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What is genetic testing?
A variety of tests now makes it possible to examine a person's DNA to determine the sequence of the nucleotide bases at critical points within genes that, when mutated, can cause disease (see "How will the discovery of new genes help society?"). The DNA is typically obtained from a blood sample.
Certain DNA sequences have been shown to cause disease or increase the risk that a healthy person will develop a disease later in life. Genetic tests provide physicians with information about the DNA sequence of a particular gene for a particular person. With this information, a physician can prescribe drugs, special monitoring, or preventive measures to treat the disease or reduce the risk that it will develop. This is the subject of a new area of medicine called pharmacogenomics. Some people with an inherited predisposition to a type of colon cancer owe their lives to genetic testing. The test results prompted physicians to remove part of the colon before it turned cancerous.
Some genetic tests can detect whether someone may be a carrier of a genetic disease, even though neither parent is affected. If two carriers of the same disease have a baby, the baby may inherit the condition.
Some forms of genetic testing have already achieved wide acceptance: for example, many people of Jewish ancestry as well as French Canadians choose genetic testing to learn whether they are carriers of Tay-Sachs disease, a lethal condition, because the disease, though rare, occurs more frequently in these groups than it does the general population. Some people prefer not to have genetic tests that may indicate a tendency to develop illness, however, especially if there are no therapies to prevent or delay the condition.
As medical science advances, more genetic tests are likely to become available, and these will likely indicate tendencies to develop diseases not normally thought of as "genetic": diabetes, for example. Tests based on single-nucleotide polymorphisms (SNPs)-tiny but common genetic variations in DNA sequences-could fall into this category.
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