In this study, we characterised the expression of the imprinted, maternally expressed gene, CDKN1C (p57(KIP2)), the genotype, and the histopathology of 36 products of conception (POC) from patients with two defective alleles in NLRP7 and looked for potential correlations between the nature of the mutations in the patients and the various HM features. METHODS/RESULTS: We found that all the 36 POCs are diploid biparental and have the same parental contribution to their genomes. However, some of them expressed variable levels of p57(KIP2) and this expression was strongly associated with the presence of embryonic tissues of inner cell mass origin and mild trophoblastic proliferation, which are features of triploid partial HMs, and were associated with missense mutations. Negative p57(KIP2) expression was associated with the absence of embryonic tissues and excessive trophoblastic proliferation, which are features of androgenetic complete HMs and were associated with protein-truncating mutations. CONCLUSIONS: Our data suggest that NLRP7, depending on the severity of its mutations, regulates the imprinted expression of p57(KIP2) and consequently the balance between tissue differentiation and proliferation during early human development. This role is novel and could not have been revealed by any other approach on somatic cells.

Differential expression of E-cadherin, ß-catenin, and Lewis x between invasive hydatidiform moles and post-molar choriocarcinomas.

Trophoblast cell adhesion and migration are carefully coordinated during normal placental development. We have compared the expression of three adhesion molecules, E-cadherin, ß-catenin, and Lewis x, by immunohistochemistry during normal trophoblast differentiation, and in hydatidiform moles and choriocarcinomas. Both E-cadherin and ß-catenin were expressed in normal placenta cytotrophoblast, and this expression decreased with trophoblast maturation. E-cadherin was mainly localized along the contact between cytotrophoblast and syncytiotrophoblast, which indicates its role in the differentiation of the syncytial layer. Lewis x disappeared progressively during differentiation of normal villous vessels, and was expressed in molar pregnancies. Interestingly, whereas choriocarcinomas were not, or poorly, stained, invasive hydatidiform moles (invHMs) strongly expressed Lewis x in vascular structures. This observation correlated well with E-cadherin and ß-catenin expression and suggests that these three markers are associated with the invasive transformation. The presence of robust endothelial structures in invHMs could also explain their ability to maintain organized villous architecture (contrary to metastatic choriocarcinomas) during their invasion of extrauterine tissues such as the lung or the brain after dissemination through the blood flow. In our hands, Lewis x appeared to be a new, reliable marker that can be used to clearly distinguish invHMs from choriocarcinomas.

Altered p16 and Bcl-2 expression reflects pathologic development in hydatidiform moles and choriocarcinoma.

Abnormal trophoblast differentiation is the main cause of gestational trophoblast diseases in the case of hydatidiform moles and choriocarcinomas. Here we investigated the expression patterns of two gene products, p16 and Bcl-2, implicated in cell cycle regulation and apoptosis, respectively, using immunohistochemistry during normal placenta differentiation, hydatidiform moles (partial, complete and invasive) and post-molar choriocarcinomas. The p16 protein shows a gradual expression in cytotrophoblast of normal villous, from a p16 weak proliferative phenotype to a p16 strong invasive phenotype reaching a maximum around 17 weeks of gestation. The expression pattern in cytotrophoblast was similar in moles in contrast to the villous mesenchyme of invasive moles where p16 was strongly expressed. Bcl-2 expression was syncytiotrophoblast specific in normal placenta and moles and increased gradually during normal differentiation. The results explain the persistence of normal and molar villous fragments during their development and their dramatic invasion in the uterine arteries in case of invasive moles. In choriocarcinomas the weak Bcl-2 expression is associated with weak p16 expression indicating a great apoptotic and proliferative potentials. The results suggest that strong p16 expression in the villous mesenchyme may be responsible in part of the morbidity of the moles, and the key of cancer progression in the choriocarcinomas would be a fast cell-cycle turnover.

[Cytogenomic studies of hydatiform moles and gestational choriocarcinoma]. / Étude cytogénomique de la môle hydatiforme et du choriocarcinome gestationnel.

