Unformatted text preview: Although the checklist approach is imperfect, it represented an enormous advance in both clinical care and research. For example, before the advent of DSM-III, it appeared that schizophrenia was twice as prevalent in the U.S. as it was in Great Britain. This discrepancy turned out to be an artifact of divergent approaches to diagnosis. In fact, the prevalence of schizophrenia is about 1 percent of people worldwide. The standardization of diagnosis made it clear that mental disorders are common and quite often disabling. According to the World Health Organization's data on the global burden of disease, major depression is the leading cause of disability in the U.S. and other economically advanced nations. In aggregate, mental disorders rank second only to cardiovascular diseases in terms of their economic and social costs in those countries. Meanwhile advances in neuroscience showed that certain neurological diseases leave unmistakable signatures on the brain. Parkinson's disease,
SEPTEMBER 2003 OVERVIEW/Improving Diagnosis
Because psychiatrists lack objective tests for detecting brain disorders, they sometimes fail to observe mental illness or mistake the symptoms of one disorder for another's. Scientists have recently found gene variants that seem to confer susceptibility to disorders such as schizophrenia and autism. Doctors may someday be able to determine a patient's risk of developing these diseases by analyzing his or her DNA. In addition, advances in neuroimaging may allow physicians to look for subtle anomalies in the brain caused by mental disorders. As the technology improves, doctors could use neuroimaging to diagnose psychiatric illnesses and to track the success of therapy. 98 SCIENTIFIC AMERICAN COPYRIGHT 2003 SCIENTIFIC AMERICAN, INC. for instance, is characterized by the death of nerve cells in the midbrain that make the neurotransmitter dopamine, a chemical that transmits signals between neurons. The definitive signs of Alzheimer's disease are deposits of an abnormal protein called amyloid and tangles of protein in the cells of the cerebral cortex, the outermost layer of the brain. (Because one needs a microscope to observe these anomalies, a conclusive diagnosis can be made only after the patient's death.) But when it comes to psychiatric illnesses such as schizophrenia and depression, the abnormalities in the brain are much more subtle and difficult to discover. For this reason, many researchers have begun to look for indicators of brain disorders in the human genome. FIRST STEPS TOWARD A GENETIC TEST?
PEOPLE WHO POSSESS DNA SEQUENCE VARIATIONS in any of the four genes shown below appear to have a slightly increased risk of developing schizophrenia. These genes are involved in the transmission of signals among neurons in the brain, so it is possible that the genetic variations disrupt that process. But posse...
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