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Excerpted from chapter 1 of Genetics and Mental Retardation Syndromes: A New Look at Behavior and Interventions, by Elisabeth M. Dykens, Ph.D., Robert M. Hodapp, Ph.D., & Brenda M. Finucane, M.S.
Copyright © 2000 by Paul H. Brookes Publishing Co. All rights reserved.
Toward Etiology-Based Work
Over the past few decades, advances in human genetics have brought revolutionary changes to the mental retardation field. With new genetic causes of mental retardation discovered each year, more than 750 genetic mental retardation etiologies have now been identified (Opitz, 1996). And, given the success of the Human Genome Project, these rapid advances show no signs of slowing. Indeed, in the late 1990s geneticists estimated that the chemical structure of each of the 100,000 human genes would be known by the year 2003 (Goodman, 1998), leading to a better understanding of the connections between particular genes and specific human behaviors (i.e., "gene–behavior correlations"). These advances mark a new era in our understanding of and interventions for people who have mental retardation.
Looking back, it is startling to see how far we have come in so short a time. Until Watson and Crick's discoveries were reported in 1953, the world did not even know the basic structure of the human chromosome, how many chromosomes human beings possessed, or how genes operated. In 1959, Lejeune, Gautier, and Turpin discovered that most cases of Down syndrome are caused by an extra — or third — chromosome 21 (i.e., trisomy 21). A decade later Lubs (1969) first observed the pinched, "fragile" site of fragile X syndrome, and, over the past two decades, discoveries in fragile X syndrome, as well as in Prader-Willi syndrome and Angelman syndrome, led to new models of human disease. In short, these advances are promoting a new way of looking at a variety of human disorders and permanently changing the disability field as a result.
This book describes these remarkable genetic advances as they apply to behavioral issues within specific mental retardation syndromes. To promote understanding of the behavioral characteristics of several genetic mental retardation disorders, we provide in each chapter descriptions of causes, prevalence, and basic physical characteristics for each syndrome, along with more in-depth understandings of many different behavioral characteristics.
GENETICS AND BEHAVIOR: A CRITICAL LINK
This book goes beyond mere description to advance a larger argument. Simply put, we argue that genetic disorders affect various aspects of behavior, from cognition and language to adaptive and maladaptive behaviors. More indirectly, the behaviors often exhibited by people with a particular genetic disorder also influence how others react. In the first few decades of the new millennium genetic disorders will also increasingly influence the choice of which specific psychological, educational, or other therapies are most effective for individuals with a given syndrome. To us, then, genetic disorders matter in understanding the behaviors of people with mental retardation.
The assertion that "genetic disorders matter" is obvious to some researchers, anathema to others. Indeed, to professionals in many disciplines, our argument will seem so obvious that it is hardly worth stating. To these people, the importance of genetic etiology shows itself every day. In other disciplines, however, workers cringe at the idea of etiology-based research or intervention. To these individuals, our arguments concerning the importance of genetic etiology on behavior seem obviously wrong, at odds with major philosophies in the field, and heretical to good science or practice. How, then, can we best reconcile such diametrically opposed views on the same topic? We first offer answers to several common criticisms of etiology-based approaches