Reevaluating confined placental mosaicism

PGT-A mosaicism based on NGS intermediate copy numbers: is it time to stop reporting them?

Mosaicism represents a genuine real phenomenon, but its high prevalence and undisclosed clinical significance, stress the burden on genetic counseling and the management of PGT-A results. Even though the assumption of mosaicism from NGS intermediate chromosome copy number profiles may represent a reasonable interpretation, other potential technical reasons, including amplification bias, contamination, biopsy technique, or the analysis algorithms, may constitute alternative explanations. Thresholds confining mosaicism ranges are established according to models employing mixtures of normal and abnormal cells with steady conditions of quantity and quality which are unable to reflect the full extent of variability present in a trophectoderm (TE) biopsy specimen. When the concordance of TE with the ICM is considered, mosaic TE biopsies poorly correlate with the chromosomal status of the remaining embryo, displaying mostly ICM aneuploidy in cases of TE high-range mosaics diagnosis and euploidy when mosaicism grade in TE is less than 50% (low-mid range mosaicism), which implies an evident overestimation of mosaicism results. Indeed, a binary classification of NGS profiles that excludes mosaic ranges, including only euploid and aneuploid diagnosis, provides higher specificity and accuracy in identifying abnormal embryos and discarding them. As intermediate copy number profiles do not represent strong evidence of mosaicism but only an inaccurate and misleading assumption, and considering that no increased risk has been reported in the offspring, until diagnosis specificity is improved and its clinical implications are determined, laboratories should consider limiting predictions to euploid and aneuploid and stop reporting mosaicism.

Update on preimplantation genetic testing for aneuploidy and outcomes of embryos with mosaic results

Preimplantation genetic testing for aneuploidy (PGT-A) is used as a frequent add-on for in-vitro fertilization (IVF) to improve clinical outcomes. The purpose is to select a euploid embryo following chromosomal testing on embryo biopsies. The current practice includes comprehensive chromosome screening (CCS) technology applied on trophectoderm (TE) biopsies. Despite its widespread use, PGT-A remains a controversial topic mainly because all of the RCTs comprised only good prognosis patients with 2 or more blastocysts available; hence the results are not generalizable to all groups of patients. Furthermore, with the introduction of the highly-sensitive platforms into clinical practice (i.e. next-generation sequencing [NGS]), a result consistent with intermediate copy number surfaced and is termed "Mosaic," consistent with a mixture of euploid and aneuploid cells within the biopsy sample. The optimal disposition and management of embryos with mosaic results is still an open question, as many 'mosaics' generated healthy live births with no identifiable congenital anomalies. The present article provides a complete and comprehensive up-to-date review on PGT-A. It discusses in detail the findings of all the published RCTs on PGT-A with CCS, comments on the subject of "mosaicism" and its current management, and describes the latest technique of non-invasive PGT-A.

Pregnancy outcome of confined placental mosaicism: meta-analysis of cohort studies

OBJECTIVE

This study aimed to assess the rate of adverse obstetrical and neonatal outcomes in pregnancies diagnosed with confined placental mosaicism relative to that of unaffected controls.

DATA SOURCES

Web-based databases were searched using relevant key words, and articles published from 1980 to February 2022 were retrieved.

STUDY ELIGIBILITY CRITERIA

Observational studies in English language including ≥10 cases of singleton pregnancies with diagnosis of confined placental mosaicism were included. The diagnosis was established after detection of any chromosomal abnormality at chorionic villus sampling for any indication, followed by normal karyotype from amniotic fluid or neonatal leukocyte culture.

METHODS

Two authors independently screened the references for eligibility, data extraction, and assessment of methodological quality using the Newcastle-Ottawa scale. All available obstetrical and neonatal outcomes were recorded. Random-effect meta-analysis was performed to estimate pooled odds ratios and 95% confidence intervals of available outcomes in pregnancies with and without confined placental mosaicism. Statistical heterogeneity was evaluated with I2 statistics (International Prospective Register of Systematic Reviews registration number: CRD42021260319).

RESULTS

Of the 80 articles reviewed, 8 retrospective matched-cohort studies (708 cases of confined placental mosaicism and 11,599 unaffected controls) compared cases with and without confined placental mosaicism and were included in the meta-analysis. The risk of delivering small-for-gestational-age neonates was significantly increased in confined placental mosaicism pregnancies according to crude analysis (odds ratio, 2.45; 95% confidence interval, 1.23-4.89; I2=72%) and to sensitivity analysis of high-quality studies (odds ratio, 3.65; 95% confidence interval, 2.43-5.57; I2=0%). Similarly, confined placental mosaicism resulted in an increased risk of birthweight below the third centile (odds ratio, 5.33; 95% confidence interval, 1.19-24.19; I2= 83%). Subgroup analysis revealed that the risk of delivering small-for-gestational-age neonates was 3-fold higher for confined placental mosaicism excluding trisomy 16, and 11-fold higher for cases including trisomy 16 only vs unaffected controls, respectively. No difference was found in the risk of low birthweight and preterm birth (at <37 weeks' gestation). Other outcomes were insufficiently reported, therefore they were not analyzed.

CONCLUSION

Pregnant women prenatally diagnosed with confined placental mosaicism have an increased risk of impaired fetal growth, suggesting the need for intensified antenatal surveillance.

