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Unformatted text preview: ssing the variations is neither necessary nor sufficient to cause schizophrenia, which most likely arises by several pathways. In the future, as researchers learn more about the genetic and nongenetic causes of brain disorders, doctors may be able to estimate a patient's risk of acquiring a psychiatric illness by analyzing his or her DNA with a gene chip (at right).
25 24 23 22 Dysbindin
23 22 21 12 11.2 11.2 12 13 21.1 21.2 21.3 22 23 24.1 24.2 24.3 22 23 24.1 24.2 24.3 The Genetics of Disorder
behavioral traits are often passed from parent to child, certain mental disorders run in families. To determine whether the resemblance is a result of genes or family environment, researchers have conducted studies comparing the risk of illness in identical twins (who share 100 percent of their DNA) to the risk in fraternal twins (who on average share 50 percent of their DNA). Another type of study, which is more cumbersome, focuses on whether an illness in offspring who were adopted early in life is more often shared with their biological relatives or their adoptive families. Such studies reveal that genes play a substantial role in the transmission of mental disorders but that other factors must also be at work. For example, if one identical twin has schizophrenia, the risk to the other is 45 percent. If one identical twin has autism-- a developmental brain disorder characterized by impairments in communication and social interaction-- the other twin has a 60 percent chance of sharing the same diagnosis. These are enormous increases over the risks for the general population (1 percent for schizophrenia, 0.2 percent for autism), but the key point here is that some twins do not develop the disorders even if they carry the same genes as their affected siblings. Therefore, nongenetic factors must also contribute to the risk of illness. These factors may include environmental influences (such as infections or injuries to the brain early in life) and the random twists and turns of brain development. Even among identical twins growing up in exactly the same environment, it is not possible to wire up a brain with 100 trillion synapses in identical fashion. For all mental disorders-- and, indeed, for all normal patterns of behavior that have been studied-- genes are important, but they are not equivalent to fate. Our brains, not our genes, directly regulate our behavJUST AS NORMAL 21.3 21.2 21.1 12 11.2 12 13 14 15 16 21 22 23 24 25 26 27 Neuregulin 1 13 12 11.2 12 13 14 15 21 22 13 11.2 12 13 14 21 DAAO 31 32 33 34 G72 Chromosome 6 Chromosome 8 Chromosome 12 Chromosome 13 GENE CHIP IMAGE COURTESY OF AFFYMETRIX; SOURCE FOR CHART: NATIONAL ACADEMY OF SCIENCES ior, and our brains are the products of genes, environment and chance operating over a lifetime. What is more, new resea...
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This note was uploaded on 05/02/2010 for the course PSY 320 taught by Professor Na during the Spring '10 term at Suffolk.
- Spring '10