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How useful are genetic tests?
In some cases, the results of a genetic test confirm a physician's suspicion that the cause of a patient's symptoms is an alteration in the normal DNA sequence for a particular gene. Increasingly, this information can indicate to the physician what type of treatment may be best. Many diseases, however, are not caused by changes in a person's DNA sequence. Moreover, genetic tests cannot detect all changes in DNA that do cause disease. Some of the rarer genetic changes that cause cystic fibrosis, for example, are not detected by current tests.
Detected alterations in a DNA sequence in some cases may produce disease but do not always do so. For example, there are people with the gene alteration often responsible for fragile-X syndrome who exhibit few or none of the symptoms typical of that disease. Genetic tests, although they can often help physicians, are merely one more type of medical information. A test on the protein encoded by a gene, rather than on the gene itself, may yield the same information.
Genetic tests that can predict a likelihood of illness generally do not do so with certainty. Rather, they indicate an elevated risk of disease, much as a high cholesterol count indicates an elevated risk of heart problems. As science advances, it is likely that more tests will be developed that indicate some statistical propensity toward disease in later life.
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