Chromosome disorders

Xem 1-20 trên 22 kết quả Chromosome disorders
  • Maternal Age and Trisomy The association between increasing maternal age and trisomy is the most important etiologic factor in congenital chromosomal disorders. Among women under the age of 25, ~2% of all clinically recognized pregnancies are trisomic; by the age of 36, however, this figure increases to 10% and by the age of 42, to 33% (Fig. 63-5). This association between maternal age and trisomy is exerted without respect to race, geography, or socioeconomic factors and likely affects segregation of all chromosomes.

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  • Applications of FISH The majority of FISH applications involve hybridization of one or two probes of interest as an adjunctive procedure to conventional chromosomal banding techniques. In this regard, FISH can be utilized to identify specific chromosomes, characterize de novo duplications or deletions, and clarify subtle chromosomal rearrangements. Its greatest utilization, however, is in the detection of microdeletions (see below). Though conventional cytogenetic studies can detect some microdeletions, initial detection and/or confirmation with FISH is essential.

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  • Molecular Cytogenetics The introduction of FISH methodologies in the late 1980s revolutionized the field of cytogenetics. In principle, FISH is similar to other DNA-DNA hybridization methodologies. The probe is labeled with a hapten, such as biotin or digoxigenin, to allow detection with a fluorophore (e.g., FITC or rhodamine). After the hybridization step, the specimen is counter-stained and the preparations are visualized with a fluorescence microscope.

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  • Cytogenetic Testing in Prenatal Diagnosis The vast majority of prenatal diagnostic studies are performed to rule out a chromosomal abnormality, but cells may also be propagated for biochemical studies or molecular analyses of DNA. Three procedures are used to obtain samples for prenatal diagnosis: amniocentesis, chorionic villus sampling (CVS), and fetal blood sampling. Amniocentesis is the most common procedure and is routinely performed at 15–17 weeks of gestation.

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  • Chromosome segregation in meiosis. A. In meiosis I, each of the 23 pairs of chromosomes finds its "partner," or homologue, and exchanges genetic material (recombines) with it. At metaphase, each homologous pair aligns on the equatorial plate; at anaphase, each member of the homologous pair segregates from its partner. Thus, at the end of meiosis I, each daughter cell contains 23 chromosomes, with each chromosome consisting of two sister chromatids. B. In meiosis II, each chromosome aligns on the metaphase plate, and at anaphase, each of the two sister chromatids divides from the other.

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  • Microdeletion Syndromes The term contiguous gene syndrome refers to genetic disorders that mimic a combination of single-gene disorders. They result from the deletion of a small number of tightly clustered genes. Because some are too small to be detected cytogenetically, they are termed microdeletions. The application of molecular techniques has led to the identification of at least 18 of these microdeletion syndromes (Table 63-4). Some of the more common ones include the Wilms' tumor–aniridia complex (WAGR), Miller Dieker syndrome (MDS), and velocardiofacial (VCF) syndrome.

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  • Deletions involving the long arm of chromosome 22 (22q11) are the most common microdeletions identified to date, present in ~1/3000 newborns. VCF syndrome, the most commonly associated syndrome, consists of learning disabilities or mild mental retardation, palatal defects, a hypoplastic aloe nasi and long nose, and congenital heart defects (conotruncal defect).

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  • Readable, well organized, and easy to use, this outstanding encyclopedia signifies a timely and major advance in providing in-depth and comprehensive coverage of medical genetics for the lay reader. The two volumes include nearly 400 substantive entries on genetic diseases and conditions as well as information on basic genetics concepts such as DNA, chromosomes, genetic testing, and pedigree analysis and construction (genetic family history).

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  • In humans, the normal diploid number of chromosomes is 46, consisting of 22 pairs of autosomal chromosomes (numbered 1–22 in decreasing size) and one pair of sex chromosomes (XX in females and XY in males). The genome is estimated to contain between 30,000 and 40,000 genes. Even the smallest autosome contains between 200 and 300 genes. Not surprisingly, duplications or deletions of chromosomes, or even small chromosome segments, have profound consequences on normal gene expression, leading to severe developmental and physiologic abnormalities. ...

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  • I wrote the first edition of this book more than 20 years ago, and the discoveries in genetics since then have been phenomenal. The new knowledge and applications of human genetics to health and to society have made it even more necessary that nurses "think genetically" in their practice and, indeed in their lives. Genetic factors can be responsible in some way for both direct and indirect disease causation; for variation that determines predisposition, susceptibility, and resistance to disease and also for response to therapeutic management.