Ethical Aspects of Prenatal DNA Testing

Cell-free DNA (cfDNA) first-trimester screening for fetal aneuploidies, as a non-invasive, safe, and rather accurate method, has changed prenatal screening policies all over the world. Owing to aggressive marketing, cfDNA screening tests exhibit global popularity and a rapid spread in routine prenatal care. However, wide availability of the tests, together with observed difficulties in the test’s interpretation, bring to light several serious ethical concerns. To date it is vital to identify and address the most important ethical, legal, and social issues regarding prenatal screening tests. Furthermore, guidelines and restrictions in certain cfDNA screening advancements that may provide information regarding fetal genetic traits of unknown clinical significance, conditions with variable penetrance, or late-onset conditions, should be considered.

Evidence-based clinical prioritization of embryos with mosaic results: a systematic review and meta-analysis

PURPOSE

The purpose of this review and meta-analysis is to standardize the practice of mosaic embryo transfer, based on the current available evidence.

METHODS

This is a systematic review and meta-analysis. Relevant studies published were comprehensively selected using PubMed, Medline, Embase, and CENTRAL until 5 March 2021. Prospective and retrospective studies reporting the genetic analysis and clinical outcomes of mosaic embryo transfer were included. Risk of bias assessment was based on the Newcastle-Ottawa scale for the non-randomized studies. The primary and secondary outcomes were combined ongoing pregnancy and live birth rate and miscarriage rate, respectively.

RESULTS

There were no differences between low and high mosaic embryos when a cut-off of 40% was used in terms of OP/LBR and SAB. However, low mosaics with a cut-off of 50% compared to high mosaics showed a significantly higher OP/LBR in the NGS but not in the a-CGH group, and a significantly lower risk of SAB. No differences were noted between mosaic monosomies versus trisomies and single versus double mosaics for both OP/LBR and SAB. Finally, segmental mosaics showed a higher OP/LBR and a lower SAB compared to whole chromosomes, and single and double mosaics had a higher OP/LBR compared to complex mosaics.

CONCLUSIONS

A cut-off of 50% in defining low versus high mosaic embryos is preferable to a threshold of 40% when using NGS platform. No priority was established for mosaic trisomies over monosomies. Single and double mosaics must be preferred over complex mosaics and segmental mosaics must be preferred over whole chromosome mosaics. These results should be interpreted in the context of specific chromosomes involved in the mosaicism.

The outcome of human mosaic aneuploid blastocysts after intrauterine transfer: A retrospective study

To explore whether mosaic/aneuploid embryos can be transferred when there is no normal embryo available for transplant.The clinical pregnancy outcomes and amniocentesis outcomes of transplanted mosaic embryos during 28 preimplantation genetic testing (PGT) cycles were retrospectively analyzed. Chromosomes of 4 donated mosaic blastocysts were comprehensively screened by next-generation sequencing.About 10 (35.7%) of the 28 transferred mosaic embryos were implanted and had a gestational sac. But 5 women miscarried due to lack of fetal heartbeat between the 7th and 12th week of pregnancy. Five women had full-term pregnancies and gave birth to 5 healthy babies. Three of the 4 donated mosaic blastocysts had normal trophectoderm and inner cell mass, but the other 1 had abnormal embryonic cell mass.When no normal transplantable embryo is available in the PGT cycles, but the underlying risk must be fully informed.

Prenatal Genetic Testing Options

All patients should be offered prenatal screening and diagnosis. Testing options depend on many factors, including patient age, family history, and patient preference. Options are rapidly changing with emerging technology. Aneuploidy screening options include ultrasound, maternal analytes, and cell-free DNA. Prenatal chromosomal microarray is the recommended diagnostic test for patients with anomalies visualized on prenatal ultrasound. Prenatal whole exome sequencing is clinically available but is limited by challenges with counseling, interpretation, and turn-around time. Future technologies are emerging and may soon allow for translation of prenatal diagnosis to in utero therapy.

Chromosomal microarray analysis on uncultured chorionic villus sampling can be complicated by confined placental mosaicism for aneuploidy and microdeletions

OBJECTIVE

This study aims to establish the incidence and implications of confined placental mosaicism (CPM) in the context of prenatal chromosomal microarray analysis (CMA).

METHODS

We retrospectively reviewed prenatal array data on 1382 consecutive chorionic villus sampling (CVS) specimens spanning the past 6 years, focusing on those for which whole CVS biopsy (both cytotrophoblast and mesenchymal cells) was used for CMA and cultured cells (primarily mesenchyme) was also analyzed or amniotic fluid (AF)/newborn blood was used for confirmation, to determine the frequency of mosaic abnormal findings that were the result of CPM.

RESULTS

Out of a total of 1382 consecutive CVS cases, we identified 42 (42/1382 = 3.0%) cases with abnormal array findings suggestive of mosaicism. Among them, 10 cases were unequivocally interpreted as CPM based on a normal AF/newborn blood confirmatory result. In addition, another 10 cases were interpreted as provisional CPM based on normal results on cultured cells. Notably, 40% (8/20) of the cases revealed complex findings, including multiple mosaic aneuploidies, mosaic submicroscopic copy number variation (CNV), and mosaic aneuploidy plus mosaic CNV.

CONCLUSION

Abnormal CMA results from CVS specimens should be interpreted with caution when mosaicism is evident or suspected. Furthermore, confirmatory testing on amniotic fluid, which contains cells derived from the fetus, is recommended in these cases.

A Paradigm Shift: Considerations in Prenatal Cell-Free DNA Screening

BACKGROUND

Testing to determine the health of a fetus has undergone multiple iterations since the widespread adoption of amniocentesis in the 1970s, including several combinations of ultrasound and/or maternal serum screening. The clinical paradigm for prenatal screening for fetal chromosome aneuploidies was transformed by the introduction of cell-free DNA (cfDNA) screening or noninvasive prenatal screening in 2011.

