Can Your DNA Predict Which Diseases You’ll Develop

In a simple test, you send a saliva sample to a laboratory and receive a report some time later indicating that your risk of developing conditions such as Alzheimer’s disease, diabetes or certain cancers may be higher than average. Can such a test really reveal diseases that have not yet shown any signs?

The answer is, to some extent, yes. Scientists can now identify certain genetic variants associated with diseases and use this information to estimate an individual’s risk of developing them. This can help physicians recognize some risks earlier and plan preventive measures or further investigations.

However, one important point must be kept in mind: carrying a gene variant associated with a disease does not mean that a person will inevitably develop that condition. Genes can alter the likelihood of developing a disease, but they do not determine a person’s health future on their own.

Some Diseases Are Caused by Changes in a Single Gene

For certain diseases, the relationship between a gene and the condition is relatively well established. For example, according to the US National Cancer Institute (NCI), Huntington’s disease is an inherited neurological disorder caused by a specific alteration in the HTT gene. People who carry the relevant genetic change are expected to develop the disease, although the age at which symptoms begin can vary.

Another example involves certain hereditary cancers. The BRCA1 and BRCA2 genes play a role in repairing DNA damage. A disease-causing variant in either gene can increase the risk of breast and ovarian cancer. For this reason, testing these genes in families with a clear history of such cancers can provide physicians with important information.

Even in these cases, however, a test result does not mean that a person has cancer. Someone may carry a disease-causing BRCA variant and never develop the disease. Rather, the test indicates that their risk is higher than the population average and that closer monitoring or follow-up may be warranted.

When Multiple Genes Contribute to Disease Risk

The picture is more complicated for common conditions such as type 2 diabetes, high blood pressure and cardiovascular disease. In these cases, a single gene usually cannot be identified as the cause. Thousands of small variations in DNA may collectively influence the likelihood of developing a condition.

Consider type 2 diabetes. Some people have a greater genetic predisposition to the disease because of a combination of genetic variants. However, this predisposition does not determine the outcome on its own. Body weight, physical activity, diet, age and other factors also contribute to the development of the disease.

To assess the combined effects of genetic variants, researchers use a method known as a polygenic risk score (PRS). Rather than focusing on a single gene, this approach examines thousands of genetic variants. Each variant may have only a very small effect on its own, but their combined effects can provide an indication of a person’s genetic predisposition to a particular disease.

For example, an assessment might indicate that an individual has a higher-than-average genetic risk of cardiovascular disease. This does not mean that the person will inevitably experience a heart attack in the future. Instead, it suggests that other risk factors, including blood cholesterol, blood pressure, smoking and family history, may warrant closer assessment.

Can DNA Reveal the Risk of Developing Alzheimer’s Disease?

Alzheimer’s disease is an example of how genetic information can be useful in assessing disease risk while also illustrating its limitations.

According to information published by the US National Institute on Aging (NIA), one gene associated with the risk of the common, late-onset form of Alzheimer’s disease is APOE. This gene has several variants, one of which is known as APOE ε4. Carrying one copy of this variant increases the risk of developing Alzheimer’s disease, while carrying two copies can increase the risk further.

Having this variant does not mean that a person will inevitably develop Alzheimer’s disease. Conversely, many people who develop the disease do not carry this variant. Testing for APOE can therefore provide information about genetic risk, but it cannot, on its own, determine who will develop the disease in the future.

This distinction matters. If someone believes that a genetic test reveals their inevitable fate, they may become unnecessarily anxious. Conversely, a negative result may lead them to assume that they face no risk at all.

Genes Interact With Lifestyle

Why can two people with similar genetic profiles have different health outcomes over the course of their lives? The answer lies partly in the influence of environmental factors and lifestyle.

Diet, physical activity, sleep, tobacco use, air pollution and living conditions can all affect health alongside a person’s genetic predisposition. For example, someone who is genetically predisposed to heart disease may be able to reduce their overall risk by controlling blood pressure and cholesterol, exercising regularly and avoiding smoking.

This does not mean, however, that lifestyle changes can always eliminate the effects of disease-causing genetic variants. In some inherited conditions, the genetic predisposition is so strong that the risk remains substantial even when a person follows recommended health practices. Nevertheless, understanding that risk can help individuals and their physicians make more informed decisions.

For this reason, specialists do not rely solely on DNA test results when assessing the likelihood of developing a disease. Family history, age, physical health and environmental factors must also be considered alongside genetic information.

How Reliable Are At-Home Genetic Tests?

Today, some companies allow people to obtain genetic information without visiting a healthcare facility. Customers send in a saliva sample or a sample of cells collected from inside the mouth, and the results may include information about ancestry, inherited traits or the risk of developing certain diseases.

However, not all these tests are designed for medical diagnosis or clinical risk assessment. A company may examine only a limited number of genetic variants associated with a particular disease. In such cases, failing to identify those variants does not mean that a person has no other genetic predisposition to the condition.

Similarly, if a test indicates that someone has an increased risk of developing a disease, the finding may need to be assessed through clinical evaluation and, where appropriate, more comprehensive testing. For example, someone who receives an at-home test result suggesting an inherited cancer risk should not make decisions about treatment or preventive interventions solely on the basis of that report.

Consulting a physician or genetic specialist is important because the interpretation of a result depends on the type of test, the genetic variant identified and the individual’s family history.

Why Are Genetic Test Results Not Equally Accurate for Everyone?

One important limitation of genetic risk prediction is that its accuracy can vary across populations.

A substantial proportion of research investigating associations between genes and diseases has involved genetic data from people of European ancestry. As a result, some prediction tools developed using these data may be less accurate when applied to people with different genetic ancestries.

This issue is particularly important for polygenic risk scores because the effects of genetic variants may not be the same across populations. A result that is highly predictive for one population group is not necessarily equally accurate for everyone around the world.

Researchers are working to address this limitation by studying people from a wider range of genetic ancestries. The more data available from diverse populations, the greater the potential to develop more accurate and reliable prediction tools.

How Can Knowing Your Disease Risk Help?

The main value of genetic risk prediction becomes apparent when the results can inform better health decisions. For example, if reliable testing indicates that someone is at high risk of an inherited disease, a physician may recommend earlier screening or more regular monitoring.

In families affected by certain hereditary cancers, identifying disease-causing genetic variants can help guide appropriate surveillance and inform discussions about options for reducing risk. In some inherited cardiovascular conditions, identifying a genetic predisposition early can also lead to timely evaluation and treatment.

However, learning about one’s disease risk is not always an easy experience. Knowing that the likelihood of developing a condition is higher may cause anxiety, particularly when there is no clear way to prevent it entirely.

Genetic information may also have implications beyond the individual, as it can provide clues about the possibility that family members carry the same variant. For this reason, protecting the confidentiality of genetic information and obtaining appropriate counseling before undergoing certain tests are important considerations.

DNA Alone Does Not Determine Your Future

Scientists can now use DNA analysis to identify certain inherited diseases and estimate the risk of more complex conditions, including diabetes, Alzheimer’s disease and cardiovascular disease. This capability could help shift medicine away from waiting for symptoms to appear and toward identifying people at risk earlier.

However, genetic testing still cannot tell us exactly when we will become ill or whether we will develop a particular disease at all. Test results must be interpreted alongside family history, overall health and living conditions.

Ultimately, DNA provides valuable information about our genetic predispositions. This information can help us make better decisions about our health, but it is not a substitute for medical examinations, routine testing or informed clinical decision-making.