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The Scientific Basis of Medicine
Published in John S. Axford, Chris A. O'Callaghan, Medicine for Finals and Beyond, 2023
Chris O'Callaghan, Rachel Allen
The main cause of chromosomal structural abnormality is double-stranded DNA breakage. DNA breakage occurs as a natural feature of meiosis, but can also be triggered by ionizing radiation. Broken ends of DNA are rapidly repaired by specific enzymes. Abnormal repair generates structural abnormalities including translocations, deletions, duplications and inversions of DNA segments. Translocations represent a transfer of DNA between two chromosomes. This exchange does not necessarily result in loss of DNA, so an individual carrier may remain healthy. However, chromosome translocations can interfere with meiosis such that offspring cells may receive a partial trisomy or monosomy. Deletions result in a loss of genetic material, often spanning many genes. Their effects can be severe, resulting in congenital malformation. Duplications of a DNA stretch are generally less harmful than deletions. Introduction of two separate double-stranded breaks can generate an inversion if the chromosomal fragment is reinserted in a back-to-front orientation. Although no DNA is lost or gained in this process, inversions can obstruct chromosome pairing during meiosis.
Heterologous Pairing and Fertility in Humans
Published in Christopher B. Gillies, Fertility and Chromosome Pairing: Recent Studies in Plants and Animals, 2020
Chromosome pairing begins in most species with the rough alignment (300 nm apart) of the lateral elements of the homologous chromosomes.17 Only when lateral elements are separated by approximately 100 nm does the SC begin to form. Initiation points may be numerous, as in plant species, or be almost strictly telomeric, as in the human oocyte. Normally, only homologs will initiate synapsis at meiotic prophase (homologous pairing), but numerous examples now exist of SCs that can form between chromosomes or segments of chromosomes that are nonhomologous in genetic content (heterologous pairing).18–20 Heterologous pairing may also develop at prophase, in chromosomal rearrangements such as duplications or inversions,21 and has been termed by Moses et al.22 “synaptic adjustment”. The fact that such SCs appear of normal dimensions and structure suggests that the SC, per se, is not the mechanism of genetic exchange, as such heterologous pairing in plant haploid species,23 does not lead to chiasma formation or crossing over.
Endocrine and reproductive disorders
Published in Angus Clarke, Alex Murray, Julian Sampson, Harper's Practical Genetic Counselling, 2019
Disorders of sperm production include primary sex chromosome disorders such as XXY (Klinefelter) syndrome, other disorders affecting the testis (e.g. myotonic dystrophy), balanced chromosomal translocations causing abnormalities of chromosome pairing in meiosis, clinical defects affecting sperm motility, and a variety of poorly defined biochemical disorders. Molecular deletions of the Y chromosome involving the azoospermic factor AZF are an important cause. Blockage or aplasia of the vas deferens causes infertility in most males affected by cystic fibrosis or carrying the condition in one copy of the CFTR gene along with otherwise benign variants in their other copy of the same gene. A mild form of this may be responsible for some apparently primary cases of such obstruction.
Genetic variations as molecular diagnostic factors for idiopathic male infertility: current knowledge and future perspectives
Published in Expert Review of Molecular Diagnostics, 2021
Mohammad Karimian, Leila Parvaresh, Mohaddeseh Behjati
The synaptonemal complex is an important component for chromosome pairing, segregation, and recombination. Hormad1 is essential for mammalian gametogenesis because male knockout mice are infertile. Hormad1-deficient testes in the early stages of pachytene show meiosis arrest without demonstration of synaptonemal complexes [152]. To analyze the hypothesis that human HORMAD1 gene defect is associated with human azoospermia induced by meiosis arrest, mutation analysis in all coding regions was performed by Miyamoto et al. By sequence analysis, SNP1 (163A> G), SNP2 (501T>G) and SNP3 (918C>T) were found in exons 3, 8, and 10. Both SNP1 and SNP2 were associated with human azoospermia resulting from the complete arrest of primary meiosis. They suggested that HORMAD1 has an essential mitotic function in human spermatogenesis [153].
Identification of potential prognostic biomarkers in vulval squamous cell carcinoma based on human papillomavirus infection Status-Analysis of GSE183454
Published in Journal of Obstetrics and Gynaecology, 2023
Ruxing Xi, Donghong Li, Shuanque Yang, Hui Zhang, Lijuan Hu, Xiaowei Wang, Guoqing Wang, Yan Wang
We determined a sub-network module with significant prognostic values, of these, with high degree of connectivity were selected as key molecules. As shown in Figure 2(A), SYCP2, SMC1B, RNF212, MAJIN and C14orf39 were selected and significantly related with synaptonemal complex, homologous chromosome pairing at meiosis, homologous chromosome segregation, meiotic chromosome segregation and chromosome organisation involved in meiotic cell cycle, respectively. We also investigated the protein correlation between these key molecules, as shown in Figure 2(B), SYCP2, SMC1B, RNF212, MAJIN and C14orf39 were all significantly related with each other.
Clinical aspects of infertile 47,XYY patients: a retrospective study
Published in Human Fertility, 2019
Parnaz Borjian Boroujeni, Marjan Sabbaghian, Ahmad Vosough Dizaji, Shabnam Zarei Moradi, Navid Almadani, Faranak Mohammadpour Lashkari, Mohamad Reza Zamanian, Anahita Mohseni Meybodi
The variation of fertility status between 47,XYY men could be due to differences in the rate, or the time, at which cells lose the extra Y chromosome spontaneously and form clones of normal cells which can decolonize the testis (Abdel‐Razic et al., 2012; Faed et al., 1976). In other words, the presence of the additional Y chromosome may result in abnormal chromosome pairing, disrupt the completion of spermatogenesis and result in severe oligoasthenozoospermia (Abdel‐Razic et al., 2012; Gabriel-Robez et al., 1996; Wong et al., 2008).