CONTENT

The clinical performance of cfDNA screening is well-established for the most common autosomal and sex chromosome aneuploidies with a detection rate exceeding 90% for all aneuploidies. One of the most significant advantages of cfDNA screening relative to maternal serum screening is the markedly reduced false-positive rate, which is <0.5%. The clinical implementation of cfDNA screening is discussed at length, including key biological, preanalytical, and analytical factors that affect test performance.

SUMMARY

cfDNA prenatal screening for whole chromosome aneuploidies has become routine in high-risk obstetric populations. There is tremendous interest in expanding cfDNA screening to the general obstetric population. Early studies suggest that routine application of cfDNA screening is both feasible and effective, although significant economic and quality control considerations remain.

Quantitative fluorescent polymerase chain reaction for rapid prenatal diagnosis of fetal aneuploidies in chorionic villus sampling in a single institution

Objective

To validate quantitative fluorescent polymerase chain reaction (QF-PCR) via chorionic villus sampling (CVS) for the diagnosis of fetal aneuploidies.

Methods

We retrospectively reviewed the medical records of consecutive pregnant women who had undergone CVS at Cheil General Hospital between December 2009 and June 2014. Only cases with reported QF-PCR before long-term culture (LTC) for conventional cytogenetic analysis were included, and the results of these two methods were compared.

Results

A total of 383 pregnant women underwent QF-PCR and LTC via CVS during the study period and 403 CVS specimens were collected. The indications of CVS were as follows: abnormal first-trimester ultrasonographic findings, including increased fetal nuchal translucency (85.1%), advanced maternal age (6.8%), previous history of fetal anomalies (4.2%), and positive dual test results for trisomy 21 (3.9%). The results of QF-PCR via CVS were as follows: 76 (18.9%) cases were identified as trisomy 21 (36 cases), 18 (33 cases), or 13 (seven cases), and 4 (1.0%) cases were suspected to be mosaicism. All results of common autosomal trisomies by QF-PCR were consistent with those of LTC and there were no false-positive findings. Four cases suspected as mosaicism in QF-PCR were confirmed as non-mosaic trisomies of trisomy 21 (one case) or trisomy 18 (three cases) in LTC.

Conclusion

QF-PCR via CVS has the advantage of rapid prenatal screening at an earlier stage of pregnancy for common chromosomal trisomies and thus can reduce the anxiety of parents. In particular, it can be helpful for pregnant women with increased fetal nuchal translucency or abnormal first-trimester ultrasonographic findings.

Physiological Aspects of Female Fertility: Role of the Environment, Modern Lifestyle, and Genetics

Across the Western World there is an increasing trend to postpone childbearing. Consequently, the negative influence of age on oocyte quality may lead to a difficulty in conceiving for many couples. Furthermore, lifestyle factors may exacerbate a couple's difficulty in conceiving due mainly to the metabolic influence of obesity; however, the negative impacts of low peripheral body fat, excessive exercise, the increasing prevalence of sexually transmitted diseases, and smoking all have significant negative effects on fertility. Other factors that impede conception are the perceived increasing prevalence of the polycystic ovary syndrome, which is further exacerbated by obesity, and the presence of uterine fibroids and endometriosis (a progressive pelvic inflammatory disorder) which are more prevalent in older women. A tendency for an earlier sexual debut and to have more sexual partners has led to an increase in sexually transmitted diseases. In addition, there are several genetic influences that may limit the number of oocytes within the ovary; consequently, by postponing attempts at childbearing, a limitation of oocyte number may become evident, whereas in previous generations with earlier conception this potentially reduced reproductive life span did not manifest in infertility. Environmental influences on reproduction are under increasing scrutiny. Although firm evidence is lacking however, dioxin exposure may be linked to endometriosis, phthalate exposure may influence ovarian reserve, and bisphenol A may interfere with oocyte development and maturation. However, chemotherapy or radiotherapy is recognized to lead to ovarian damage and predispose the woman to ovarian failure.

Could Digital PCR Be an Alternative as a Non-Invasive Prenatal Test for Trisomy 21: A Proof of Concept Study

Objective

NIPT for fetal aneuploidy by digital PCR has been hampered by the large number of PCR reactions needed to meet statistical requirements, preventing clinical application. Here, we designed an octoplex droplet digital PCR (ddPCR) assay which allows increasing the number of available targets and thus overcomes statistical obstacles.

Method

After technical optimization of the multiplex PCR on mixtures of trisomic and euploid DNA, we performed a validation study on samples of plasma DNA from 213 pregnant women. Molecular counting of circulating cell-free DNA was performed using a mix of hydrolysis probes targeting chromosome 21 and a reference chromosome.

Results

The results of our validation experiments showed that ddPCR detected trisomy 21 even when the sample’s trisomic DNA content is as low as 5%. In a validation study of plasma samples from 213 pregnant women, ddPCR discriminated clearly between the trisomy 21 and the euploidy groups.

Conclusion

Our results demonstrate that digital PCR can meet the requirements for non-invasive prenatal testing of trisomy 21. This approach is technically simple, relatively cheap, easy to implement in a diagnostic setting and compatible with ethical concerns regarding access to nucleotide sequence information. These advantages make it a potential technique of choice for population-wide screening for trisomy 21 in pregnant women.

