A good reason to get a gene test: you believe it could help you make an important decision or target your efforts to protect your health.
But sometimes the test isn’t necessary. If diabetes is common in your family, for instance, it’s especially important to maintain a healthy weight, exercise, and ask about your blood sugar levels at checkups. You don’t need the evidence of a particular gene.
Medicine is moving towards giving more tools to patients — you now can get an OTC test for HIV, strep infection, allergies to 10 common allergens, urinary tract infection, cholesterol levels, thyroid function, blood pressure, and blood sugar levels. However, gene test results are complex and can frighten you unnecessarily. You could also frighten your loved ones, if family members assume that their risks are similar to yours. The results may be ambiguous. Even if they are clear, they may not be useful, or accurate. There are many millions of variants, and many are rare or not understood. Even when we know a variant is tied to a disease, we may not know how much it increases risk.
If you’re simply curious about what your genes could reveal, be prepared: most people get a possibly scary answer. In one study, researchers recruited 199 patients of a large health maintenance organization and offered them free testing. On average, they turned out to carry at least one variant associated with increased risk for six of eight health conditions.
Stick to genetic information you can use. The most reliable, and immediately helpful, information may be an analysis of your potential response to particular drugs, including the blood thinners clopidogrel (Plavix) and warfarin (Coumadin). The Food and Drug Administration has approved labeling on warfarin that suggests doctors use genetic tests to optimize dosing. Note that some evidence indicates the test-based dosing doesn’t work as well for African Americans.
Genetic testing can give you the push you need to take precautions. For example, in a small study, people who learned that they carry the APOE ε4 gene, which puts them at higher risk of Alzheimer’s disease, were almost six times more likely to have bought long-term care insurance or increased their coverage than people who tested negative. Exercise can help defend you against dementia, so if you think a positive result on the APOE ε4 gene would motivate you to start running, run to the doctor.
Let’s say you have several close blood relatives who have the same kind of cancer. Experts recommend genetic testing if you have a personal or family history that suggests a heritable cancer and the test results can give you useful information.
Just be clear: the presence of a gene variant linked to a cancer doesn’t mean it’s certain you’ll develop cancer.
One reason is that you have two copies of most genes, one from each parent. If the gene is dominant, you can develop cancer passed on through a gene from one parent. If it is recessive, you need to get the variant from both parents. If the variant is only carried on the X chromosome and recessive, sons will get it from their mothers, who give them their X chromosome. But daughters have two X chromosomes, one from each parent and will need the variant on both to be at risk.
Even if you have a dominant variant, two copies of a recessive variant, or are male with a variant on your X chromosome, you may not get cancer. Some genetic variants never create cancers in some people, or the severity may vary dramatically.
We know of more than 50 hereditary cancers, most of which are dominant. Some of the more common cancers for which you can be tested are included in this list from the National Cancer Institute:
Genes: BRCA1, BRCA2
Related cancer types: Female breast, ovarian, and other cancers, including prostate, pancreatic, and male breast cancer.
Related cancer types: Breast cancer, soft tissue sarcoma, osteosarcoma (bone cancer), leukemia, brain tumors, adrenocortical carcinoma (cancer of the adrenal glands), and other cancers.
Related cancer types: Breast, thyroid, endometrial (uterine lining), and other cancers.
Genes: MSH2, MLH1, MSH6, PMS2, EPCAM
Related cancer types: Colorectal (or colon), endometrial, ovarian, renal pelvis, pancreatic, small intestine, liver and biliary tract, stomach, brain, and breast cancers.
Related cancer types: Colorectal cancer, multiple non-malignant colon polyps, and both non-cancerous (benign) and cancerous tumors in the small intestine, brain, stomach, bone, skin, and other tissues.
Related cancer types: Eye cancer (cancer of the retina), pinealoma (cancer of the pineal gland), osteosarcoma, melanoma, and soft tissue sarcoma.
Related cancer types: Pancreatic endocrine tumors and (usually benign) parathyroid and pituitary gland tumors.
Related cancer types: Medullary thyroid cancer and pheochromocytoma (benign adrenal gland tumor).
Related cancer types: Kidney cancer and multiple noncancerous tumors, including pheochromocytoma.
Gene tests can help doctors diagnose these diseases, determine the severity of a disease, and guide you in deciding on the best medicine or treatment.
If you are pregnant or considering becoming pregnant, you might want to know if you have a gene variation linked to disease that you can pass on to your child, especially if your family has a history of birth defects or disabilities. Your test results may give you relief from unnecessary anxiety — or perhaps prompt you to adopt a child instead.
Newborns receive a heel “prick test” in hospitals, drawing blood. The results can lead to further testing. Check the National Newborn Screening and Global Resource Center for more information.
August 26, 2016
Christopher Nystuen, MD, MBA