The complete hydatidiform mole (CHM), a gestational trophoblastic disease, is usually caused by the development of an androgenic egg whose genome is exclusively paternal. Due to parental imprinting, only trophoblasts develop in the absence of a fetus. CHM are diploid and no abnormal karyotype is observed. It is 46,XX in most cases and less frequently 46,XY. The major complication of this disease is gestational choriocarcinoma, a metastasizing tumor and a true allografted malignancy. This complication is infrequent in developed countries, but is more common in the developing countries and is then worsened by delayed care. The malignancies are often accompanied by acquired, possibly etiological genomic abnormalities. We investigated the presence of recurrent cytogenetic abnormalities in CHM and post-molar choriocarcinoma using metaphasic CGH (mCGH) and high-resolution 244K aCGH techniques. The 10 CHM studied by mCGH showed no chromosomal gains or losses. For post-molar choriocarcinoma, 11 tumors, whose diagnosis was verified by histopathology, were investigated by aCGH. Their androgenic nature and the absence of tumor DNA contamination by maternal DNA were verified by the analysis of microsatellite markers. Three choriocarcinoma cell lines (BeWo, JAR and JEG) were also analyzed by aCGH. The results allowed us to observe some chromosomal rearrangements in primary tumors, and more in the cell lines. Chromosomal abnormalities were confirmed by FISH and functional effect by immunohistochemical analysis of gene expression. Forty minimum critical regions (MCR) were defined on chromosomes. Candidate genes implicated in choriocarcinoma oncogenesis were selected. The presence in the MCR of many miRNA clusters whose expression is modulated by parental imprinting has been observed, for example in 14q32 or in 19q13.4. This suggests that, in gestational choriocarcinoma, the consequences of gene abnormalities directly linked to acquired chromosomal abnormalities are superimposed upon those of imprinted genes altered at fertilization.

Genome-wide high-resolution aCGH analysis of gestational choriocarcinomas.

Eleven samples of DNA from choriocarcinomas were studied by high resolution CGH-array 244 K. They were studied after histopathological confirmation of the diagnosis, of the androgenic etiology and after a microsatellite marker analysis confirming the absence of contamination of tumor DNA from maternal DNA. Three cell lines, BeWo, JAR, JEG were also studied by this high resolution pangenomic technique. According to aCGH analysis, the de novo choriocarcinomas exhibited simple chromosomal rearrangements or normal profiles. The cell lines showed various and complex chromosomal aberrations. 23 Minimal Critical Regions were defined that allowed us to list the genes that were potentially implicated. Among them, unusually high numbers of microRNA clusters and imprinted genes were observed.

NLRP7 and the genetics of post-molar choriocarcinomas in Senegal.

Gestational choriocarcinomas are malignant tumors of trophoblastic cells that affect 5-25% of women with sporadic hydatidiform moles (HMs) depending on countries and studies. Nucleotide binding and oligomerization domain-like receptor protein 7 (NLRP7) is a major gene responsible for recurrent HMs and recently mutations in this gene have also been shown in 13% of women with sporadic, non-recurrent  moles. To investigate the role of NLRP7 in the genetic susceptibility for the malignant degeneration of moles, we sequenced its 11 exons in 43 Senegalese patients with post-molar choriocarcinomas. We report the presence of three novel NLRP7 variants that were found only in patients but not in 100 controls from the Senegalese general population, 100 controls from the Tunisian general population, and 100 controls from the Canadian population. In addition, this analysis revealed significant differences in the frequencies of four non-synonymous NLRP7 variants between European and Senegalese controls with the biggest difference being for variant G487E present at a minor allele frequency of 3.5% in Europeans, 18.1% in Tunisians and 45.6% in Senegalese. Comparing human NLRP7 and its paralog, NLRP2, with their mammalian counterparts revealed that allele E at position 487 is most likely the ancestral allele that was acquired in Africa but driven to low frequencies in Europeans and Asians due to migration, population bottlenecks and selective pressures. This study is the first attempt to investigate the role of NLRP7 in choriocarcinomas and highlights the higher frequencies of NLRP7 variants in the general Senegalese and Tunisian populations both known to have higher frequencies of moles and choriocarcinomas.

NLRP7 in the spectrum of reproductive wastage: rare non-synonymous variants confer genetic susceptibility to recurrent reproductive wastage.