Non-invasive prenatal testing for fetal chromosome abnormalities: review of clinical and ethical issues

Genomics-based non-invasive prenatal screening using cell-free DNA (cfDNA screening) was proposed to reduce the number of invasive procedures in current prenatal diagnosis for fetal aneuploidies. We review here the clinical and ethical issues of cfDNA screening. To date, it is not clear how cfDNA screening is going to impact the performances of clinical prenatal diagnosis and how it could be incorporated in real life. The direct marketing to users may have facilitated the early introduction of cfDNA screening into clinical practice despite limited evidence-based independent research data supporting this rapid shift. There is a need to address the most important ethical, legal, and social issues before its implementation in a mass setting. Its introduction might worsen current tendencies to neglect the reproductive autonomy of pregnant women.

Comparison of pre-procedural anxiety and depression scores for patients undergoing chorion villus sampling and amniocentesis: An alternative perspective on prenatal invasive techniques

OBJECTIVE

To compare the pre-procedural anxiety and depression levels of patients undergoing chorion villus sampling (CVS) and amniocentesis (AC).

METHODS

Patients referred to our department for fetal karyotype analysis with a positive first or second trimester screening test for aneuploidy between January 2013 to June 2015 were included. CVS and AC procedures were performed in patients with gestation periods of between 11-14 and 16-20 weeks, respectively. Anxiety was evaluated using the Spielberger State-Trait Anxiety Inventory (STAI), and depression was assessed using the Beck Depression Inventory II (BDI-II).

RESULTS

A total of 1,400 patients were included. Compared to first trimester controls, patients undergoing CVS had significantly higher STAI-state and BDI-II results. Likewise, patients undergoing AC had higher STAI-state and BDI-II scores than controls in the second trimester. In terms of STAI-trait results, no difference was found between the groups. Our results also showed that, compared to AC group, patients undergoing CVS had similar STAI-state, STAI-trait and but higher BDI-II scores.

CONCLUSION

We conclude that evaluating the stress and depression levels of these patients should be one of the routine procedures in pregnancy follow-up.

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).

A 26-Year Experience in Chorionic Villus Sampling Prenatal Genetic Diagnosis

This report describes the trends of chorionic villus sampling (CVS) referred for prenatal genetic diagnosis in the past two and a half decades in a Portuguese Center. Our cohort of 491 CVS was mostly performed by the transcervical method at the 12th gestational week. Data collected within the framework of this study relate to the following: sampling method, referral reason versus abnormality and incidence of procedure-related pregnancy loss, that declined to about 0.5% over the last 15 years. The year 2000 represented a change in referral reasons for chorionic tissue collection, shifting from almost exclusively for cytogenetic testing to an increasing number of molecular tests for monogenic disorders. Herein, success rates as well as cytogenetic and/or molecular DNA results are presented. These latter include not only tests for several monogenic disorders, but also aneuploidy and maternal cell contamination screening. This retrospective analysis reiterates that CVS is a safe and reliable first trimester technique for prenatal diagnosis in high genetic risk pregnancies.

Cytogenetic follow-up of chromosomal mosaicism detected in first-trimester prenatal diagnosis

OBJECTIVE

To contribute to the risk assessment of true fetal mosaicism after detection of a mosaic chromosomal anomaly in chorionic villus samples (CVS) in order to enable more effective counseling and pregnancy management.

METHODS

We retrospectively reviewed 7112 consecutive CVS analyzed on both direct preparations and cultured cells. In 135 out of the 177 cases of mosaicism, we performed cytogenetic follow-up and determined the frequency of confined placental mosaicism (CPM) and true fetal mosaicism according to type and distribution of the cytogenetic abnormality.

RESULTS

True fetal mosaicism was detected in 38 out of 135 cases (28.15%), confirming the higher incidence of CPM (71.85%). Confirmation rate of CV mosaicism depends on the combination of placental cell lineages affected, chromosome involved and mosaic versus non-mosaic chromosomal anomaly. The overall probability of fetal involvement significantly rises with involvement of mesenchymal cells: 5.88% abnormal cytotrophoblast, 20.96% abnormal mesenchyme and 58.97% anomalies in both tissues.

CONCLUSION

Most of the mosaic findings at CVS are unreliable indicators of the fetal karyotype. Our study contributes to large series with cytogenetic information from the different tissues along the cytotrophoblast-extraembrional mesoderm-fetus axis in order to infer clinical relevance of the findings and to enable more effective genetic counseling.

The origin, mechanisms, incidence and clinical consequences of chromosomal mosaicism in humans

BACKGROUND

Chromosomal mosaicism, the presence of two or more distinct cell lines, is prevalent throughout human pre- and post-implantation development and can lead to genetic abnormalities, miscarriages, stillbirths or live births. Due to the prevalence and significance of mosaicism in the human species, it is important to understand the origins, mechanisms and incidence of mosaicism throughout development.

METHODS

Literature searches were conducted utilizing Pubmed, with emphasis on human pre- and post-implantation mosaicism.

RESULTS

Mosaicism persists in two separate forms: general and confined. General mosaicism is routine during human embryonic growth as detected by preimplantation genetic screening at either the cleavage or blastocyst stage, leading to mosaicism within both the placenta and fetus proper. Confined mosaicism has been reported in the brain, gonads and placenta, amongst other places. Mosaicism is derived from a variety of mechanisms including chromosome non-disjunction, anaphase lagging or endoreplication. Anaphase lagging has been implicated as the main process by which mosaicism arises in the preimplantation embryo. Furthermore, mosaicism can be caused by any one of numerous factors from paternal, maternal or exogenous factors such as culture media or possibly controlled ovarian hyperstimulation during in vitro fertilization (IVF). Mosaicism has been reported in as high as 70 and 90% of cleavage- and blastocyst-stage embryos derived from IVF, respectively.

