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Fertility and Sterility Nov 2021Preimplantation genetic testing for aneuploidy (PGT-A) remains one of the most controversial topics in reproductive medicine. With more than 40% of in vitro... (Review)
Review
Preimplantation genetic testing for aneuploidy (PGT-A) remains one of the most controversial topics in reproductive medicine. With more than 40% of in vitro fertilization cycles in the United States reportedly involving PGT, both those in favor of and those opposed to PGT-A have significant interest in the efficacy of PGT-A. Ongoing issues include what patient population, if any, benefits from PGT-A, the true frequency of chromosomal mosaicism, whether embryonic aneuploidies self-correct, and how practitioners manage embryos designated as "mosaic." This review addresses several misconceptions and misinterpretations of data surrounding the genetic analysis and prediction of mosaicism in the preimplantation embryo.
Topics: Aneuploidy; Blastocyst; Embryo Transfer; Female; Genetic Counseling; Genetic Testing; Humans; Infertility; Male; Mosaicism; Predictive Value of Tests; Pregnancy; Prenatal Diagnosis; Reproducibility of Results; Reproductive Techniques, Assisted; Risk Assessment; Risk Factors; Treatment Outcome
PubMed: 34304887
DOI: 10.1016/j.fertnstert.2021.06.027 -
American Journal of Human Genetics Dec 2021Chromosome imbalance (aneuploidy) is the major cause of pregnancy loss and congenital disorders in humans. Analyses of small biopsies from human embryos suggest that...
Chromosome imbalance (aneuploidy) is the major cause of pregnancy loss and congenital disorders in humans. Analyses of small biopsies from human embryos suggest that aneuploidy commonly originates during early divisions, resulting in mosaicism. However, the developmental potential of mosaic embryos remains unclear. We followed the distribution of aneuploid chromosomes across 73 unselected preimplantation embryos and 365 biopsies, sampled from four multifocal trophectoderm (TE) samples and the inner cell mass (ICM). When mosaicism impacted fewer than 50% of cells in one TE biopsy (low-medium mosaicism), only 1% of aneuploidies affected other portions of the embryo. A double-blinded prospective non-selection trial (NCT03673592) showed equivalent live-birth rates and miscarriage rates across 484 euploid, 282 low-grade mosaic, and 131 medium-grade mosaic embryos. No instances of mosaicism or uniparental disomy were detected in the ensuing pregnancies or newborns, and obstetrical and neonatal outcomes were similar between the study groups. Thus, low-medium mosaicism in the trophectoderm mostly arises after TE and ICM differentiation, and such embryos have equivalent developmental potential as fully euploid ones.
Topics: Aneuploidy; Blastocyst; Double-Blind Method; Embryo Transfer; Embryonic Development; Female; Fertilization in Vitro; Genetic Testing; Humans; Incidence; Infant, Newborn; Male; Mosaicism; Pregnancy; Pregnancy Outcome; Prospective Studies
PubMed: 34798051
DOI: 10.1016/j.ajhg.2021.11.002 -
Fertility and Sterility May 2021To study how the attributes of mosaicism identified during preimplantation genetic testing for aneuploidy relate to clinical outcomes, in order to formulate a ranking...
OBJECTIVE
To study how the attributes of mosaicism identified during preimplantation genetic testing for aneuploidy relate to clinical outcomes, in order to formulate a ranking system of mosaic embryos for intrauterine transfer.
DESIGN
Compiled analysis.
SETTING
Multi-center.
PATIENT(S)
A total of 5,561 euploid blastocysts and 1,000 mosaic blastocysts used in clinical transfers in patients undergoing fertility treatment.
INTERVENTION(S)
None.
MAIN OUTCOME MEASURE(S)
Implantation (gestational sac), ongoing pregnancy, birth, and spontaneous abortion (miscarriage before 20 weeks of gestation).
