Post-zygotic origin of complete maternal chromosome 7 isodisomy and consequent loss of placental PEG1/MEST expression

Low-level mosaic trisomy 7 at amniocentesis in a pregnancy associated with cytogenetic discrepancy between cultured amniocytes and uncultured amniocytes, perinatal progressive decrease of the trisomy 7 cell line and a favorable fetal outcome

OBJECTIVE

We present low-level mosaic trisomy at amniocentesis in a pregnancy associated with cytogenetic discrepancy between cultured amniocytes and uncultured amniocytes, perinatal progressive decrease of the trisomy 7 cell line and a favorable fetal outcome.

CASE REPORT

A 40-year-old, primigravid woman underwent amniocentesis at 16 weeks of gestation because of advanced maternal age. Amniocentesis revealed a karyotype of 46,XY in cultured amniocytes. Simultaneous array comparative genomic hybridization (aCGH) analysis on the DNA extracted from uncultured amniocytes revealed the result of arr (7) × 2-3, (X,Y) × 1, consistent with 24% mosaicism for trisomy 7. Polymorphic DNA marker analysis on the DNA extracted from the uncultured amniocytes and parental bloods excluded uniparental disomy (UPD) 7. Prenatal ultrasound findings were normal. She was referred for genetic counseling at 19 weeks of gestation. No repeat amniocentesis was suggested, and continuing the pregnancy was advised. At 22 weeks of gestation, the result of soluble fms-like tyrosine kinase-1 (sFlt-1)/placental growth factor (PlGF) = 6.1 (normal < 38). She did not have preeclampsia. At 39 weeks of gestation, a 3346-g male baby was delivered without any phenotypic abnormality. aCGH analysis on the DNA extracted from cord blood and placenta revealed the result of arr (1-22) × 2, (X,Y) × 1 with no genomic imbalance in all tissues. When follow-up at age three months, the baby was normal in development and phenotype. The peripheral blood had a karyotype of 46,XY, and interphase fluorescence in situ hybridization (FISH) analysis using the bacterial artificial chromosome (BAC) probes of chromosome 7 showed disomy 7 cells in all 102/102 cells.

CONCLUSION

Low-level mosaic trisomy 7 at amniocentesis can be associated with cytogenetic discrepancy between cultured amniocytes and uncultured amniocytes, perinatal progressive decrease of the trisomy 7 cell line and a favorable fetal outcome.

Genetic counseling of non-invasive prenatal testing (NIPT) trisomy 7-positive pregnancies

Trisomy 7 is the most common observed type of rare autosomal trisomies (RATs) detected at expanded genome-wide non-invasive prenatal testing (NIPT). Genetic counseling of NIPT trisomy 7-positive pregnancies remains to be not easy because the parents may worry about the likelihood of adverse pregnancy outcomes, fetal abnormality and the necessity of invasive procedures for confirmation of fetal mosaic trisomy 7 and uniparental disomy (UPD) 7. This review provides a comprehensive information on the update issues concerning genetic counseling of NIPT trisomy 7-positive pregnancies.

Extensive Placental Methylation Profiling in Normal Pregnancies

The placental methylation pattern is crucial for the regulation of genes involved in trophoblast invasion and placental development, both key events for fetal growth. We investigated LINE-1 methylation and methylome profiling using a methylation EPIC array and the targeted methylation sequencing of 154 normal, full-term pregnancies, stratified by birth weight percentiles. LINE-1 methylation showed evidence of a more pronounced hypomethylation in small neonates compared with normal and large for gestational age. Genome-wide methylation, performed in two subsets of pregnancies, showed very similar methylation profiles among cord blood samples while placentae from different pregnancies appeared very variable. A unique methylation profile emerged in each placenta, which could represent the sum of adjustments that the placenta made during the pregnancy to preserve the epigenetic homeostasis of the fetus. Investigations into the 1000 most variable sites between cord blood and the placenta showed that promoters and gene bodies that are hypermethylated in the placenta are associated with blood-specific functions, whereas those that are hypomethylated belong mainly to pathways involved in cancer. These features support the functional analogies between a placenta and cancer. Our results, which provide a comprehensive analysis of DNA methylation profiling in the human placenta, suggest that its peculiar dynamicity can be relevant for understanding placental plasticity in response to the environment.