CONCLUSIONS

The clinical consequences of mosaicism depend on which chromosome is involved, and when and where an error occurs. Mitotic rescue of a meiotic error or a very early mitotic error will typically lead to general mosaicism while a mitotic error at a specific cell lineage point typically leads to confined mosaicism. The clinical consequences of mosaicism are dependent on numerous aspects, with the consequences being unique for each event.

Noninvasive prenatal testing: limitations and unanswered questions

The clinical use of noninvasive prenatal testing to screen high-risk patients for fetal aneuploidy is becoming increasingly common. Initial studies have demonstrated high sensitivity and specificity, and there is hope that these tests will result in a reduction of invasive diagnostic procedures as well as their associated risks. Guidelines on the use of this testing in clinical practice have been published; however, data on actual test performance in a clinical setting are lacking, and there are no guidelines on quality control and assurance. The different noninvasive prenatal tests employ complex methodologies, which may be challenging for health-care providers to understand and utilize in counseling patients, particularly as the field continues to evolve. How these new tests should be integrated into current screening programs and their effect on health-care costs remain uncertain.

A rare case of a mosaic unbalanced translocation after chorionic villous sampling

BACKGROUND

Most of the literature suggests that unbalanced chromosomal translocations may lead to poor obstetrical outcomes. We present a case of an unbalanced translocation resulting in trisomy 1q and partial monosomy 20p identified on chorionic villous sampling (CVS).

METHOD

Case report with expert-derived clinical management and guidance.

RESULTS

After the abnormal CVS result, a subsequent amniocentesis revealed a normal 46,XX fetal karyotype. Detailed second trimester ultrasound of the fetus revealed no gross structural abnormalities. The CVS karyotype results were attributed to confined placental mosaicism (CPM) of the unbalanced translocation. The infant is 18 months old and has normal phenotype and karyotype.

CONCLUSION

We recommend that if CPM with an unbalanced translocation is diagnosed on CVS, parental karyotype and an amniocentesis should be offered in conjunction with genetic counseling. In rare instances, such as this one, an unbalanced translocation may have a favorable outcome.

Noninvasive fetal genome sequencing: a primer

We recently demonstrated whole genome sequencing of a human fetus using only parental DNA samples and plasma from the pregnant mother. This proof-of-concept study demonstrated how samples obtained noninvasively in the first or second trimester can be analyzed to yield a highly accurate and substantially complete genetic profile of the fetus, including both inherited and de novo variation. Here, we revisit our original study from a clinical standpoint, provide an overview of the scientific approach, and describe opportunities and challenges along the path toward clinical adoption of noninvasive fetal whole genome sequencing.

Confined placental mosaicism at chorionic villous sampling: risk factors and pregnancy outcome

OBJECTIVE

This study aims to investigate the clinical relevance of confined placental mosaicism (CPM) detected at chorionic villous sampling (CVS) and to identify risk factors for this condition.

METHOD

Women diagnosed with CPM between January 2005 and December 2009 were identified. They were matched to women with unremarkable CVS in a 1 : 2 ratio by study period and contacted by phone for interview.

RESULTS

One hundred fifteen exposed and 230 unexposed women were selected. Baseline characteristics did not differ between the study groups apart from maternal body mass index, which is mildly higher in the CPM group (+0.6 kg/m(2), p = 0.047), and maternal age, which is higher in women with type III CPM (39.7 ± 2.6 vs 37.1 ± 3.2 years, p = 0.005). A higher frequency of gestational hypertension was observed in exposed women (10% vs 2%) (p = 0.003). Small for gestational age newborns were more frequent in women with type I CPM (15% vs 5%, p = 0.03). The incidence of other main complications of pregnancy (stillbirth, prematurity, preeclampsia and gestational diabetes mellitus) was similar. Neonatal complications and subsequent infant health and development did not also differ.

CONCLUSION

Women with the diagnosis of CPM at CVS can be generally reassured regarding the course of pregnancy and infant health and development.

Is routine karyotyping required in prenatal samples with a molecular or metabolic referral?

As a routine, karyotyping of invasive prenatal samples is performed as an adjunct to referrals for DNA mutation detection and metabolic testing. We performed a retrospective study on 500 samples to assess the diagnostic value of this procedure. These samples included 454 (90.8%) chorionic villus (CV) and 46 (9.2%) amniocenteses specimens. For CV samples karyotyping was based on analyses of both short-term culture (STC) and long-term culture (LTC) cells. Overall, 19 (3.8%) abnormal karyotypes were denoted: four with a common aneuploidy (trisomy 21, 18 and 13), two with a sex chromosomal aneuploidy (Klinefelter syndrome), one with a sex chromosome mosaicism and twelve with various autosome mosaicisms. In four cases a second invasive test was performed because of an abnormal finding in the STC. Taken together, we conclude that STC and LTC karyotyping has resulted in a diagnostic yield of 19 (3.8%) abnormal cases, including 12 cases (2.4%) with an uncertain significance. From a diagnostic point of view, it is desirable to limit uncertain test results as secondary test findings. Therefore, we recommend a more targeted assay, such as e.g. QF-PCR, as a replacement of the STC and to provide parents the autonomy to choose between karyotyping and QF-PCR.