RESULT(S)
The euploid group had significantly more favorable rates of implantation and ongoing pregnancy/birth (OP/B) compared with the combined mosaic group or the mosaic group affecting only whole chromosomes (implantation: 57.2% vs. 46.5% vs. 41.8%; OP/B: 52.3% vs. 37.0% vs. 31.3%), as well as lower likelihood of spontaneous abortion (8.6% vs. 20.4% vs. 25%). Whole-chromosome mosaic embryos with level (percent aneuploid cells) <50% had significantly more favorable outcomes than the ≥50% group (implantation: 44.5% vs. 30.4%; OP/B: 36.1% vs. 19.3%). Mosaic type (nature of the aneuploidy implicated in mosaicism) affected outcomes, with a significant correlation between number of affected chromosomes and unfavorable outcomes. This ranged from mosaicism involving segmental abnormalities to complex aneuploidies affecting three or more chromosomes (implantation: 51.6% vs. 30.4%; OP/B: 43.1% vs. 20.8%). Combining mosaic level, type, and embryo morphology revealed the order of subcategories regarding likelihood of positive outcome.
CONCLUSION(S)
This compiled analysis revealed traits of mosaicism identified with preimplantation genetic testing for aneuploidy that affected outcomes in a statistically significant manner, enabling the formulation of an evidence-based prioritization scheme for mosaic embryos in the clinic.
Topics: Adult; Aneuploidy; Blastocyst; Data Interpretation, Statistical; Embryo Implantation; Embryo Transfer; Embryonic Development; Female; Fertilization in Vitro; Genetic Testing; Humans; Infant, Newborn; Infertility; Karyotyping; Male; Mosaicism; Pregnancy; Pregnancy Outcome; Pregnancy Rate; Preimplantation Diagnosis; Prognosis; Treatment Outcome
PubMed: 33685629
DOI: 10.1016/j.fertnstert.2020.11.041 -
Genes May 2020There is a high incidence of chromosomal abnormalities in early human embryos, whether they are generated by natural conception or by assisted reproductive technologies... (Review)
Review
There is a high incidence of chromosomal abnormalities in early human embryos, whether they are generated by natural conception or by assisted reproductive technologies (ART). Cells with chromosomal copy number deviations or chromosome structural rearrangements can compromise the viability of embryos; much of the naturally low human fecundity as well as low success rates of ART can be ascribed to these cytogenetic defects. Chromosomal anomalies are also responsible for a large proportion of miscarriages and congenital disorders. There is therefore tremendous value in methods that identify embryos containing chromosomal abnormalities before intrauterine transfer to a patient being treated for infertility-the goal being the exclusion of affected embryos in order to improve clinical outcomes. This is the rationale behind preimplantation genetic testing for aneuploidy (PGT-A) and structural rearrangements (-SR). Contemporary methods are capable of much more than detecting whole chromosome abnormalities (e.g., monosomy/trisomy). Technical enhancements and increased resolution and sensitivity permit the identification of chromosomal mosaicism (embryos containing a mix of normal and abnormal cells), as well as the detection of sub-chromosomal abnormalities such as segmental deletions and duplications. Earlier approaches to screening for chromosomal abnormalities yielded a binary result of normal versus abnormal, but the new refinements in the system call for new categories, each with specific clinical outcomes and nuances for clinical management. This review intends to give an overview of PGT-A and -SR, emphasizing recent advances and areas of active development.
Topics: Abortion, Spontaneous; Aneuploidy; Blastocyst; Chromosome Aberrations; Chromosome Disorders; Chromosomes; Humans; Mosaicism; Preimplantation Diagnosis
PubMed: 32485954
DOI: 10.3390/genes11060602 -
Nature Neuroscience Sep 2017We systematically analyzed postzygotic mutations (PZMs) in whole-exome sequences from the largest collection of trios (5,947) with autism spectrum disorder (ASD)...