BACKGROUND: NLRP7 mutations are responsible for recurrent molar pregnancies and associated reproductive wastage. To investigate the role of NLRP7 in sporadic moles and other forms of reproductive wastage, the authors sequenced this gene in a cohort of 135 patients with at least one hydatidiform mole or three spontaneous abortions; 115 of these were new patients. METHODS/RESULTS: All mutations were reviewed and their number, nature and locations correlated with the reproductive outcomes of the patients and histopathology of their products of conception. The presence of NLRP7 mutations was demonstrated in two patients with recurrent spontaneous abortions, and some rare non-synonymous variants (NSVs), present in the general population, were found to be associated with recurrent reproductive wastage. These rare NSVs were shown to be associated with lower secretion of interleukin 1ß and tumour necrosis factor and therefore to have functional consequences similar to those seen in cells from patients with NLRP7 mutations. The authors also attempted to elucidate the cause of stillbirths observed in 13% of the patients with NLRP7 mutations by examining available placentas of the stillborn babies and live births from patients with mutations or rare NSVs. A number of severe to mild placental abnormalities were found, all of which are known risk factors for perinatal morbidity. CONCLUSIONS: The authors recommend close follow-up of patients with NLRP7 mutations and rare NSVs to prevent the death of the rare or reduced number of babies that reach term.

A novel approach identifies new differentially methylated regions (DMRs) associated with imprinted genes.

Imprinted genes are critical for normal human growth and neurodevelopment. They are characterized by differentially methylated regions (DMRs) of DNA that confer parent of origin-specific transcription. We developed a new strategy to identify imprinted gene-associated DMRs. Using genome-wide methylation profiling of sodium bisulfite modified DNA from normal human tissues of biparental origin, candidate DMRs were identified by selecting CpGs with methylation levels consistent with putative allelic differential methylation. In parallel, the methylation profiles of tissues of uniparental origin, i.e., paternally-derived androgenetic complete hydatidiform moles (AnCHMs), and maternally-derived mature cystic ovarian teratoma (MCT), were examined and then used to identify CpGs with parent of origin-specific DNA methylation. With this approach, we found known DMRs associated with imprinted genomic regions as well as new DMRs for known imprinted genes, NAP1L5 and ZNF597, and novel candidate imprinted genes. The paternally methylated DMR for one candidate, AXL, a receptor tyrosine kinase, was also validated in experiments with mouse embryos that demonstrated Axl was expressed preferentially from the maternal allele in a DNA methylation-dependent manner.

The primate-specific microRNA gene cluster (C19MC) is imprinted in the placenta.

Imprinted genes play crucial roles in mammalian development and disruption of their expression is associated with many human disorders including tumourigenesis; yet, the actual number of imprinted genes in the human genome remains a matter of debate. Here, we report on the unexpected finding that the chromosome 19 microRNA cluster (C19MC), the largest human microRNA gene cluster discovered so far, is regulated by genomic imprinting with only the paternally inherited allele being expressed in the placenta. DNA methylation profiling identified a differentially methylated region (C19MC-DMR1) that overlaps an upstream CpG-rich promoter region associated with short tandem repeats. It displays a maternal-specific methylation imprint acquired in oocytes and generates a complex population of large, compartimentalized non-coding RNA (ncRNA) species retained in close proximity to the C19MC transcription site. This occurs adjacent to, but not within, a poorly characterized nuclear Alu-rich domain. Interestingly, C19MC maps near another imprinted gene, the maternally expressed ZNF331 gene, and therefore may define a novel, previously unrecognized large imprinted primate-specific chromosomal domain. Altogether, our study adds C19MC to the growing list of imprinted repeated small RNA gene clusters and further strengthens the potential involvement of small ncRNAs in the function and/or the evolution of imprinted gene networks.

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.

Familial molar tissues due to mutations in the inflammatory gene, NALP7, have normal postzygotic DNA methylation.