Somatic genome variations in health and disease

It is hard to imagine that all the cells of the human organism (about 10(14)) share identical genome. Moreover, the number of mitoses (about 10(16)) required for the organism's development and maturation during ontogeny suggests that at least a proportion of them could be abnormal leading, thereby, to large-scale genomic alterations in somatic cells. Experimental data do demonstrate such genomic variations to exist and to be involved in human development and interindividual genetic variability in health and disease. However, since current genomic technologies are mainly based on methods, which analyze genomes from a large pool of cells, intercellular or somatic genome variations are significantly less appreciated in modern bioscience. Here, a review of somatic genome variations occurring at all levels of genome organization (i.e. DNA sequence, subchromosomal and chromosomal) in health and disease is presented. Looking through the available literature, it was possible to show that the somatic cell genome is extremely variable. Additionally, being mainly associated with chromosome or genome instability (most commonly manifesting as aneuploidy), somatic genome variations are involved in pathogenesis of numerous human diseases. The latter mainly concerns diseases of the brain (i.e. autism, schizophrenia, Alzheimer's disease) and immune system (autoimmune diseases), chromosomal and some monogenic syndromes, cancers, infertility and prenatal mortality. Taking into account data on somatic genome variations and chromosome instability, it becomes possible to show that related processes can underlie non-malignant pathology such as (neuro)degeneration or other local tissue dysfunctions. Together, we suggest that detection and characterization of somatic genome behavior and variations can provide new opportunities for human genome research and genetics.

Confined placental mosaicism and pregnancy outcome: a distinction needs to be made between types 2 and 3

OBJECTIVE

To study the influence of types 2 and 3 confined placental mosaicism (CPM) on pregnancy outcome.

METHOD

From 13 809 chorionic villus samplings (CVSs), karyotype after long-term cultured villi (LTC-villi) was systematically performed. Next, in case of suspicion of CPM, karyotype after short-term cultured villi (STC-villi) was established to define type 2 CPM (chromosomal abnormality limited to the mesenchymal core) or type 3 CPM (chromosomal abnormality found both in the cytotrophoblast and the mesenchymal core). Confirmatory amniocentesis was performed to exclude fetal mosaicism. Uniparental disomy (UPD) testing was carried out when the abnormal cell line involved chromosomes 5, 6, 7, 15 or 16.

RESULTS

Fifty-seven CPM cases were observed (57/13 809 = 0.41%) and of these, 37 were type 2 and 20 were type 3 CPM. Incidence of preterm infants, neonatal hypotrophy and adverse pregnancy outcome were comparable between patients in whom type 2 CPM was demonstrated and the control population. In contrast, for the type 3 CPM the incidence of these factors was higher than for the control population.

CONCLUSION

When a CPM is suspected, it appears essential to determine type, since type 2 has no effect on fetal development and type 3 is associated with preterm infants, low birth weight and adverse pregnancy outcome.

Cytogenetic analysis of 355 cases of fetal loss in different trimesters

OBJECTIVE

We estimated the success rates of cytogenetic analyses in different tissue samples after intrauterine fetal deaths and analyzed the value of cytogenetic testing for determining the causes.

METHODS

Women with intrauterine fetal deaths (occurring at > 10 weeks of gestation) were offered either invasive testing before medical induction of labor, or solid tissue biopsy diagnosis after delivery.

RESULTS

A total cohort of 355 intrauterine fetal deaths was studied. During antepartum examinations, invasive procedures included amniocentesis (AMC), chorionic villus sampling (CVS) and umbilical cord (UBC) sampling. During postpartum examinations, samples were taken from unfixed specimens of fetal skin, placenta and other tissues. Chromosomal abnormalities were observed in 22 fetal deaths for which cytogenetic analyses were successful. Logistic regression analysis identified antepartum invasive sampling [P = 0.000, odds ratio (OR) 31.125, 95% confidence interval (CI) 14.265-67.908] to be associated with a high cytogenetic success rate and older age with fetal deaths (P = 0.104, OR 0.487, 95% CI 0.204-1.160) not to be associated with a high chromosomal abnormality. In the patients with recurrent pregnancy loss, the chromosomal abnormality rate of 18.6% of spontaneous abortions has not been significantly more than that of fetal deaths 11.5% (P = 0.437).

CONCLUSION

Parents should be counseled on all aspects of cytogenetic analysis after fetal death. Antepartum testing after pregnancy loss is recommended.

SNP microarray-based 24 chromosome aneuploidy screening demonstrates that cleavage-stage FISH poorly predicts aneuploidy in embryos that develop to morphologically normal blastocysts

Although selection of chromosomally normal embryos has the potential to improve outcomes for patients undergoing IVF, the clinical impact of aneuploidy screening by fluorescence in situ hybridization (FISH) has been controversial. There are many putative explanations including sampling error due to mosaicism, negative impact of biopsy, a lack of comprehensive chromosome screening, the possibility of embryo self-correction and poor predictive value of the technology itself. Direct analysis of the negative predictive value of FISH-based aneuploidy screening for an embryo's reproductive potential has not been performed. Although previous studies have found that cleavage-stage FISH is poorly predictive of aneuploidy in morphologically normal blastocysts, putative explanations have not been investigated. The present study used a single nucleotide polymorphism (SNP) microarray-based 24 chromosome aneuploidy screening technology to re-evaluate morphologically normal blastocysts that were diagnosed as aneuploid by FISH at the cleavage stage. Mosaicism and preferential segregation of aneuploidy to the trophectoderm (TE) were evaluated by characterization of multiple sections of the blastocyst. SNP microarray technology also provided the first opportunity to evaluate self-correction mechanisms involving extrusion or duplication of aneuploid chromosomes resulting in uniparental disomy (UPD). Of all blastocysts evaluated (n = 50), 58% were euploid in all sections despite an aneuploid FISH result. Aneuploid blastocysts displayed no evidence of preferential segregation of abnormalities to the TE. In addition, extrusion or duplication of aneuploid chromosomes resulting in UPD did not occur. These findings support the conclusion that cleavage-stage FISH technology is poorly predictive of aneuploidy in morphologically normal blastocysts.

