Genetic Disorders

5 Key excerpts on "Genetic Disorders"

• 

  eBook - ePub

  New Thinking About Genetics

  • Britannica Educational Publishing, Kara Rogers(Authors)
  • 2010(Publication Date)
  • Britannica Educational Publishing

    (Publisher)

  ENETIC DISEASES OF HUMANS

  W ith the increasing ability to control infectious and nutritional diseases in developed countries, there has come the realization that genetic diseases are a major cause of disability, death, and human tragedy. Rare, indeed, is the family that is entirely free of any known genetic disorder.

  Many thousands of different Genetic Disorders with defined clinical symptoms have been identified. Of the 3 to 6 percent of newborns with a recognized birth defect, at least half involve a predominantly genetic contribution. Furthermore, genetic defects are the major known cause of pregnancy loss in developed countries, and almost half of all spontaneous abortions (miscarriages) involve a chromosomally abnormal fetus. About 30 percent of all postnatal infant mortality in developed countries is due to genetic disease, and about 30 percent of pediatric and 10 percent of adult hospital admissions can be traced to a predominantly genetic cause. Finally, medical investigators estimate that genetic defects—however minor—are present in at least 10 percent of all adults. Thus, these are not rare events.

  A congenital defect is any biochemical, functional, or structural abnormality that originates prior to or shortly after birth. It must be emphasized that birth defects do not all have the same basis, and it is even possible for apparently identical defects in different individuals to reflect different underlying causes. Though the genetic and biochemical bases for most recognized defects are still uncertain, it is evident that many of these disorders result from a combination of genetic and environmental factors.

  CLASSES OF GENETIC DISEASE

  Most human genetic defects can be categorized as resulting from either chromosomal, single-gene Mendelian, single-gene non-Mendelian, or multifactorial causes.

  DISEASES CAUSED BY CHROMOSOMAL ABERRATIONS

  About 1 out of 150 live newborns has a detectable chromosomal abnormality. Yet even this high incidence represents only a small fraction of chromosome mutations since the vast majority are lethal and result in prenatal death or stillbirth. Indeed, 50 percent of all first-trimester miscarriages and 20 percent of all second-trimester miscarriages are estimated to involve a chromosomally abnormal fetus.

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  eBook - ePub

  Handbook of Pediatric Psychology in School Settings

  • Ronald T. Brown(Author)
  • 2003(Publication Date)
  • Routledge

    (Publisher)

  PART IV: Developmental Disorders and Conditions

  Passage contains an image

  20 Genetic Disorders in Children

  LeAdelle Phelps

  State University of New York at Buffalo

  OVERVIEW

  More than 200 genes have been identified as causing hereditary diseases; new genes are isolated at a rate of 1 per month (Singer & Berg, 1997; Thompson, Hellack, Braver, & Durica, 1997). Some childhood disorders originate solely from prenatal or postnatal environmental events (e.g., deaf-blindness in the offspring caused by the pregnant mother contracting rubella, exposure to toxic chemicals such as PCBs [polychlorinated biphenyls], or sustainment of a traumatic head injury) but many are clearly related to a defective gene transmitted through the generations (e.g., albinism, hemophilia, sickle cell anemia, Tay-Sachs). Still other conditions appear to result from genetic susceptibility coupled with prenatal or postnatal stressors (e.g., stuttering, Giles de la Tourette’s syndrome). To facilitate an understanding of genetic conveyance, principles of hereditary transmission are presented and illustrated. A glossary is provided at the end of the chapter to facilitate an understanding of common genetic terms.

  There are 23 pairs of human chromosomes; 22 are autosomes (non-sex related) and the 23rd pair determines sex (XX for female, XY for male). All of the chromosomes, with the exception of the male-determining Y, contain thousands of genes that are the basic units of heredity. Each gene consists of chemicals called nucleotides, which are designated by the letters A (adenine), C (cytosine), G (guanine), and T (thymine). The sequence of these nucleotides determines which specific protein is produced. Initial changes in the normal sequence of the nucleotides occur through sudden spontaneous mutations. The outcomes may be deletions, alterations, or faulty repetitions of the A, C, G, and T sequence, thus modifying the intended protein. This transformed protein causes the appearance of clustered symptoms that define a specific disorder or syndrome.

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  eBook - ePub

  Berman's Pediatric Decision Making E-Book

  Expert Consult - Online and Print

  • Lalit Bajaj, Simon Hambidge, Ann-Christine Nyquist, Gwendolyn Kerby(Authors)
  • 2011(Publication Date)
  • Mosby

    (Publisher)

  Metabolic and Genetic Disorders Passage contains an image Evaluation for a genetic disease

  Gunter H. Scharer, MD

  Before birth and throughout life, genetic factors can cause or contribute to problems of growth, development, cognition, behavior, and general well-being. Knowledge of Genetic Disorders (single-gene defects), genomic imbalances (copy number variations), and abnormalities in gene regulation and gene interaction (epigenetics) plays an ever bigger role in modern medicine. Based on the correct diagnosis, potential complications can be recognized earlier and treated more effectively, adverse effects of existing and new treatments can be minimized, supportive therapies are optimized, and the prognosis for the individual may be predicted more accurately.