An imprinting disorder has been believed to underlie the etiology of familial biparental hydatidiform moles (HMs) based on the abnormal methylation or expression of imprinted genes in molar tissues. However, the extent of the epigenetic defect in these tissues and the developmental stage at which the disorder begins have been poorly defined. In this study, we assessed the extent of abnormal DNA methylation in two HMs caused by mutations in the recently identified 19q13.4 gene, NALP7. We demonstrate normal postzygotic DNA methylation patterns at major repetitive and long interspersed nuclear elements (LINEs), genes on the inactive X-chromosome, three-cancer related genes, and CpG rich regions surrounding the PEG3 differentially methylated region (DMR). Our data provide a comprehensive assessment of DNA methylation in familial molar tissues and indicate that abnormal DNA methylation in these tissues is restricted to imprinted DMRs. The known role of NALP7 in apoptosis and inflammation pinpoints previously unrecognized pathways that could directly or indirectly underlie the abnormal methylation of imprinted genes in molar tissues.

PRINS combined with indirect immunofluorescence.

Primed in situ labeling (PRINS) has proven to be an attractive alternative to fluorescence in situ hybridization for in situ DNA labeling and for being combined on the same slide with others methods. For the aim of a study on the asymmetrical segregation of the chromosomes of the megakaryocytes during polyploidization, we developed a simultaneous PRINS and immunofluorescent labeling. We report here the method, which enabled us to visualize the centromere of selected chromosomes and the achromatic spindle on the same picture, a method that may be of a more general application.

Integration of Myeloblastosis Associated Virus proviral sequences occurs in the vicinity of genes encoding signaling proteins and regulators of cell proliferation.

AIMS: Myeloblastosis Associated Virus type 1 (N) [MAV 1(N)] induces specifically nephroblastomas in 8-10 weeks when injected to newborn chicken. The MAV-induced nephroblastomas constitute a unique animal model of the pediatric Wilms' tumor. We have made use of three independent nephroblastomas that represent increasing tumor grades, to identify the host DNA regions in which MAV proviral sequences were integrated. METHODS: Cellular sequences localized next to MAV-integration sites in the tumor DNAs were used to screen a Bacterial Artificial Chromosomes (BACs) library and isolate BACs containing about 150 kilobases of normal DNA corresponding to MAV integration regions (MIRs). These BACs were mapped on the chicken chromosomes by Fluorescent In Situ Hybridization (FISH) and used for molecular studies. RESULTS: The different MAV integration sites that were conserved after tumor cell selection identify genes involved in the control of cell signaling and proliferation. Syntenic fragments in human DNA contain genes whose products have been involved in normal and pathological kidney development, and several oncogenes responsible for tumorigenesis in human. CONCLUSION: The identification of putative target genes for MAV provides important clues for the understanding of the MAV pathogenic potential. These studies identified ADAMTS1 as a gene upregulated in MAV-induced nephroblastoma and established that ccn3/nov is not a preferential site of integration for MAV as previously thought. The present results support our hypothesis that the highly efficient and specific MAV-induced tumorigenesis results from the alteration of multiple target genes in differentiating blastemal cells, some of which are required for the progression to highly aggressive stages. This study reinforces our previous conclusions that the MAV-induced nephroblastoma constitutes an excellent model in which to characterize new potential oncogenes and tumor suppressors involved in the establishment and maintenance of tumors.

Cytogenetic repartition of chicken CR1 sequences evidenced by PRINS in Galliformes and some other birds.

Chicken repeat 1 (CR1) belongs to the non-long repeat class of retrotransposons. Nearly 100000 repeats interspersed in the chicken genome are subdivided into at least six distinct subfamilies, each 300 bp long and all sharing substantial sequence similarity. CR1-like elements were found in genomes from invertebrates to mammals, suggesting their importance for genome structure and/or function. Moreover, numerous data support the hypothesis of their implication in regulation of gene expression. So, the chromosomal distribution of these CR1 sequences in vertebrates is of great interest to improve our knowledge about the genome structure, function and evolution. A comparison of the cytogenetic distribution of CR1 sequences was performed by PRINS using consensus chicken primers on the chromosomes of chicken and species of several bird orders: Galliformes, Anseriformes, Passeriformes and Falconiformes. The study revealed that CR1 repeats are spread over nearly all chicken chromosomes with a higher density on the macrochromosomes and in particular with hot spots on subtelomeric regions of chromosome 1, 2, 3q, 4q, 5q. Their distribution on the macrochromosomes forms a kind of banding pattern, which was not systematically matched with R- or G-banding. This banding pattern appears to be conserved on the chromosomes of the Galliformes studied, irrespective of their karyotypes, rearranged or not. CR1 primers also show similar signals on the chromosomes of birds phylogenetically more distant (Anseriformes, Passeriformes and Falconiformes). This fact confirms the importance of these sequences at the large scale of bird evolution and in the chromosomal structure. The location of CR1 sequences, and in particular of the hot spots, mainly within the richest CG areas are in conformity with the data on an epigenetic role of these highly conserved sequences.

