popular genetic testing services may sometimes be mistaken about the cancer risk of a client, according to a new study. When the test results for a small group of patients were compared to their risk calculated from the history of the family, the results differ about half the time.
Several companies have emerged in recent years that scan the entire genome of customers for the SNP called DNA glitches that may influence the risk of developing common diseases of a person. Most SNPs relating only slightly increase the risk of disease, however, and the usefulness of these so-called personal genome scans is widely debated.
To explore this issue, medical geneticists cancer Brandie Heald Leach and Charis Eng of the Cleveland Clinic in Ohio has recruited 22 men and women of the genetics of cancer clinical Eng. (Patients either had cancer themselves or had a family history of the disease). Spouses of patients also participated for a total of 44 subjects. Leach and Eng sent samples of the saliva of patients with Navigenics, one of the SNP test companies, which returned results which included the risk of cancer. The researchers also interviewed each subject about his family history of cancer and have calculated a risk of breast cancer (for women), prostate cancer (for men), and colon cancer.
The history of the family and the results Navigenics put roughly the same proportion of the population (40%) in a class at moderate or high risk for the three cancers. But the results were only about half the time in agreement. For example, eight men with normal risk for prostate cancer based on family history were high risk according Navigenics. And now came with a normal or moderate risk for new patients who clearly had a high risk of colon cancer based on the story, including the family of five who even carried mutations for an inherited form of cancer colon.
This Navigenics found a lower risk of cancer than the analysis of family history is not surprising, Eng said, because the company does not test the handful of genes well known hereditary cancer, such as breast cancer. (Another company, 23andMe, testing for breast cancer genes BRCA1 and BRCA2 but not others, said Eng.) Although geneticists are well aware that the tests like Miss Navigenics these high-risk genes, "it is not easy for primary care physicians or patients," says Eng. She fears that some people who take tests "could be falsely reassured or falsely alarmed." Leach presented results in Washington this week at the annual meeting of the American Society of human Genetics.
Greg Feero of the National Institute for research on the human genome in Bethesda, Maryland, agrees that history of the family is still the gold standard for assessing the risk of cancer from one person: "it remains to be seen whether the current SNP tests actually add any value," he said
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