  Although correct numbers vary, it is estimated that between 30% and 50% of all admissions to pediatric hospitals occur because of congenital malformations present at birth, or less obvious genetic causes including the contributions of an underlying genetic disorder to the patient’s clinical presentation. Although our understanding of genetics and genetic disease mechanisms does increase rapidly, it will remain incomplete for the foreseeable future. Therefore, we have to rely not only on the results of an increasing number of diagnostic tools, but on the traditional clinical expertise of a dysmorphologist and the critical observations of the bedside clinician–researcher.

  The more classic genetic diseases (major chromosome abnormalities, Mendelian or single-gene disorders) often have a recognizable pattern of prenatal/postnatal growth retardation (including abnormal head size), motor/cognitive delays, muscular hypotonia/hypertonia, and other unique physical features (dysmorphisms). Recognition of specific patterns of multiple birth defects (congenital anomalies) may aid in the diagnosis of the genetic syndrome; however, the majority of birth defects are caused by “multifactorial” interaction of genes and environmental factors.

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  eBook - ePub

  Illustrated Textbook of Paediatrics E-Book

  • Tom Lissauer, Will Carroll, Tom Lissauer, Will Carroll(Authors)
  • 2021(Publication Date)
  • Elsevier

    (Publisher)

  Figure 9.1 Ensembl genome browser. The image shows part of chromosome region 22q11, involved in 22q11 deletion syndrome (DiGeorge syndrome). Although only part of the commonly deleted region is shown, the image shows several genes that are deleted in 22q11 deletion syndrome. The online Ensembl browser can be used to ‘zoom in’ on specific areas, showing the genes present in different chromosome regions, and can also be used to show the gene sequence itself.

  Genetic Disorders are:

  • • common, with 2% of live-born babies having a significant congenital anomaly and about 5% a genetic disorder
  • • burdensome to the affected individual, family, and society, as many are associated with severe and permanent disability.

  Genetically determined diseases include those resulting from:

  • • chromosomal abnormalities
  • • the action of a single gene (Mendelian disorders)
  • • unusual genetic mechanisms, such as imprinting
  • • interaction of genetic and environmental factors (polygenic, multifactorial, or complex disorders), which include epigenetic influences on gene expression from early in life.

  Chromosomal abnormalities

  Genes are composed of DNA that is wound around a core of histone proteins and packaged into a succession of supercoils to form chromosomes. The human chromosome complement was confirmed as 46 in 1956. The chromosomal abnormalities in Down, Klinefelter, and Turner syndromes were recognized in 1959, and thousands of chromosome defects have now been described.

  Chromosomal abnormalities are either numerical or structural. They occur in approximately 10% of spermatozoa and 25% of mature oocytes and are a common cause of early spontaneous miscarriage. The estimated incidence of chromosomal abnormalities in live-born infants is about 1 in 150. They often cause multiple congenital anomalies and cognitive difficulties. Acquired chromosomal changes play a significant role in carcinogenesis and tumour progression.

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  Diseases and Disorders in Infancy and Early Childhood

  • Janette B. Benson, Marshall M. Haith(Authors)
  • 2009(Publication Date)
  • Academic Press

    (Publisher)

  Science 193: 547–555. Relevant Website http://www.ncbi.nlm.nih.gov – Online Mendelian Inheritance in Man (OMIM). Genetic Disorders: Single Gene E L Grigorenko, Yale University, New Haven, CT, USA ã 2008 Elsevier Inc. All rights reserved. Glossary Developmental science – Studies of complex systemic changes in human occurring over life-span. Epigenetics – Studies of changes in gene functioning (silencing and transcription initiation) that occur without changes in the genes themselves. Genetics – Studies of heredity investigating how genes are transmitted from generation to generation. Genomics – Studies of the whole genome and how it functions as a complex system of interacting genes in an environment. Proteomics – Studies of proteins and their functions. Introduction We refer to development as a complex process of realiza-tion of biological mechanisms uniquely defining a human being. These biological mechanisms cannot unfold in a vacuum; they unfurl in the environments defined by ‘humanness’, that is, in the human habitat. The idea that both internal forces hidden in an individual, as well as the external characteristics of the habitat, guide the devel-opment of a human being has been central to social and behavioral sciences since their very emergence. Relevant challenges and debates have not really been about whether either matters, but rather about what constitutes internal and external forces of development and how their various elements interact with each other. One of the charges of developmental sciences is to define these inter-nal and external ‘black boxes’ and to understand, as much as possible, direct, indirect, and interactive mechanisms of their functioning. The objective of this article is to sample from the modern body of knowledge on the content and function of one of the many internal forces guiding development – the human genome.

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