Hundreds of prescription genetic tests are now available for every­thing from depression to cancer to Alzheimer’s disease. Such testing does hold promise, says David Flannery, M.D., medical director of the American College of Medical Genetics and Genomics. But he cautions that widespread genetic testing is still unwarranted.

Here’s advice on several genetic tests that make sense for at least some people, as well as some that aren’t yet ready for prime time: 

Heart Conditions

It’s now possible to check for two inherited heart conditions: familial hypercholesterolemia (very high cholesterol), and hypertrophic cardiomyopathy, a thickening of the heart muscle, says Donna Arnett, Ph.D., a cardiac epidemiologist at the University of Kentucky College of Public Health in Lexington.

When to consider testing: For familial hypercholesterolemia, testing can make sense if you have a family history of high cholesterol and an LDL of more than 190 mg/dl confirmed on two occasions. For that condition, and for hypertrophic cardiomyopathy, testing might also be worthwhile if a first-degree relative (parent, sibling, or child) has the disease.

How it can help: One study found that only 20 percent of people with familial hypercholesterolemia who were treated with cholesterol-lowering statins developed heart disease­ over 12.5 years of follow-up, compared with nearly 40 percent of those not treated.

And if testing reveals cardiomyopathy, it’s wise to have an electrocardiogram and echocardiogram every three to five years, depending on your age. If any heart muscle thickening is found, your doctor may monitor you more closely or prescribe heart medications such as beta blockers.

When to skip it: Nix testing if you have no family history of either disease or, in the case of familial hypercholesterolemia, your total cholesterol is less than 250 mg/dL or your LDL is less than 190 mg/dL. 

Breast Cancer

Mutations to two genes—BRCA1 and BRCA2—cause up to 10 percent of breast cancers and 15 percent of ovarian cancers. These mutations have also been linked to melanoma and pancreatic and prostate cancers.

When to consider testing: Testing might be useful if you have a personal or family history of breast or ovarian cancer, a relative known to have a BRCA variant, or if you have an Ashkenazi Jewish heritage plus a close relative with breast or ovarian cancer; some BRCA variants are more common in that group.

How it can help: Women with either gene mutation can have more frequent breast cancer screening. They could also consider the breast-cancer-prevention drug tamoxifen or even preventive mastectomy or the surgical removal of the ovaries.

When to skip it: Say no if you don’t have a strong family history of breast cancer. “Patients are still frequently sent to me who aren’t good candidates,” Flannery says, such as women whose family history “turns out to be just two cases on opposite sides of the family.”

Colon Cancer

About 3 to 5 percent of colon cancers stem from an inherited condition called Lynch syndrome (hereditary nonpolyposis colorectal cancer), which also increases the risk of ovarian, pancreatic, and stomach cancers.

When to consider testing: You might want a genetic test if you have a blood relative who was diagnosed with colon or uterine cancer before age 50, or more than two people on the same side of your family with colon, endometrial, ovarian, pancreatic, or stomach cancer, says Mary Freivogel, M.S., president-elect of the National Society of Genetic Counselors.

How it can help: People with Lynch syndrome have up to an 80 percent higher risk of developing colon cancer. So it’s a good idea for them to have an annual colonoscopy to remove potentially precancerous polyps, instead of doing so every three to five years as is usually recommended for people with polyps.

When to skip it: If you don’t have the hereditary red flags noted above, there’s little reason to have the testing.

Depression

Researchers have identified several gene variants that can undermine your body’s ability to metabolize the P450 enzyme—making antidepressants less effective.

When to consider testing: Genetic tests may help if you’ve been on several antidepressants for months or years and have not noticed an improvement.

How it can help: The test can suggest that you need a different dose or a different drug, says Robert Klitzman, M.D., professor of psychiatry at Columbia University.

When to skip it: Hold off on testing if you’re recently diagnosed or are responding well to medication. Although the test is covered by Medicare and some commercial insurance, there’s not enough evidence to recommend it for wider use, according to the independent Evaluation of Genomic Applications in Practice and Prevention Working Group. 

Celiac Disease

Researchers have linked celiac disease—a reaction to gluten, which can seriously damage the intestinal lining—to two genes, HLA DQ2 and DQ8. People with both of those genes have a 3 percent risk of having the disease, compared with 1 percent for those without the genes, according to the Celiac Disease Foundation.

When to consider testing: Talk to your doctor about testing if you have a parent, sibling, or child with celiac or if there’s a discrepancy between the blood test usually used as an initial test and a subsequent biopsy done to confirm that you have the disease.

A gene test can also make sense if you’ve eliminated gluten but need to confirm the diagnosis. That’s because a gluten-free diet can make the standard blood test and biopsy less accurate, says Peter Green, M.D., director of the Celiac Disease Center at Columbia’s College of Physicians and Surgeons in New York City.

How it can help: If you have the genes for celiac disease but don’t yet have symptoms, you don’t have to eliminate gluten from your diet. But it can make sense to periodically have blood tests to see whether the disease has emerged so that you can make dietary changes as soon as possible.

When to skip it: Don’t bother with the testing if you’re just curious whether you have celiac. Even if you test positive, you need to have a blood test and biopsy to confirm the diagnosis before resorting to a gluten-free diet. Being on a gluten-free diet when you don’t need to be boosts the risk of nutritional deficiencies.

Iron Overload

Up to one in every 200 people in the U.S. have this condition, also called hemochromatosis, which causes your body to store too much iron. That can lead to diabetes, heart problems, impotence, liver disease, and other problems.

When to consider testing: You may benefit from testing if have a family history of hereditary hemochromatosis or if routine blood tests reveal high iron levels.

How it can help: Treating iron overload early can often prevent complications.

When to skip it: If you don't have signs of iron overload or a parent, sibling, or child with the condition, you don’t need testing. 


Genetic tests for some conditions that affects the eyes, like the one shown here, don't always work.

Two Genetic Tests to Skip

The following tests are sometimes recommended by doctors, even though research shows they are inaccurate or have no effect on treatment options:

Macular Degeneration

Some doctors say that testing people with age-related macular degeneration (AMD) for certain gene variants can help determine whether the patients would benefit most from a supplement with only zinc and copper or one that also has vitamins C and E, lutein, and zeaxanthin.

Why skip it: The study behind that recommendation was funded by the very lab that performs the gene test. And it was refuted by a major 2015 National Eye Institute study. “Genetic tests for AMD have no proven benefit for treatment for the patient being tested,” says study lead author Emily Chew, M.D., deputy clinical director at the National Eye Institute. The standard supplement formula, called AREDS, works equally well for all groups, she says. 

Alzheimer's

One genetic test screens for an early onset form of the disease; another for a gene, APOE, that increases the risk of developing it later in life.

Why skip it: Early onset Alz­heimer’s accounts for less than 1 percent of dementia cases. And the test for the APOE gene isn’t very accurate: Though about 15 percent of Caucasians and 25 percent of African-Americans have the variant, that doesn’t mean they’ll develop the disease.

Last, “there’s no way to prevent Alz­heimer’s, so you can’t do anything differently to reduce risk, and in fact knowing the gene is present can cause anxiety, or discrimination in obtaining long-term-care insurance,” says Heather Snyder, Ph.D., senior director, Medical & Scientific Operations at the Alz­heimer’s Association. 

Editor's Note: This story has been modified to clarify that the cancer risks associated with the BRCA1 and BRCA2 genes stem from certain mutations to those genes, not the genes themselves.