We systematically analyzed postzygotic mutations (PZMs) in whole-exome sequences from the largest collection of trios (5,947) with autism spectrum disorder (ASD) available, including 282 unpublished trios, and performed resequencing using multiple independent technologies. We identified 7.5% of de novo mutations as PZMs, 83.3% of which were not described in previous studies. Damaging, nonsynonymous PZMs within critical exons of prenatally expressed genes were more common in ASD probands than controls (P < 1 × 10), and genes carrying these PZMs were enriched for expression in the amygdala (P = 5.4 × 10). Two genes (KLF16 and MSANTD2) were significantly enriched for PZMs genome-wide, and other PZMs involved genes (SCN2A, HNRNPU and SMARCA4) whose mutation is known to cause ASD or other neurodevelopmental disorders. PZMs constitute a significant proportion of de novo mutations and contribute importantly to ASD risk.
Topics: Autism Spectrum Disorder; Databases, Genetic; Genetic Predisposition to Disease; Genetic Variation; Humans; Mosaicism; Mutation, Missense; Zygote
PubMed: 28714951
DOI: 10.1038/nn.4598 -
International Journal of Molecular... Mar 2022This review focuses on recent findings in the preimplantation genetic testing (PGT) of embryos. Different preimplantation genetic tests are presented along with... (Review)
Review
This review focuses on recent findings in the preimplantation genetic testing (PGT) of embryos. Different preimplantation genetic tests are presented along with different genetic materials and their analysis. Original material concerning preimplantation genetic testing for aneuploidy (PGT-A) was sourced by searching the PubMed and ScienceDirect databases in October and November 2021. The searches comprised keywords such as 'preimplantation', 'cfDNA'; 'miRNA', 'PGT-A', 'niPGT-A', 'aneuploidy', 'mosaicism', 'blastocyst biopsy', 'blastocentesis', 'blastocoel fluid', 'NGS', 'FISH', and 'aCGH'. Non-invasive PGT-A (niPGT-A) is a novel approach to the genetic analysis of embryos. The premise is that the genetic material in the spent embryo culture media (SECM) corresponds to the genetic material in the embryo cells. The limitations of niPGT-A are a lower quantity and lesser quality of the cell-free genetic material, and its unknown origin. The concordance rate varies when compared to invasive PGT-A. Some authors have also hypothesized that mosaicism and aneuploid cells are preferentially excluded from the embryo during early development. Cell-free genetic material is readily available in the spent embryo culture media, which provides an easier, more economic, and safer extraction of genetic material for analysis. The sampling of the SECM and DNA extraction and amplification must be optimized. The origin of the cell-free media, the percentage of apoptotic events, and the levels of DNA contamination are currently unknown; these topics need to be further investigated.
Topics: Aneuploidy; Blastocyst; Culture Media; Female; Genetic Testing; Humans; Mosaicism; Pregnancy; Preimplantation Diagnosis
PubMed: 35408927
DOI: 10.3390/ijms23073568 -
Human Reproduction Update Aug 2021Chromosomal mosaicism can be detected in different stages of early life: in cleavage stage embryos, in blastocysts and biopsied cells from blastocysts during... (Review)
Review
BACKGROUND
Chromosomal mosaicism can be detected in different stages of early life: in cleavage stage embryos, in blastocysts and biopsied cells from blastocysts during preimplantation genetic testing for aneuploidies (PGT-A) and later during prenatal testing, as well as after birth in cord blood. Mosaicism at all different stages can be associated with adverse pregnancy outcomes. There is an onward discussion about whether blastocysts diagnosed as chromosomally mosaic by PGT-A should be considered safe for transfer. An accurate diagnosis of mosaicism remains technically challenging and the fate of abnormal cells within an embryo remains largely unknown. However, if aneuploid cells persist in the extraembryonic tissues, they can give rise to confined placental mosaicism (CPM). Non-invasive prenatal testing (NIPT) uses cell-free (cf) DNA released from the placenta in maternal blood, facilitating the detection of CPM. In literature, conflicting evidence is found about whether CPM is associated with fetal growth restriction (FGR) and/or other pregnancy outcomes. This makes counselling for patients by clinicians challenging and more knowledge is needed for clinical decision and policy making.