Detection of chromosome aneuploidies in chorionic villus samples by multiplex ligation-dependent probe amplification

The objective of this study was to examine the suitability of multiplex ligation-dependent probe amplification (MLPA) in chorionic villus samples as a replacement for traditional karyotyping for the detection of (an)euploidies of chromosomes 21, 18, 13, X, and Y. Chorionic villus samples were diagnosed by traditional karyotyping using short-term cultures (STC) and long-term cultures (LTC), and by MLPA using kit P095. DNA was extracted after digestion of whole villi with proteinase K and/or trypsin and collagenase. Different cell-dissociation procedures were tested to obtain MLPA results representative of the cytotrophoblast layer and the mesenchymal core. Over 95% of the MLPA results were in concordance with the traditional karyotyping of STC and LTC. Traditional karyotyping revealed seven mosaics. After digestion of whole villi with proteinase K, only abnormal cell lines confined to the STC gave rise to abnormal MLPA results. In one sample, the complete discrepancy between STC and LTC was resolved after enzymatic dissociation of cells from the cytotrophoblast layer and the mesenchymal core. MLPA in chorionic villus samples was found to be a reliable test for the detection of (an)euploidies of chromosomes 21, 18, 13, X, and Y. Whole villi digestion with proteinase K resulted in the over-representation of cytotrophoblasts in the DNA pool. To obtain MLPA results representative for STC and LTC, enzymatic dissociation of cells from the cytotrophoblast layer and mesenchymal core is required.

Chromosomal mosaicism goes global

Intercellular differences of chromosomal content in the same individual are defined as chromosomal mosaicism (alias intercellular or somatic genomic variations or, in a number of publications, mosaic aneuploidy). It has long been suggested that this phenomenon poorly contributes both to intercellular (interindividual) diversity and to human disease. However, our views have recently become to change due to a series of communications demonstrated a higher incidence of chromosomal mosaicism in diseased individuals (major psychiatric disorders and autoimmune diseases) as well as depicted chromosomal mosaicism contribution to genetic diversity, the central nervous system development, and aging. The later has been produced by significant achievements in the field of molecular cytogenetics. Recently, Molecular Cytogenetics has published an article by Maj Hulten and colleagues that has provided evidences for chromosomal mosaicism to underlie formation of germline aneuploidy in human female gametes using trisomy 21 (Down syndrome) as a model. Since meiotic aneuploidy is suggested to be the leading genetic cause of human prenatal mortality and postnatal morbidity, these data together with previous findings define chromosomal mosaicism not as a casual finding during cytogenetic analyses but as a more significant biological phenomenon than previously recognized. Finally, the significance of chromosomal mosaicism can be drawn from the fact, that this phenomenon is involved in genetic diversity, normal and abnormal prenatal development, human diseases, aging, and meiotic aneuploidy, the intrinsic cause of which remains, as yet, unknown.

Lack of aneuploidy for chromosomes 15, 16, and 18 in placentas from small-for-gestational-age liveborn infants

OBJECTIVE

The purpose of this study was to investigate the frequency of confined placental mosaicism (CPM) in placentas from liveborn infants.

STUDY DESIGN

A retrospective analysis of 51 placentas from small-for-gestational-age (SGA), live born infants (birthweight below 5th centile), and 45 placentas from normally grown infants at term was performed. Aneuploidy for chromosomes 15, 16, and 18 was analyzed with QF-PCR (polymorphic markers) and FISH (centromeric probes).

RESULTS

No trisomic sample was detected with either method. FISH revealed 1 case of monosomy 16 in the SGA group, which was not confirmed by PCR. On the other hand, PCR analysis showed allelic imbalances, ie, deviation of the 1:1 peak ratio > 20%, in 5 cases (4 in the SGA and 1 in the control group; P = .157).

CONCLUSION

Trisomic CPM in liveborn SGA infants is much less frequent than previously appreciated. The occurrence and eventual biologic significance of the observed allelic imbalances needs to be further investigated.

Clinical outcome of infants with confined placental mosaicism and intrauterine growth restriction of unknown cause

The purpose of this study was to know a role of confined placental mosaicism (CPM) in perinatal outcome and postnatal growth and development of infants with intrauterine growth restriction (IUGR). We selected 50 infants with IUGR (<-2.0 SD) from 3,257 deliveries in a regional medical center during the past 10-year period, and carried out cytogenetic and molecular analyses in their placenta and cord blood. Of the 50 infants, 8 had CPM (CPM group) and were composed of five single (CPM2, 7, 13, 22, and 22), one double (CPM7/13), and one quadruple trisomy (CPM2/7/15/20), and one partial monosomy [del(2)(p16)]. The origin of an extra chromosome of trisomy was maternal in six cases of CPM, paternal in one, and undetermined in one. Uniparental disomy in disomic cell lines was ruled out in all these mosaics. We also compared clinical parameters for perinatal outcome between CPM group and infants without evidence of CPM (non-CPM group), such as maternal and gestational age, birth weight, Apgar score, cord blood pH, gender, and uterine artery patterns by Doppler ultrasonography, as well as weight, height, and developmental quotient (DQ) by Denver Developmental Screening Test at age 12 months. Phenotypic abnormalities were noted in two infants with CPM and three infants of non-CPM group: One with CPM22 had ASD and hypospadias, one with CPM7/13 had Russell-Silver syndrome (RSS), and one without CPM had polydactyly, and two without CPM had RSS. All but one infant with CPM are alive at age 12 months. Among the clinical parameters, the detection rate of a notch waveform pattern of the uterine artery was significantly higher in the CPM group (P < 0.05). However, no significant difference was noted in perinatal outcome of pregnancy and in DQ at age 12 months between the two groups. Interestingly, short stature (<-2 SD) at age 12 months was more frequently seen in CPM group (7/8 infants with CPM vs. 8/15 infants without CPM), although no statistically significant difference was obtained. The information obtained will be useful for perinatal care and genetic counseling for infants with IUGR and CPM.

