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Mosaicism in Preimplantation Embryos
Published in Carlos Simón, Carmen Rubio, Handbook of Genetic Diagnostic Technologies in Reproductive Medicine, 2022
Maurizio Poli, Antonio Capalbo
Mosaicism is defined as the presence of two or more genotypically different cell lines in a given organism, embryo, or cell line. Chromosomal imbalances present in all cells of an organism are defined as uniform aneuploidies and mostly derive from aberrant meiotic processes occurring during the final stages of oocyte maturation (1–3). Differently, embryo mosaicism originates from mitotic segregation errors occurring in post-zygotic developmental stages when progenitor cells sequentially divide into daughter cells. These defective events can occur in either euploid or aneuploid conceptuses (4).
Prenatal Diagnosis and Screening for Aneuploidy
Published in Vincenzo Berghella, Obstetric Evidence Based Guidelines, 2022
Sarah Harris, Angie Jelin, Neeta Vora
The presence of a single X chromosome or any karyotype with Xp missing, such as isochromosome Xq, ring X, or deletion Xp. The presence of a single X chromosome results from chromosomal nondisjunction. Mosaicism is common (40%) and may include a 46,XY karyotype associated with ambiguous genitalia. Since features of Turner syndrome are seen in other syndromes, karyotype is essential to make the diagnosis. Chromosome studies on more than one tissue may be needed to detect mosaicism. Not associated with advanced maternal age.
Mosaicism Mechanisms in Preimplantation Embryos
Published in Darren K. Griffin, Gary L. Harton, Preimplantation Genetic Testing, 2020
Maurizio Poli, Antonio Capalbo
Mosaicism is defined as the presence of two or more genotypically different cell lines in a given organism, embryo, or cell line. Uniform aneuploidies mostly derive from aberrant meiotic processes [1–3]. However, embryo mosaicism can originate from mitotic segregation errors in post-zygotic developmental stages of a euploid or aneuploid conceptus [4].
Spectrum and tissue distribution of RB1 pathogenic alleles in mosaic retinoblastoma patients
Published in Ophthalmic Genetics, 2022
Yan Zhang, Wen-Bin Wei, Junyang Zhao, Xiaolin Xu, Fufeng Wang
The correlation between mosaicism level and heritability risk is important. Following primordial germ cell (PGC) differentiation embryonic cells are restricted to either somatic or germ tissues. Variant alleles occurring before this developmental period can be present in both types of tissues (8). The abundance of mutant somatic cells may reflect the timing of variant allele occurrence and potentially predict the risk for a variant allele to be transmitted to the offspring. Rushow et al. reported eight mosaics with RB1 variant alleles at levels ranging from 5% to 25% who were followed until child-bearing age. Three had children or a fetus who carried their RB1 variant alleles. The lowest level of mosaicism among those three parents was 7.5%. However, another patient with RB1 variant allele (c.763C>T) was detected to have 7.5% mutant DNA in blood but no variant allele in his sperm (7). Due to the interplay of multiple factors mosaicism levels are not necessarily proportional to heritability risk. It is important to note that in pure germline mosaicism the variant alleles may be transmitted to offspring but not detectable in blood. A sufficient number of adults who are mosaic for RB1 variant alleles is necessary in order to correlate the percentage of mosaicism with the probability of having affected offspring or positive mosaicism in sperm (i.e. germline mosaicism). However, there appears to be no clear-cut demarcation to distinguish between somatic and germline mosaicism.
Neuropsychological and Social Characteristics of a 7 Year Old Child with Hypomelanosis of Ito Followed for 11 Years
Published in Developmental Neuropsychology, 2022
George P. Prigatano, Alexandra Novak, Vinodh Narayanan
Hypomelanosis of Ito (HI) “is a neurocutaneous disorder with hypopigmented lesions following the lines of Blaschko” (Ream, 2015, p. 281). The single genetic etiology of this condition has not been defined, but there has been an association with chromosomal mosaicism. “Mosaicism occurs when there are two different populations of cells during embryologic development, often due to mutation or chromosomal nondisjunction in one cell line” (Ream, 2015, p. 286). While skin hypopigmentation is the most prominent feature of HI, this clinical condition is often associated with a variety of musculoskeletal and central nervous system abnormalities. While the neuropsychological and neurobehavioral symptoms of these children can be variable (e.g., attentional disturbances, autism, Asperger’s syndrome, developmental delays, and poorly defined learning disorders (Kumar, Radhakrishnan, Chowdhary, & Giampietro, 2001; Pavone, Praticò, Ruggieri, & Falsaperla, 2015)), delays in speech production and reduced intellectual ability are commonly reported (Ruggieri & Pavone, 2000). Esquivel, Pitt, and Boyd (1991) have also reported that many children with HI have seizures during early childhood without a common pattern of abnormal rhythmic EEG findings.
Noninvasive prenatal screening in southeast China: clinical application and accuracy evaluation
Published in Expert Review of Molecular Diagnostics, 2022
Li Wen, Jiye Gao, Leilei Huang, Dongmei Li, Guansheng Zhong
It is agreed that karyotyping is one of the most common methods for validating positive NIPS results followed by CMA [35–37]. In our study, we found that many pregnant women with high-risk NIPS results chose karyotyping and CMA for further confirmation. In some cases, additional findings occurred, which might increase the complexity of clinical consultation and even cause anxiety during pregnancy. Of 15 NIPS cases positive with microdeletion/microduplication findings, 66.7% (10/15) selected to test with parental peripheral blood. And the majority of them (90%, 9/10) proved to be either maternal or paternal inherited, while case 15 was classified as De novo. Furthermore, mosaicism in the sex chromosome was frequently seen in our study, accounting for 24.8% (28/113) of cases, which were confirmed with sex chromosome abnormalities. Although FISH has an outstanding performance in detecting chromosomal mosaicism without cell culture, inconsistent with Jing et al.’s study, we discovered a high proportion of 45,X mosaicism by the application of karyotyping and CMA. Anyway, accurate recognition of fetal mosaicism has vital importance in guiding after-test counseling.