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People do genetic testing with all sorts of questions on their minds, but one of the most complicated is: what does tomorrow hold? Is the future of my health written in my genes?

Our DNA plays a significant role in determining who we are, including how our bodies work. To some extent, we’re all at higher risk for some health conditions than others depending on the genes we have.

The most straightforward way people’s DNA can affect their health is through genetic conditions like cystic fibrosis or sickle cell anemia. Whether or not someone has these each of these conditions is purely determined by whether or not they inherit a defective copy of a specific gene.

In most cases, however, the picture is more complex. This includes common health conditions like heart disease and cancer.

Whether or not someone has one of these conditions has to do with a number of factors involving both environment and genetics. For example, we know that high-cholesterol diets increase people’s risks for heart disease. Therefore, we say that a high-cholesterol diet is an environmental risk factor for heart disease.

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However, environmental risk factors aren’t the only thing that determines whether people get heart disease. Some people are born more vulnerable to the condition than others. These are people with more genetic risk factors for heart disease – their genes make it more likely that they’ll have heart disease at some point in their lives.

The same holds true for many other health conditions. For instance, smoking is a significant environmental risk factor for certain kinds of cancer. But some people are also more likely to develop these forms of cancer based on their genes.

Generally, someone’s genetic predisposition to a given disease involves many different genes working together. Each gene has a relatively small effect because so many other genes are also in play, but in combination all these genes increase or decrease risk for a certain disease.

In some cases, a single genetic change can significantly change how likely someone is to end up with a given health condition. Some examples are:

  • The APOE gene. People with two copies of a certain variant are 15 times more likely to develop Alzheimer’s disease.
  • The LRRK2 gene, where mutations can dramatically alter one’s odds of developing Parkinson’s disease. Google founder Sergey Brin famously discovered via 23andme that he carried a mutation in this gene.
  • The BRCA1 gene, which has a large effect on women’s odds of developing breast cancer. Angela Jolie wrote about her experience discovering she had a mutation in this gene and undergoing a preventative double mastectomy as a result.

Although these are the largest known genetic risk factors for Alzheimer’s, Parkinson’s and breast cancer respectively, there are many other genetic risk factors involved in these diseases and other conditions. Most genetic risk factors don’t have such dramatic consequences by themselves and instead contribute only slight increases or decreases in total risk.

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It’s worth keeping in mind that when we talk about genetic risk factors, we’re talking about probability, so nothing is a given. You can be genetically predisposed to a certain health condition but never actually develop the condition, just like you can be genetically protected from a condition but develop it anyway.

That said, DNA tests can give you an idea of your overall risk for a given disease, which can help with planning ahead or making lifestyle changes. Occasionally, genetic tests will uncover genes that seriously alter the likelihood you’ll have a specific health condition, for better or worse. Often, the risk factors revealed by home DNA kits will be more subtle and open to interpretation – your future health may be written in your genes, but scientists are still making progress on how to actually read that information.

In any case, if you’re interested in a particular condition, remember to research what genes relevant to that condition the genetic kit you’re looking at tests for. Not every kit looks at all the relevant genes, and there’s still some ambiguity over how to interpret the genes kits do look at, but one thing is for sure: as a result of direct-to-consumer genetic testing, it’s possible learn more about what your future health might hold than ever before.