OBJECTIVE AND RATIONALE
The objective of this review is to evaluate the association between CPM and prenatal growth and adverse pregnancy outcomes. All relevant literature has been reviewed in order to achieve an overview on merged results exploring the relation between CPM and FGR and other adverse pregnancy outcomes.
SEARCH METHODS
The following Medical Subject Headings (MESH) terms and all their synonyms were used: placental, trophoblast, cytotrophoblast, mosaicism, trisomy, fetal growth, birth weight, small for gestational age and fetal development. A search in Embase, PubMed, Medline Ovid, Web of Science, Cochrane Central Register of Controlled Trials (CENTRAL) and Google Scholar databases was conducted. Relevant articles published until 16 July 2020 were critically analyzed and discussed.
OUTCOMES
There were 823 articles found and screened based on their title/abstract. From these, 213 articles were selected and full text versions were obtained for a second selection, after which 70 publications were included and 328 cases (fetuses) were analyzed. For CPM in eight different chromosomes (of the total 14 analyzed), there was sufficient evidence that birth weight was often below the 5th percentile of fetal growth standards. FGR was reported in 71.7% of CPM cases and preterm birth (<37 weeks of delivery) was reported in 31.0% of cases. A high rate of structural fetal anomalies, 24.2%, in cases with CPM was also identified. High levels of mosaicism in CVS and presence of uniparental disomy (UPD) were significantly associated with adverse pregnancy outcomes.
WIDER IMPLICATIONS
Based on the literature, the advice to clinicians is to monitor fetal growth intensively from first trimester onwards in case of CPM, especially when chromosome 2, 3, 7, 13, 15, 16 and 22 are involved. In addition to this, it is advised to examine the fetuses thoroughly for structural fetal anomalies and raise awareness of a higher chance of (possibly extreme) premature birth. Despite prematurity in nearly a fifth of cases, the long-term follow-up of CPM life borns seems to be positive. More understanding of the biological mechanisms behind CPM will help in prioritizing embryos for transfer after the detection of mosaicism in embryos through PGT-A.
Topics: Female; Fetal Development; Humans; Infant, Newborn; Mosaicism; Placenta; Pregnancy; Pregnancy Outcome; Premature Birth
PubMed: 33984128
DOI: 10.1093/humupd/dmab009 -
Fertility and Sterility Aug 2020Since the advent of preimplantation genetic testing for aneuploidy (PGT-A) in the 1990s, substantial changes in test methodology and technology now allow the detection... (Review)
Review
Since the advent of preimplantation genetic testing for aneuploidy (PGT-A) in the 1990s, substantial changes in test methodology and technology now allow the detection and reporting of intermediate chromosome copy number (commonly referred to as mosaicism) for aneuploidy in a trophectoderm biopsy sample. Clinicians are grappling with how to interpret such findings and how to counsel patients about embryo transfer decision-making. This document reviews the available literature and outlines the various issues surrounding the reporting of intermediate copy number and consideration of storage or transfer of blastocysts with intermediate copy number results. This document does not endorse, nor does it suggest that PGT-A is appropriate for all cases of in vitro fertilization.
Topics: Aneuploidy; Biopsy; Blastocyst; Clinical Decision-Making; Consensus; Embryo Transfer; Female; Fertilization in Vitro; Genetic Counseling; Genetic Testing; Humans; Male; Mosaicism; Predictive Value of Tests; Pregnancy; Pregnancy Outcome; Preimplantation Diagnosis; Reproductive Medicine; Risk Assessment; Risk Factors; Treatment Outcome
PubMed: 32741460
DOI: 10.1016/j.fertnstert.2020.05.014 -
Human Molecular Genetics Apr 2010Mosaic aneuploidy and uniparental disomy (UPD) arise from mitotic or meiotic events. There are differences between these mechanisms in terms of (i) impact on embryonic...
