In recent years, there’s been a dramatic increase in genetic testing. Dreamstime/TNS

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When it comes to health and disease — and, of course, many other aspects of life — one thing is certain: genes matter.

A single gene mutation can cause conditions such as sickle cell anemia or cystic fibrosis. More often, multiple genes are involved in disease development, and they act in concert with nongenetic factors, such as diet or exercise, to affect disease risk.

Several companies offer you the opportunity to look at your genes. But how might that help you from a health standpoint? And how do such tests differ from the genetic testing a doctor may recommend?

Consider the example of familial hyper­cholesterolemia (FH), a condition in which multiple variants of several different genes lead to markedly high cholesterol. This greatly increases the risk of heart attack, stroke and other health problems.

FH affects about one in 300 adults, which means it isn’t rare. Among adults who have the most common genetic variants that cause it, heart attack or sudden cardiac death may occur in middle age. Children who have a double dose of a gene variant linked to this condition may die of cardiovascular disease before age 20.

Treatments to reduce the risk of complications, such as cholesterol-lowering drugs, are available if a child or adult is known to have a mutation linked to FH.

Genetic testing is on the rise

In recent years, there’s been a dramatic increase in genetic testing. It was nearly unheard of only a few decades ago. Now, you or someone you know has likely had genetic testing within the last year or two.

And while healthcare providers can now order far more genetic tests for their patients than in the past, you don’t need a doctor’s order to request this.

Testing companies like 23andMe, Ancestry.com and others are ready and willing to check your genes for variants associated with certain health conditions, as well as your family ancestry. In fact, spending on direct-to-consumer genetic testing is predicted to reach $2.5 billion within the next few years.

Sometimes, tests are lifesaving

Is testing useful? For some people, the answer is clearly yes.

When performed accurately, genetic tests can uncover a disease or a tendency to develop certain conditions, and it can lead to close relatives getting tested as well. Preventive measures or treatment can be lifesaving.

Here are four examples (though there are many more):

Hemochromatosis. This is a genetic condition in which too much iron is absorbed from the diet. The extra iron can harm important organs like the heart and liver. Once a person is diagnosed, phlebotomy (blood removal, similar to what happens during blood donation) and avoiding iron supplements can prevent serious complications such as diabetes and liver failure.

Prenatal testing. For people planning pregnancy or who are already pregnant, genetic testing is available to check for many conditions, such as cystic fibrosis and Down syndrome.

Cancer. A number of genes are known to increase the risk of certain cancers. Testing may be especially important for people with a family history of these cancers. Perhaps the most well-known are BRCA mutations, which increase the risk of breast, ovarian and several other types of cancer.

People who don’t know their family’s medical history. A person who is adopted and has no information about family medical problems may learn from a test they are at increased risk of a preventable disease, such as heart disease or colon cancer. In these cases, knowing you might develop a condition or are a carrier can help direct medical care, and may inform life decisions or encourage you or other family members to consider genetic counseling.

Tests can be misleading

In other cases, testing is problematic. Results of genetic testing may provide information you already know, may be unhelpful, or may even be misleading.

For example, testing could reveal that you have a genetic mutation that rarely causes any health problems. Learning that you have this mutation may not help you — though it might alarm you.

Or, learning you’re at increased risk for developing Alzheimer’s disease late in life may be more upsetting than useful, as there are currently no reliably effective preventive treatments.

Genetic testing may have more than one kind of cost. A genetic test ordered by your doctor for a specific medical reason may be covered by your health insurance, but it’s unlikely that an over-the-counter test will be.

And, as one company states on its website, “knowing about genetic risks could affect your ability to get some kinds of insurance.”

When tests are not reliable

A study on testing for a genetic cholesterol disorder had some surprising results. This 2021 study published in JAMA Cardiology demonstrates how direct-to-consumer testing may be misleading.

The researchers looked at genetic testing for familial hypercholesteremia. They compared the results from a comprehensive panel of genetic testing ordered by doctors (which included more than 2,000 gene variants) with results from the more limited genetic testing (24 variants) provided by 23andMe.

Among more than 4,500 people tested for a medical reason, such as evaluating an unexpectedly high cholesterol level, the more limited testing would have missed important genetic variants for:

—nearly 70% of study participants

—nearly 94% of Black and 85% of Hispanic individuals

—about a third of Ashkenazi Jewish individuals

This suggests that a large number of people would be falsely reassured by the results of their genetic tests for FH if they relied on the type of screening offered by a popular over-the-counter product. And results may be particularly unreliable among persons of color.

In many cases, it’s best to review your decision to have genetic testing with your doctor before having it done. You may choose to see a genetic counselor about the ramifications of testing before you jump in, and let your doctor do the testing, rather than ordering it yourself.

Or, you may decide the best plan is no testing at all.

Dr. Shmerling is a senior faculty editor for Harvard Health Publishing.

© 2022 Harvard University. Distributed by Tribune Content Agency, LLC.