Mosaic UPD(7q)mat in a patient with silver Russell syndrome

BACKGROUND

Silver-Russell syndrome (SRS) is one of the imprinting disorders characterized by prenatal and postnatal growth restriction, relative macrocephaly, body asymmetry and characteristic facial features. ~ 10% of SRS cases are known to be associated with maternal uniparental disomy of chromosome 7 (UPD(7)mat). Mosaic maternal segmental UPD of 7q (UPD(7q)mat) is very rare, had only been described in one case before.

CASE PRESENTATION

We reported a second case of mosaic segmental UPD involving 7q. The patient presented with dysmorphic features including thin and short stature, triangular face, moderate protruding forehead, relative macrocephaly, fifth toe clinodactyly and irregular teeth, meeting the clinical diagnosed criteria of SRS. This case indicated that ~ 80% of mosaic UPD(7q)mat lead to the manifestation of main phenotypes of Silver-Russell syndrome.

CONCLUSIONS

Our case support the notion that there are genes control postnatal growth on long arm of chromosome 7 and indicate that ~ 80% of UPD(7q)mat mosaicism level was contributed to the SRS phenotype.

DNA methylation-associated repression of MEST/PEG1 expression contributes to the invasion of extravillous trophoblast cells

INTRODUCTION

The invasion of extravillous cytotrophoblasts (EVTs) into the maternal uterine decidua and vasculature is critical for human placenta development and pregnancy maintenance. The imprinted gene MEST/PEG1 has been implicated in trophoblast development; however, the role of MEST in EVT invasion and the accompanying early pregnancy complications are not fully understood.

METHODS

Western blot, immunofluorescence and immunohistochemistry were used to detect MEST protein expression and localization by using antibodies recognize 2 reported isoforms. Specific small interference RNA (siRNA) targeting both of the MEST isoforms was applied to silence MEST expression in extravillous explants and HTR8/SVneo cells. Cell invasion and migration were assessed using the Matrigel invasion, Transwell migration assay and the xCELLigence system. Promoter DNA methylation was examined using bisulfite-sequencing polymerase chain reaction (BSP).

RESULTS

MEST protein was highly expressed in EVTs in the first trimester placenta and in the invasive EVT cell lines HTR-8/Svneo and HPT-8. Weak MEST expression was found in cytotrophoblasts (CTBs) and the choriocarcinoma-derived CTB cell line JEG-3. The specific siRNA knockdown of MEST expression significantly reduced HTR-8/Svneo cell invasion and migration as well as extravillous explant outgrowth, which were associated with the downregulation of Twist, N-cadherin and Vimentin. Decreased MEST protein expression with isoform 2 promoter hypermethylation was observed in the placentas of missed abortions, suggesting a possible pathological mechanism of missed abortion.

CONCLUSIONS

Suppressed expression of MEST was associated with its isoform 2 promoter hypermethylation ex vivo placenta tissues and in vitro cultured EVT cell lines. The present results provide a possible pathological mechanism of missed abortion.

Chromosomal Mosaicism in Human Feto-Placental Development: Implications for Prenatal Diagnosis

Chromosomal mosaicism is one of the primary interpretative issues in prenatal diagnosis. In this review, the mechanisms underlying feto-placental chromosomal mosaicism are presented. Based on the substantial retrospective diagnostic experience with chorionic villi samples (CVS) of a prenatal diagnosis laboratory the following items are discussed: (i) The frequency of the different types of mosaicism (confined placental, CPM, and true fetal mosaicisms, TFM); (ii) The risk of fetal confirmation after the detection of a mosaic in CVS stratified by chromosome abnormality and placental tissue involvement; (iii) The frequency of uniparental disomy for imprinted chromosomes associated with CPM; (iv) The incidence of false-positive and false-negative results in CVS samples analyzed by only (semi-)direct preparation or long term culture; and (v) The implications of the presence of a feto-placental mosaicism for microarray analysis of CVS and non-invasive prenatal screening (NIPS).

