China
Africa
Explore chapters and articles related to this topic
Genetics and metabolic disorders
Published in Jagdish M. Gupta, John Beveridge, MCQs in Paediatrics, 2020
Jagdish M. Gupta, John Beveridge
The pedigree is strongly suggestive of non-specific X-linked mental retardation. Specific cytogenetic studies have ruled out fragile X mental retardation as the underlying cause of the problem in these brothers. The risk to this girl's offspring is not increased by the fact that her mother gave birth to a child with non-disjunction trisomy 21. Pedigree information suggests the mother is a carrier of non-specific X-linked mental retardation. This then infers a 1 in 2 risk that her daughter is a carrier, which in turn implies a 1 in 8 risk to her offspring. If the affected retarded males have not shown karyotypic abnormalities (including fragile X), an analysis of the chromosomes of the pregnancy will not be useful in providing prenatal diagnosis.
Transfer of Mosaic Embryos
Published in Darren K. Griffin, Gary L. Harton, Preimplantation Genetic Testing, 2020
Francesco Fiorentino, Ermanno Greco, Maria Giulia Minasi, Francesca Spinella
Euploid/aneuploid mosaicism may occur by mitotic errors arising after fertilization of normal gametes. Conversely, it may originate as a meiotic non-disjunction event, leading to a trisomic conceptus, followed be a second post-zygotic event (trisomy rescue) [1,3–9] (Figure 9.1). Mitotic events that lead to mosaicism may include anaphase lag, mitotic nondisjunction, inadvertent chromosome demolition, or premature cell division before DNA duplication [6,10–12]. Some fluorescence in situ hybridization (FISH) studies suggest that mosaic embryos are the result of mitotic non-disjunction, with only 5% being due to other mechanisms, such as anaphase lag [13]. Subsequent studies using whole-genome hybridization and modern sequencing approaches have revealed that most of the diploid–aneuploid embryos are affected by single chromosome gains or losses or both [12,14,15] (Figure 9.2).
Klinefelter Syndrome
Published in Botros Rizk, Ashok Agarwal, Edmund S. Sabanegh, Male Infertility in Reproductive Medicine, 2019
Mark Johnson, Tarek M. A. Aly, Amr Abdel Raheem
About 80%–90% of KS patients have a 47,XXY karyotype among the cells, with the remaining 10%–20% having: 48,XXXY, 48,XXYY, 47,iXq,Y (structurally abnormal X chromosome, e.g., X isochromosome) karyotypes or mosaicisms of two different genetic lines such as 47,XXY/46,XY [7]. Nondisjunction, where the sex chromosomes fail to separate during oogenesis in meiosis I (50% of occurrences); or meiosis I (40% of occurrences) in spermatogenesis; or during oogenesis in meiosis II (10% of occurrences) and is thought to be the mechanism behind the additional X chromosome [8]. Less commonly (around 3%), nondisjunction occurs during early embryogenesis in the fertilized egg [7].
Breastfeeding Experiences of Mothers of Children with Down Syndrome
Published in Comprehensive Child and Adolescent Nursing, 2019
Rebeca Barros da Silva, Maria do Céu Barbieri-Figueiredo, Marcia Van Riper
Down syndrome (DS) or Trisomy 21 is a genetic disorder caused by the presence of extra chromosome 21 material. DS is the most common genetic cause of intellectual disability and affects 1/1000 newborns (WHO, 2016). Most cases of DS (over 95%) are due to Trisomy 21, which means each cell in the person’s body has three copies of chromosome 21 instead of the typical 2 copies. This type of DS is not inherited; it is due to a random error in cell division known as nondisjunction which results in a reproductive cell that includes an abnormal number of chromosomes. Children with DS often have distinctive phenotypic features, such as oblique palpebral fissures, prominent epicanthal folds, a flat facial profile, muscle hypotonia, hyperflexability, low set ears, an enlargement of the tongue in relationship to the size of their mouth, and clindactily of the fifth finger and sandal toes (Bull, 2011; Van Riper, 2016). While some of these features are likely to affect breastfeeding, others do not; many children with DS are able to breastfeed successfully (Bull, 2011; The Canadian Syndrome Society, 2010). Children with DS who are most likely to have difficulty with breastfeeding are those with congenital heart defects and those with low birth weights or growth retardation.
Genotoxic and mutagenic studies of teratogens in developing rat and mouse
Published in Drug and Chemical Toxicology, 2019
Eyyüp Rencüzoğulları, Muhsin Aydın
Teratogens are defined as agents that cause congenital defects. The effects of these agents depend on the time of exposure of the pregnant women, the dose of the medicine, the duration of the drug exposure, and the genetic susceptibility of the person. In Environment and Birth Defects book, which was published by James G. Wilson in 1973, it was stated that chemicals kill the embryo when taken in the early embryonic period and causes structural abnormalities in the embryogenesis period (Wilson, 1973). In the same book, Wilson stated that all mutagens could not be teratogenic, but the mechanisms of teratogenesis was listed as follows: (a) mutation, (b) chromosomal breaks or nondisjunction, (c) miotic interference, (d) altered nucleic acid integrity or function, (e) lack of precursors, (f) altered energy sources, (g) enzyme inhibition, (h) fluid-osmolyte imbalance, and (i) changed membrane characteristics. This suggests that genotoxic and mutagenic agents may also be teratogenic (el-Ashmawy et al. 2011, Shreder et al. 2011, Murkunde et al. 2012, El-Shershaby et al. 2014, Carvalho et al. 2016). Similarly, Wedebye et al. (2015) reported that the germline mutations were reproductive toxic.
The futile case of the aging ovary: is it mission impossible? A focused review
Published in Climacteric, 2018
Several studies are trying to attempt the isolation of mitotic germ cells from adult human ovaries50. Virant-Klun and colleagues50 have tried to isolate the putative ovarian stem cells (OSCs) from the ovarian surface and follicles. OSC scrapings yielded isolated small round cells, 2–4 µm in diameter which were then cultured; some oocyte-like cells developed and reached 20 µm in diameter. They were termed ‘embryonic-like stem cells of the adult’ and these oocyte-like cells underwent parthenogenetic activation to form blastocyst-like structures. Experimental biological research is being carried out towards development of artificial gametes from diploid somatic cells but the efficacy, safety and functionality of artificial gametes are still under question. The greatest hurdle being faced is the inability of the somatic cells to reduce their chromosomes with the requisite fidelity and efficacy of a germ cell, which leads to a high incidence of chromosomal abnormalities resulting from non-disjunction. Artificial gametes, generated by manipulation of their progenitor or stem cells, could potentially end infertility. In animals, artificial sperm and oocytes from germline stem cells, embryonic stem cells and induced pluripotent stem cells have resulted in the birth of viable offspring. In humans, artificial sperm have been generated from embryonic stem cells and induced pluripotent stem cells. Artificial human oocytes have been generated from germline stem cells, embryonic stem cells and somatic cells. However, normal developmental potential, genetic stability and live births have not been reported following the use of human artificial gametes51.