Is genetic testing for disease a good idea?

November 30, 2008

(ChattahBox) — Genetic testing has been offered since the 1970s, but scientific knowledge about links between genes and certain diseases has increased significantly in recent years. It’s now possible to perform tests on more than 1,500 genes, but this is only a fraction of the 20,000 to 25,000 genes contained in the human genome, the number of tested genes has doubled in the past decade. The number of available tests has grown quickly as well. There are now 4,000 to 5,000 tests for heritable conditions (many of which are rare diseases), and separate tests for certain types of cancer and leukemia. 

The growth of online, direct-to-consumer companies has led to a transformation of the industry, according to Global Industry Analysts, Inc., a market-research company that released a comprehensive report on the subject in October. By analyzing sales figures for genetic tests in North America, the company determined that the market grew from $488 million in 2003 to $1.1 billion in 2008.  The size of the market means that consumers can obtain genetic and genomic tests from numerous sources, but aside from a requirement that tests be done in a federally certified lab, no regulatory body evaluates the claims of one test over another.  For example, a patient worried about breast cancer could purchase a test from the online company DNAdirect for a base price of $620. The customer is then sent a kit, which he or she returns with a blood or cheek-swab sample. Though the company offers pre-test education and access to genetic counselors, the experience is very different from testing in a clinical setting, where patients are closely monitored by a doctor and a geneticist who specializes in the disease.

Before undergoing genetic tests of any kind, however, it’s crucial that patients fully understand their promise–and their limitations. Only certain tests can conclusively tell a patient if he or she possesses a gene directly related to a disease. In the cancer field, these include genetic testing for stomach, colon, ovary and breast cancers. Many genetic and most genomic tests tell patients their probability of developing a disease at some point in the future, and not all tests are comparable. Unfortunately, there’s a strong chance that some consumers aren’t learning anything useful about their health when they pursue testing.

“Most of the ‘genomic’ health-risk tests being sold directly to consumers have not been proven to be valid in the same way we study new drugs, for example,” says Dr. Kenneth Offit, director of the Clinical Genetics Service at the Memorial Sloan-Kettering Cancer Center in New York.

For this reason, he believes that patients should pursue genetic testing under the supervision of a trained geneticist–and only if the patient plans to act on the result or if a test might resolve unanswered questions about family history and personal health.


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