Mosaic aneuploidy and uniparental disomy (UPD) arise from mitotic or meiotic events. There are differences between these mechanisms in terms of (i) impact on embryonic development; (ii) co-occurrence of mosaic trisomy and UPD and (iii) potential recurrence risks. We used a genome-wide single nucleotide polymorphism (SNP) array to study patients with chromosome aneuploidy mosaicism, UPD and one individual with XX/XY chimerism to gain insight into the developmental mechanism and timing of these events. Sixteen cases of mosaic aneuploidy originated mitotically, and these included four rare trisomies and all of the monosomies, consistent with the influence of selective factors. Five trisomies arose meiotically, and three of the five had UPD in the disomic cells, confirming increased risk for UPD in the case of meiotic non-disjunction. Evidence for the meiotic origin of aneuploidy and UPD was seen in the patterns of recombination visible during analysis with 1-3 crossovers per chromosome. The mechanisms of formation of the UPD included trisomy rescue, with and without concomitant trisomy, monosomy rescue, and mitotic formation of a mosaic segmental UPD. UPD was also identified in an XX/XY chimeric individual, with one cell line having complete maternal UPD consistent with a parthenogenetic origin. Utilization of SNP arrays allows simultaneous evaluation of genomic alterations and insights into aneuploidy and UPD mechanisms. Differentiation of mitotic and meiotic origins for aneuploidy and UPD supports existence of selective factors against full trisomy of some chromosomes in the early embryo and provides data for estimation of recurrence and disease mechanisms.
Topics: Aneuploidy; Chimerism; Humans; Meiosis; Monosomy; Mosaicism; Polymorphism, Single Nucleotide; Sex Chromosomes; Trisomy; Uniparental Disomy
PubMed: 20053666
DOI: 10.1093/hmg/ddq003 -
Nature Aug 2017Developmental deconvolution of complex organs and tissues at the level of individual cells remains challenging. Non-invasive genetic fate mapping has been widely used,...
Developmental deconvolution of complex organs and tissues at the level of individual cells remains challenging. Non-invasive genetic fate mapping has been widely used, but the low number of distinct fluorescent marker proteins limits its resolution. Much higher numbers of cell markers have been generated using viral integration sites, viral barcodes, and strategies based on transposons and CRISPR-Cas9 genome editing; however, temporal and tissue-specific induction of barcodes in situ has not been achieved. Here we report the development of an artificial DNA recombination locus (termed Polylox) that enables broadly applicable endogenous barcoding based on the Cre-loxP recombination system. Polylox recombination in situ reaches a practical diversity of several hundred thousand barcodes, allowing tagging of single cells. We have used this experimental system, combined with fate mapping, to assess haematopoietic stem cell (HSC) fates in vivo. Classical models of haematopoietic lineage specification assume a tree with few major branches. More recently, driven in part by the development of more efficient single-cell assays and improved transplantation efficiencies, different models have been proposed, in which unilineage priming may occur in mice and humans at the level of HSCs. We have introduced barcodes into HSC progenitors in embryonic mice, and found that the adult HSC compartment is a mosaic of embryo-derived HSC clones, some of which are unexpectedly large. Most HSC clones gave rise to multilineage or oligolineage fates, arguing against unilineage priming, and suggesting coherent usage of the potential of cells in a clone. The spreading of barcodes, both after induction in embryos and in adult mice, revealed a basic split between common myeloid-erythroid development and common lymphocyte development, supporting the long-held but contested view of a tree-like haematopoietic structure.
Topics: Animals; Attachment Sites, Microbiological; Cell Lineage; Cell Tracking; Clone Cells; DNA Barcoding, Taxonomic; Embryo, Mammalian; Erythroid Cells; Female; Hematopoietic Stem Cells; Integrases; Lymphocytes; Male; Mice; Mosaicism; Myeloid Cells; Recombination, Genetic; Single-Cell Analysis
PubMed: 28813413
DOI: 10.1038/nature23653