Characterization of quantitative chromosomal abnormalities in renal cell carcinomas by interphase four-color fluorescence in situ hybridization.

Renal cell carcinomas (RCC) in adults are histologically heterogeneous solid tumors with specific chromosomal abnormality patterns included in the World Health Organization (WHO) classification. To overcome some of the drawbacks of cytogenetic and comparative genomic hybridization (CGH) analyses, we designed a first-generation cytogenetic diagnostic test using four-color fluorescence in situ hybridization (FISH) on interphase nuclei. We selected 51 bacterial artificial chromosome and P1-derived artificial chromosome clones covering 17 chromosomal regions involved in the abnormalities of the adult RCC histologic subtypes. An initial set of probes allowed the identification of clear-cell RCC, papillary RCC, and other RCC on a single slide. A second test allowed the detection of additional chromosomal abnormalities or aberrations specific to chromophobic RCC and oncocytomas. We tested 25 cases of RCC, and the results were in agreement with those of cytogenetic techniques and/or CGH methods. The techniques appeared to be very sensitive, because small tumoral cell clones that were undetected by other cytogenetic methods were identified with this method. It was concluded that the multicolor FISH test was specific and sensitive, easy to perform, and could be part of the investigation process in RCC.

PTEN and DMBT1 homozygous deletion and expression in medulloblastomas and supratentorial primitive neuroectodermal tumors.

Medulloblastoma, which accounts for 20-25% of all childhood brain tumors, is defined as a primitive neuroectodermal tumor (PNET) located in the cerebellum. Supratentorial PNET are less frequent than medulloblastoma. But their clinical outcome is worse than in medulloblastomas. Chromosome 10q contains at least 2 tumor suppressor genes that might play a role in brain tumor development: PTEN and DMBT1. The aim of this study was to compare the status of homozygous deletion and expression of PTEN and DMBT1 genes in PNET primary tumor samples and cell lines. Homozygous deletions of PTEN and DMBT1 were studied in 32 paraffin-embedded PNET samples (23 medulloblastomas and 9 supratentorial PNET) and in 7 PNET cell lines, by differential PCR and by FISH. PTEN homozygous losses were demonstrated in 7 medulloblastomas (32%) and in no supratentorial PNET, while homozygous deletions of DMBT1 appeared in 1 supratentorial PNET (20%) and in 7 medulloblastomas (33%). No homozygous deletion of PTEN or DMBT1 was detected in any of the PNET cell lines either by differential PCR or by FISH. Expression study of the 2 genes was performed in the 7 PNET cell lines by RT-PCR. One PNET cell line lacked PTEN and DMBT1 expression, while 2 medulloblastoma cell lines did not express DMBT1. Our results add some positive data to the hypothesis that supratentorial PNETs and medulloblastomas might be genetically different.

[From the conception of the PRINS to its coronation]. / De la conception du PRINS à son couronnement.

As a non-isotopic molecular cytogenetic technique, the primed in situ (PRINS) labelling reaction represents a major technological progress achieved in the past decade. It has become a routine technique for the microscopic visualization of specific DNA sequences in cells and nuclei and constitutes a good alternative to the fluorescence in situ hybridization (FISH) procedure. Among the multiple advantages that characterize the PRINS technique, specificity, rapidity, reliability, reproducibility, and cost-effectiveness can be mentioned. PRINS can be in addition associated with other techniques like FISH, indirect immunofluorescence, and nick translation. The most recent developments show the great potential of this technique. Now PRINS can be used to study single-copy genes and, consequently, can be routinely used to investigate deletions associated with microdeletion syndromes. Therefore, the PRINS technique has the potential to become a widely used molecular cytogenetic tool in clinics and research. This short review presents how the PRINS technique contributed to further the understanding of biological phenomena and describes the different possibilities and applications of the PRINS method in several biological and clinical fields (pre-implantation testing, prenatal, constitutional and oncologic genetic diagnosis).