Uniparental disomy and human disease: an overview

Uniparental disomy (UPD) refers to the situation in which both homologues of a chromosomal region/segment have originated from only one parent. This can involve the entire chromosome or only a small segment. As a consequence of UPD, or uniparental duplication/deficiency of part of a chromosome, there are two types of developmental risk: aberrant dosage of genes regulated by genomic imprinting and homozygosity of a recessive mutation. UPD models generated by reciprocal and Robertsonian translocation heterozygote intercrosses have been a powerful tool to investigate genomic imprinting in mice, whereas novel UPD patients such as those with cystic fibrosis and Prader-Willi syndrome, triggered the clarification of recessive diseases and genomic imprinting disorders in human. Newly developed genomic technologies as well as conventional microsatellite marker methods have been contributing to the functional and mechanistic investigation of UPD, leading to not only the acquisition of clinically valuable information, but also the further clarification of diverse genetic processes and disease pathogenesis.

Adiponectin expression in human fetal tissues during mid- and late gestation

Adiponectin (ApN), an adipocytokine expressed in adipocytes with antidiabetic and antiatherogenic actions, has been detected in cord blood, suggesting a putative role in intrauterine fetal development. The aim of this study was to confirm the presence of ApN in the fetal circulation and directly investigate ApN expression in fetal tissues. The study showed high ApN levels in umbilical venous blood from fetuses [n = 44; 31.2 +/- 14.1 (sd) mg/liter in umbilical vs. 8.4 +/- 4.0 in maternal circulation (P < 0.0001)] that positively correlated with gestational age. By using RT-PCR, Western blotting, and immunohistochemistry, ApN was detected in several fetal tissues at mid- and late gestation (from 14 to 36 wk) but not in the placenta. ApN was expressed in tissues of mesodermic origin, i.e. brown and white adipocytes, skeletal muscle fibers of diaphragm and iliopsoas, smooth muscle cells of small intestine and arterial walls, perineurium and renal capsule, and tissues of ectodermal origin, i.e. epidermis and ocular lens. The distribution of ApN expression in nonadipose tissues showed a general decline during the progression of gestation. The unexpected pattern of ApN expression in the human fetus may account for the high ApN levels in cord blood and predicts novel roles for ApN during fetal development.

Sex-specific chromosome instability in early human development

The predominance of females segregating chromosome aberrations to their offspring has been explained mostly by selection disadvantage of unbalanced products of spermatogenesis. However, analysis of data from the literature supports the idea that somatic cells of early female embryos are similar to female germ cells in that they are prone to malsegregation. The goal of this study was to compare the sex ratio (male to female ratio) of carriers of presumably mitotic-occurring chromosome abnormalities to identify any sex biases. In examining the literature, we found a female prevalence in cases of mosaicism associated with uniparental disomy (UPD) (26 male individuals/conceptions and 45 female individuals/conceptions, sex ratio is 0.58, significantly different from 1.06 in newborn population, P = 0.0292). This predominance was highest at gestational age <16 week (8 male and 22 female conceptuses, sex ratio is 0.36, significantly different from expected figure of 1.28, P = 0.0025), which diminished at later stages of fetal development indicating potential correction of trisomies predominantly in females. There is a threefold prevalence of 46,XX/45,X mosaics over 46,XY/45,X mosaics in prenatally diagnosed cases, which also suggests a gender-specific postzygotic chromosome loss. The male prevalence in Prader-Willi syndrome with maternal UPD of chromosome 15 also can be explained by sex-specific trisomy correction, with predominant loss of a maternal chromosome causing biparental inheritance and therefore, complete correction of trisomy in females (without UPD). Finally, there is a female predominance in carriers of chromosome rearrangement with pericentromere break (mosaicism for Robertsonian translocation/isochromosome, centric fission, nonacrocentric isochromosome, and whole arm rearrangement), in both prenatal (21 males and 36 females, sex ratio is 0.58, P < 0.0184) and postnatal ill-defined cases (14 males and 35 females, sex ratio is 0.40, P = 0.001). Thus, the findings presented in this paper suggest that, in addition to reduction in male fertility, and to probable selection against abnormal cell line(s), there are two mechanisms that contribute to female preponderance among carriers of mosaicism: sex-specific chromosome loss and sex-specific centromere instability. The data obtained suggest that females may have gonadal mosaicism for aneuploidies and structural rearrangements more often than males. This may lead to the maternal origin bias in offspring with trisomies or structural rearrangements.

