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Gographie - Socit. Naruto 10 ans Shinobis. Rouen, Sabina, Tome 1 :. Houses : L'architecture d'aujourd'hui! Maisons [pdf] de Philip Jodidio. Chromosome 2 is the second largest human chromosome, containing — genes Genetics Home Reference. Partial deletions of this chromosome have been linked to a variety of syndromes causing intellectual disability, skeletal or craniofacial abnormalities and developmental delays Falk and Casas, ; Leroy et al.
A wide spectrum of limb, genitourinary, craniofacial, cardiac and spinal abnormalities, hydronephrosis and fetal growth restriction have been reported in the ultrasonographic follow-up of cases of prenatally detected mosaic aneuploidies of chromosome 2 Sifakis et al. The follow-up through gestation went uneventfully with no signs of morphological abnormalities.
The amniotic fluid volume and intrauterine growth was around the 50th percentile with no signs of oligohydramnios or fetal growth restriction. There was also no sign of morphological abnormalities in the newborn.
Grati et al. Accordingly, they devised a risk scoring system for prioritizing mosaic embryos by comparing the results of CVS with further amniocentesis to assess the incidence of true fetal mosaicism. They also conducted a uniparental disomy investigation reviewing mosaic aneuploidies likely to be associated with miscarriage. It was concluded that mosaicism involving chromosomes 13, 14, 15, 16, 18 and 21 and monosomy X were all high risk.
Eight trisomy 2 abnormal cell lines and eight confined placental mosaicisms with no true fetal mosaicism or fetal involvement were identified. Furthermore, an evidence-based scoring system for prioritizing mosaic embryos for transfer following PGT noted two cases of miscarriage Grati et al. Three main mechanisms are proposed in mosaicism of the human embryos: anaphase lagging, mitotic non-disjunction and endoreplication.
However, the effect of each on the chromosomal constitution of the cells is different, thus leading to a distinct aneuploidy in the blastocyst. The blastocyst derived from this embryo will therefore be mosaic, with two distinct cell lines, one disomic and one monosomic.
In the mitotic non-disjunction event, the sister chromatids fail to separate during mitosis, creating two distinct cell lines, one with a monosomy and another with a trisomy of the chromosome which has failed to split. The incidence of this type of mitotic error in embryos is not known but is believed to be dependent on the embryo developmental stage Taylor et al. Finally, endoreplication occurs when a chromosome replicates itself, but this replication is not followed by a cell division.
As a result, this cell gains one extra chromosome, thus becoming trisomic, whereas the adjacent cells remain disomic. Endoreplication is thought to be mainly due to cell cycle checkpoint failures Taylor et al.
The only mechanism out of these three main causes of mosaicism that can lead to the occurrence of both monosomic and trisomic cell lines for a specific chromosome is the non-disjunction error. A mitotic non-disjunction error taking place during the cleavage stage and before the differentiation of the inner cell mass and the trophoblast could explain the mirroring mosaicisms observed in our patient for chromosome 2. The trophectoderm biopsy was mosaic for the monosomy of chromosome 2, whereas the amniocentesis revealed a mosaic trisomy 2.
Finally, the peripheral blood chromosome analysis was mosaic for monosomy 2 postnatally, and the epithelial cells in a buccal smear were diploid. The lower ratio of mosaicism observed in amniocentesis and the peripheral blood chromosome analysis when compared to the trophectoderm biopsy may be the result of one of the two following proposed mechanisms: the preferential localization of abnormal cells in trophectoderm or the preferential growth of euploid cells Harton et al. The placenta was not available for testing.
The prioritization of mosaic embryos is not very straightforward. The embryonic mortality model indicates that embryos with high mosaicism or full aneuploidy do not survive to implant; however, fully euploid and low-level mosaic embryos have a chance to implant.
In other words, the embryonic mortality models invoke selection against embryos based on the proportion of aneuploid cells. This is the most commonly accepted model for implantation of mosaic embryos, and it is based on the fact that the aneuploid cell lines produced after a mitotic error during cleavage do not survive and are lost during implantation, so the fetus is fully composed of euploid cells.
The clonal depletion model describes apoptosis or reduced propagation of aneuploid cells within a mosaic embryo Bolton et al. In other words, this shows the self-correction of cell lines that are initially aneuploid but which, through rescue mechanisms, evolve into euploid cells McCoy , Patient counseling regarding mosaic embryo transfer is extremely important. Considering the mechanisms of mosaicism, it must be remembered that discrepancies between embryo chromosomal status and prenatal or postnatal chromosomal evaluations, such as between monosomy and trisomy, can also occur.
Our case report illustrates that mosaicism in human embryos arising from a mitotic non-disjunction error leads to both monosomic and trisomic cell lines.
However, because of the nature of the trophectoderm biopsy itself, regarding the random site of biopsy and the number of cells excised, the trisomy may not be observed. Additional reports and data including postpartum karyotype analysis of the newborns are necessary to provide conclusive decisions. The transfer of mosaic embryos marks a new era in ART and future studies and reports of cases are needed to help guide clinicians to make safe decisions regarding mosaic embryos.
Ideally, future studies would include analysis of more cells, such as placental tissue and skin cells in the postpartum period. PGT-A is widely used for a number of indications and with the introduction of NGS into the field and increased identification of mosaicism, clinicians require more informative data to guide them to make safe decisions when considering transfer of mosaic embryos. Meanwhile, clinicians are strongly advised to give comprehensive counseling to patients regarding the possible risks of mosaic embryo transfer, including true fetal mosaicism.
Semra Kahraman, Prof. Beril Yuksel, Assoc. Mesut Yesil, MSc. Caroline Pirkevi Cetinkaya, PhD: manuscript editing. National Center for Biotechnology Information , U. Hum Reprod. Published online Mar Author information Article notes Copyright and License information Disclaimer. Correspondence address. E-mail: moc. For commercial re-use, please contact journals. This article has been cited by other articles in PMC. Abstract Mosaic embryos have the potential to implant and develop into healthy babies.
Keywords: preimplantation genetic testing, mosaic embryo transfer, next-generation sequencing, true fetal mosaicism, baby with mosaicism. Introduction Chromosomal mosaicism is defined as two or more distinct cell lines within an embryo and is a relatively common finding in IVF-derived human embryos.
Case report Here we present the first report of a successful pregnancy and a healthy live birth with true fetal mosaicism of monosomy 2 after the transfer of an embryo with mosaic monosomy of chromosome 2. Open in a separate window. Figure 1.
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