Multiple excitation confocal analysis of targets in nuclei of cytogenetic preparations.

OBJECTIVE: To demonstrate that cellular preparations requiring color analysis of different domains stained by molecular cytogenetic methods (fluorescence in situ hybridization) can be processed by spectral analysis of fluorescent emissions by either factor analysis of medical image sequences (FAMIS) or a META confocal configuration to isolate fluorescent probes. STUDY DESIGN: Three-dimensional sequences of images obtained by spectral analysis in a META confocal microscope (Carl Zeiss SAS, Jena, Germany) were analyzed by META processing and the FAMIS algorithm, which provides factor curves. META and factor images were then the result of image-processing methods that cover emission spectra. RESULTS: Factor curves and factor or META images can help to analyze targets inside nuclei. CONCLUSION: It is possible to process preparations containing numerous spots on different colors to differentiate stained targets and to improve visualization and detection.

Characterization of the atypical karyotype of the black-winged kite Elanus caeruleus (Falconiformes: Accipitridae) by means of classical and molecular cytogenetic techniques.

The karyotype of the black-winged kite (Elanus caeruleus), a small diurnal raptor living in Africa, Asia and southern Europe, was studied with classical (G-, C-, R-banding, and Ag-NOR staining) and molecular cytogenetic methods, including primed in-situ labelling (PRINS) and fluorescence in-situ hybridization (FISH) with telomeric (TTAGGG) and centromeric DNA repeats. The study revealed that the genome size, measured by flow cytometry (3.1 pg), is in the normal avian range. However, the black-winged kite karyotype is particularly unusual among birds in having a moderate diploid number of 68 chromosomes, and containing only one pair of dot-shaped microchromosomes. Moreover, the macrochromosomes are medium-sized, with the Z and W gonosomes being clearly the largest in the set. C-banding shows that constitutive heterochromatin is located at the centromeric regions of all chromosomes, and that two pairs of small acrocentrics and the pair of microchromosomes are almost entirely heterochromatic and G-band negative. The distribution pattern of a centromeric repeated DNA sequence, as demonstrated by PRINS, follows that of C-heterochromatin. The localization of telomeric sequences by FISH and PRINS reveals many strong telomeric signals but no extratelomeric signal was observed. The atypical organization of the karyotype of the black-winged kite is considered in the context of the modes of karyotypic evolution in birds.

Maternal alleles acquiring paternal methylation patterns in biparental complete hydatidiform moles.

We previously mapped a maternal locus responsible for biparental complete hydatidiform moles (BiCHMs) to 19q13.4. The two index patients had a total of 14 molar pregnancies, eight abortions at various developmental stages, and one 16-year-old healthy offspring. We suggested that the defective gene deregulates the expression of imprinted genes. Here, we report the methylation status of four imprinted genes in two BiCHMs from the two sisters, the 16-year-old normal offspring, and two sporadic BiCHMs from unrelated patients. Using two bisulfite-based methods, we demonstrate a general trend of abnormal hypomethylation at the paternally expressed genes, PEG3 and SNRPN, and hypermethylation at the maternally expressed genes, NESP55 and H19, in two to four BiCHMs. Using single nucleotide polymorphisms, we provide the first evidence that SNRPN, NESP55 and H19 are abnormally methylated on the maternal alleles in BiCHMs. We show, in the BiCHMs from the two sisters, that the abnormally methylated H19 allele is inherited from either the maternal grandmother or the maternal grandfather. These data suggest that the abnormal methylation in BiCHMs is not due to an error in erasing the parental imprinting marks but rather in the re-establishment of the new maternal marks during oogenesis or their postzygotic maintenance. The defective 19q13.4 locus may have led to the development of variable degrees of 'faulty' paternal marks on the maternal chromosomes.