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Genetic Counseling in Assisted Reproductive Technology
Published in Carlos Simón, Carmen Rubio, Handbook of Genetic Diagnostic Technologies in Reproductive Medicine, 2022
X-linked inheritance is when a disease-associated mutation occurs on the X chromosome. Males are generally more severely affected than females. Some X-linked conditions are so severe in males that they are lethal. Some X-linked conditions are considered dominant, and some are considered recessive. Regardless of dominant or recessive classification, the severity of symptoms in females varies widely, depending on which of the two X chromosomes become inactivated. When a female is a carrier of an X-linked condition, there is a 50% chance of passing on the variant. Daughters who inherit the variant would also be carriers, and sons who inherit the variant would be affected. Affected males would pass on the variant along with the X chromosome to all daughters, who would therefore be carriers, and would pass on the Y chromosome to all sons, who would therefore be unaffected.
Clinical Cancer Genetics
Published in Pat Price, Karol Sikora, Treatment of Cancer, 2020
Rosalind A. Eeles, Lisa J. Walker
In X-linked inheritance the mutated gene is carried on the X-chromosome. Females have two X-chromosomes, and can therefore be carriers of the condition, but are not usually affected by it. As males only have one copy of the X chromosome, if they inherit a mutated gene on the X from their mother, they will inherit the condition. A carrier female would therefore have a 50 per cent chance of passing the condition on to each of her sons, and a 50 per cent chance that her daughters would, themselves, be carriers. The best-known example of this mode of inheritance outside cancer is Duchenne muscular dystrophy, but X-linked familial prostate cancer has also been observed in a small number of families, although the exact gene has not yet been identified.
Sex Chromosome Pairing and Fertility in the Heterogametic Sex of Mammals and Birds
Published in Christopher B. Gillies, Fertility and Chromosome Pairing: Recent Studies in Plants and Animals, 2020
Differentiated sex chromosomes originate from an ancestral, autosomal pair.23 During the evolutionary process, segments of the original autosomes may remain relatively unchanged, thus constituting “relics” of the ancestral pair. If sex chromosomes have a pairing region, it seems reasonable to assume that this region is (or contains) the relics of the ancestral pair.2 However, this is not always true in mammals, as shown by some hamsters and deer mice (see Section V). The evolution of sex chromosomes is assumed to proceed towards the conversion of “homologous” regions into “differential” regions,1 the latter sharing little or no genetic content. Again, this is far from being proved. The Y member of the sex pair is generally reduced in size, while the X remains constant.24 In mammals, the X chromosome is extensively conserved, as shown by cytological as well as biochemical criteria.24,25 In mammals, the “original” (conserved) X chromosome amounts to 5 to 5.6% of the homogametic haploid set,26 while the “original” Z chromosome of birds amounts to 7.2 to 9.3% of the haploid genome.27 The reasons for the evolutionary conservation of the X (or Z) chromosome are not well understood;28 they could be related to the widespread sterility of X-autosome translocations in mammals.28 However, Z-autosome translocations do not result in gametogenic impairment (see Section IX) and, thus, the negative selection against these rearrangements cannot explain the “conservation” of the Z chromosome.
Clinical characteristics of high myopia in female carriers of pathogenic RPGR mutations: a case series and review of the literature
Published in Ophthalmic Genetics, 2023
Matthew Tran, Masha Kolesnikova, Angela H. Kim, Tia Kowal, Ke Ning, Vinit B. Mahajan, Stephen H. Tsang, Yang Sun
The classic model of X-linked inheritance holds that pathogenic mutations in genes on the X-chromosome produce a phenotype solely or primarily in hemizygous males, while heterozygous females usually have no disease or manifest much less severe disease than males with the same variant (17). However, a recent cohort study of 125 heterozygous female RPGR mutation carriers described a wide spectrum of phenotypes ranging from asymptomatic to severe retinal degeneration, demonstrating that female carriers of XLRP can also suffer from visual dysfunction (9). Specifically, myopia was observed in 73% of heterozygotes, and complete expression of the RP phenotype was observed in 23% carriers (9). Interestingly, others have reported a distinctive X-linked genotype-phenotype correlation between RP and pathological myopia characterized by the symmetrical presence of disease in both retinas of all heterozygous female carriers, suggesting that some RPGR variants are highly penetrant and may underlie both RP and myopia (8,18,19). With novel upcoming therapeutic options including gene therapy and optogenetic strategies now being explored in Phase I/II clinical trials for the treatment of XLRP, the phenotypic characterization of RPGR mutations in females has gained importance (20–22). Here, we report the clinical and genetic findings of four non-consanguineous and unrelated female patients with pathogenic RPGR variants and concomitant high myopia (Table 1).
Prevalence and development of aortic dilation and dissection in women with Turner syndrome: a systematic review and meta-analysis
Published in Expert Review of Cardiovascular Therapy, 2023
F. Meccanici, J.W.C. de Bruijn, J.S. Dommisse, J.J.M. Takkenberg, A.E. van den Bosch, J. W. Roos-Hesselink
Turner syndrome (TS) affects women with either an absent or incomplete X-chromosome. The incidence of TS among live-born females is approximately 1:2500 [1,2]. Some typical features include short stature, gonadal dysgenesis, and cardiovascular disease [3]. Common congenital cardiac defects include bicuspid aortic valve (BAV), aortic coarctation (COA), abnormal pulmonary venous return, aortic dilatation, and dissection [4–6]. Alarming case reports published on aortic dissection in women with TS at the end of the 20th century [7–10] led to more awareness and research on aortic disease in this patient group. As a result, the guidelines now recommend lifelong close monitoring of women with TS to prevent aortic complications [11]. However, there might be a bias in the published literature, especially on the topic of aortic dissection. Most studies concern case reports or retrospective series, highlighting the patients with an event, thus the exact burden of aortic disease in women with TS is unclear.
Is chronic pain as an autoimmune disease?
Published in Canadian Journal of Pain, 2022
If the neurons associated with nociceptive responses turn out not to be the fundamental source accounting for sexual dimorphisms in unresolved pain states and major sex differences associated with human pathologies cannot solely be explained by environmental factors or reproductive hormones, another difference between males and females is responsible for the chronic nature of pain. X and Y chromosome–associated genes exhibit differential expression profiles. This arises independent of an individual’s hormonal status and could therefore represent a major driver for the differences between females and males in pathological conditions, including chronic pain. Identification and characterization of genes on the X and Y chromosomes are being actively investigated. The X chromosome represents approximately 2.5% in men (XY) of the total DNA within each cell, referred to as the dosage, which is doubled in women (XX).