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  • This chapter include objectives: Evaluate the effects of continuous variation, pleiotropic genes, lack of complete dominance, environmental modifications of genes, and epistasis on disease; understand the importance of crossing over in terms of gene assortment and construction of genetic maps; describe the many genetic disorders discussed in the text, their symptoms, relative frequency in specialized populations, and their genetic basis;...

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  • The programme is indebted to the five hundred plus international nurses from twentythree different countries who have worked and studied with us over the last four years at the Oxford Radcliffe Hospitals NHS Trust, the University Hospitals of Leicester NHS Trust and other hospitals. They have tested our new ideas, suggested improvements and shown honesty, courage and a sense of humour throughout. We are particularly grateful to the international nurses who commented on the first drafts of this book....

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  • Uncovering Recurrent Submicroscopic Rearrangements As a Cause of Disease For five decades since Fred Sanger's (1) seminal discovery that proteins have a specific structure, since Linus Pauling's (2) discovery that hemoglobin from patients with sickle cell anemia is molecularly distinct, and since Watson and Crick's (3) elucidation of the chemical basis of heredity, the molecular basis of disease has been addressed in the context of how mutations affect the structure, function, or regulation of a gene or its protein product.

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  • Harrison's Internal Medicine Chapter 64. The Practice of Genetics in Clinical Medicine Implications of Molecular Genetics for Internal Medicine The field of medical genetics has traditionally focused on chromosomal abnormalities (Chap. 63) and Mendelian disorders (Chap. 62). However, there is genetic susceptibility to many common adult-onset diseases, including atherosclerosis, cardiac disorders, asthma, hypertension, autoimmune diseases, diabetes mellitus, macular degeneration, Alzheimer's disease, psychiatric disorders, and many forms of cancer.

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  • While most autosomal dominant inherited cancer syndromes are due to mutations in tumor-suppressor genes (Table 79-1), there are a few interesting exceptions. Multiple endocrine neoplasia type II, a dominant disorder characterized by pituitary adenomas, medullary carcinoma of the thyroid, and (in some pedigrees) pheochromocytoma, is due to gain-of-function mutations in the protooncogene RET on chromosome 10. Similarly, gain-of-function mutations in the tyrosine kinase domain of the MET oncogene lead to hereditary papillary renal carcinoma.

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  • This book provides recent developments and advances in research on Down syndrome. It covers a wide range of topics, including investigations on prenatal diagnosis and screening, genetic counseling, neoplastic disease, congenital heart disease, dentistry and oral health, obesity, molecular genetics and neurological disorders in Down syn‐ drome. It is also a resource for scientists and research workers who wish to learn more about Down syndrome. To date, well over one hundred chromosome syndromes have been reported. Whilst on an individual basis many of these are...

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  • The etiology of PV is unknown. Although nonrandom chromosome abnormalities such as 20q, trisomy 8, and especially 9p, have been documented in up to 30% of untreated PV patients, unlike CML no consistent cytogenetic abnormality has been associated with the disorder. However, a mutation in the autoinhibitory, pseudokinase domain of the tyrosine kinase JAK2—which replaces valine with phenylalanine (V617F), causing constitutive activation of the kinase— appears to have a central role in the pathogenesis of PV.

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  • Parkinson’s disease is the second most common neurodegenerative disorder. The pathological hallmark of the disease is degeneration of midbrain dopaminergic neurons. Genetic association studies have linked 13 human chromosomal loci to Parkinson’s disease. Identification of gene(s), as part of the etiology of Parkinson’s disease, within the large number of genes residing in these loci can be achieved through several approaches, including screening methods, and considering appropriate criteria.

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  • The field of medical genetics has traditionally focused on chromosomal abnormalities (Chap. 63) and Mendelian disorders (Chap. 62). However, there is genetic susceptibility to many common adult-onset diseases, including atherosclerosis, cardiac disorders, asthma, hypertension, autoimmune diseases, diabetes mellitus, macular degeneration, Alzheimer's disease, psychiatric disorders, and many forms of cancer.

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  • Idiopathic Parkinson’s disease (PD) is an age-dependent, neurodegenerative disorder and is predominantly sporadic. Only 20–30% of patients have a positive family history for PD with a complex mode of inheritance. In a few extended families, the disease is inherited as an autosomal dominant trait. Linkage to chromosome 4 was reported in a large Italian kindred multiply affected by an early-onset form of PD (1). However, this finding was not replicated in a sample of 94 Caucasian families by Scott et al. (2), or in 13 multigenerational families by Gasser et al. (3)....

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