Confirmation of mosaicism and uniparental disomy in amniocytes, after detection of mosaic chromosome abnormalities in chorionic villi

Chromosome mosaicism is detected in about 1-2% of chorionic villi samples (CVS), and may be due to a postzygotic nondisjunction event generating a trisomic cell line in an initially normal conceptus (mitotic origin) or the postzygotic loss of one chromosome in an initially trisomic conceptus (meiotic origin and trisomy rescue). Depending on the distribution of the abnormal cell line, the mosaic can be confined to the placenta (CPM) or generalised to the fetus (TFM, true fetal mosaicism). Trisomy rescue could theoretically be associated with a 33.3% probability of uniparental disomy (UPD) in the fetus. The aim of this study was to determine the risk of fetal involvement in a cohort of numerical and structural chromosome mosaics revealed in chorionic villi by means of combined direct and long-term culture analyses; we also determined the incidence of UPD associated with mosaic aneuploidies and supernumerary markers involving imprinted chromosomes. A total of 273 of a consecutive series of 15,109 CVS evaluated during a period of 5 years showed a mosaic condition in direct preparations and/or long-term cultures; confirmatory amniocentesis was performed in 203 cases. The abnormal cell line was extended to the fetus in 12.8% cases in terms of structural and numerical abnormalities involving autosomes and sex chromosomes; the risk of TFM varied and depended on the placental tissue distribution of the abnormal cell line. One of the 51 cases in which the mosaic involved an imprinted chromosome showed UPD, thus indicating a risk of 1.96%.

Chromosomal variation in mammalian neuronal cells: known facts and attractive hypotheses

Chromosomal mosaicism is still a genetic enigma. Although the mechanisms and consequences of this phenomenon have been studied for over 50 years, there are a number of gaps in our knowledge concerning causes, genetic mechanisms, and phenotypic manifestations of chromosomal mosaicism. Neuronal cell-specific chromosomal mosaicism is not an exception. Originally, neuronal cells of the mammalian brain were assumed to possess identical genomes. However, recent studies have shown chromosomal variations, manifested as chromosome abnormalities in cells of the developing and adult mammalian nervous system. Here, we review data obtained on the variation in chromosome complement in mammalian neuronal cells and hypothesize about the possible relevance of large-scale genomic (i.e., chromosomal) variations to brain development and functions as well as neurodevelopmental and neurodegenerative disorders. We propose to cover the term "molecular neurocytogenetics to cover all studies the aim of which is to reveal chromosome variations and organization in the mammalian brain.

Rapid prenatal diagnosis of common trisomies: discordant results between QF-PCR analysis and karyotype analysis on long-term culture for a case of trisomy 18 detected in CVS

OBJECTIVES

QF-PCR analysis can be used as a rapid test to diagnose primary trisomy in prenatal samples. Mosaicism in CVS detected by QF-PCR has previously been reported; however, no case has so far been reported in which the QF-PCR result was completely discrepant to that of the karyotype analysis from a long-term culture.

METHODS

A CVS, referred because of a high serum screening risk of 1:10 for Down Syndrome and 1:110 for Edwards Syndrome, was tested by QF-PCR analysis and chromosome analysis of cultured cells. Subsequent analyses were carried out on a follow-up amniotic fluid sample and foetal tissue samples.

RESULTS

Conflicting results were obtained between QF-PCR analysis on two independent fronds from the chorionic villi and chromosome analysis on cultured CVS. Cytogenetic and molecular analysis on a subsequent amniotic fluid sample indicated trisomy 18 with no evidence of mosaicism. Analysis of follow-up tissue confirmed trisomy in a foetal skin sample and mosaicism for trisomy 18 in four placental sites tested.

CONCLUSION

We report here an apparently normal CVS QF-PCR result that was completely discrepant with the trisomy 18 positive karyotype result on long-term culture. This has important implications regarding our current testing protocol.

Health and developmental outcome of children following prenatal diagnosis of confined placental mosaicism

OBJECTIVE

To determine the long-term health and development of a cohort of children in whom confined placental mosaicism (CPM) was diagnosed at prenatal diagnosis.

METHODS

A retrospective cohort study was performed comparing 36 children in whom CPM had been diagnosed prenatally with 195 controls subjects in whom a normal karyotype had been detected prenatally. Data comprising birth information, health, health service utilisation, growth, development, behaviour, and the family were collected by a maternal questionnaire administered when the subjects were aged between 4 and 11 years.

RESULTS

CPM cases did not differ from controls across a broad range of health measures and there were no major health problems or birth defects among the CPM group. No increase was detected in the incidence of intrauterine growth retardation (IUGR) among CPM cases; however, postnatal growth was reduced compared with controls (p = 0.047). Development and behaviour in CPM cases was similar to that of controls.

CONCLUSIONS

The prenatal diagnosis of CPM is not associated with an increased risk of birth defects or developmental problems, but may be associated with decreased growth.