Uniparental disomy (UPD) other than 15: Phenotypes and bibliography updated

Uniparental disomy (UPD) describes the inheritance of a pair of chromosomes from only one parent. The concept was introduced in Medical Genetics by Engel (1980); Am J Med Genet 6:137-143. Aside UPD 15, which is the most frequent one, up to now (February 2005) 197 cases with whole chromosome maternal UPD other than 15 (124 X heterodisomy, 59 X isodisomy, and 14 cases without information of the mode of UPD) and 68 cases with whole chromosome paternal UPD other than 15 (13 X heterdisomy, 53 X isodisomy, and 2 cases without information of the mode of UPD) have been reported. In this review we discuss briefly the problems associated with UPD and provide a comprehensive clinical summary with a bibliography for each UPD other than 15 as a guide for genetic counseling.

Fetal and placental chromosomal mosaicism revealed by QF-PCR in severe IUGR pregnancies

A number of genetic and environmental factors are taken into account as responsible for intrauterine growth restriction (IUGR); nevertheless, the relevance of genetic alteration in IUGR aetiology remains to be determined. The aim of this study was to investigate using a combined cytogenetic-molecular approach, improved by a new application of QF-PCR method, the presence of mosaic chromosomal changes in fetal/placental samples from 12 pregnancies with unexplained severe IUGR. This multiple approach allowed us to reveal and quantify subtle chromosomal mosaicisms with less than 5% of trisomic cells even in cases in which cytogenetic and FISH analyses failed to reveal them. These are three pregnancies with a mosaic trisomy for chromosomes 7, 2 and 14; the former case presented matUPD7 and was previously described in this journal (Placenta 22 (2001) 813) in association with pre- and postnatal growth restriction. It is intriguing that chromosomes 7, 2 and 14 are known or suspected to harbour imprinted genes, so that an unbalanced gene dosage in a subset of cells during embryonic development could lead to an early impairment of placental function. Our findings indicate that extensive molecular and cytogenetic studies of IUGR fetal and placental tissues are necessary to reveal at least part of the heterogeneous genetic lesions implicated in IUGR phenotypes.

The role of imprinted genes in fetal growth

Genomic imprinting is the phenomenon by which one of the two alleles of a subset of genes is preferentially expressed according to its parental origin. This pattern of inheritance is different from the more frequent mode of Mendelian inheritance, which is not influenced by the parental origin of the allele. The idea that imprinted genes can affect fetal growth is becoming increasingly intriguing as it has been shown that most imprinted genes are expressed in the placenta and some play a role in regulating the interactions between its fetal and maternal interfaces. This article considers genomic imprinting by reviewing recent findings of alterations in fetal growth related to different types of genetic changes affecting the expression of imprinted genes. Among the genetic anomalies, the uniparental disomy (UPD) defines the inheritance of both homologous chromosomes from only one parent. UPDs of a number of chromosomes have been described in association with effects on the phenotype. We reviewed cases of UPD reported till now with particular reference to those associated to growth alterations.