Genetic testing, will it predict your future health?
The topic of home genetic testing comes up quite frequently with our patients. Should you get them done? What does the data mean? Should you change your behaviours based on your genes? Can DNA predict our health future?
What is a home genetic test?
These are test kits that typically involve collecting a saliva sample at home, then shipping it back to the company for analysis. Two popular direct to consumer DNA kits are those provided by 23andme and Ancestry.com.
What will my results show?
This can vary across companies. Typically, you will learn about how your genes differ from the ‘normal’. In turn, companies attempt to identify whether your risk for a certain condition is increased or decreased. They will report about health risks (risk of a certain dis- ease), trait reports (likelihood of having a certain feature such as eye colour), wellness reports (what your DNA tells us about lifestyle factors like diet, exercise, and sleep) and carrier status reports (whether you carry a certain gene associated with a disease). Some tests will offer insight about your ancestry and tell you what proportion of your DNA comes from specific parts of the world. Some genetic testing panels will also try to determine which foods we should eat based on our DNA (nutrigenomics). Others will tell us which drugs we might want to avoid, to minimize adverse reactions (pharmacogenomics). These tests hope to offer tremendous insight into our health. And as we move towards an era of precision medicine, learning about our genes certainly has a role to play. But are these tests currently as helpful as advertised?
A quick primer on genetics
Keeping in mind that these tests are picking up subtle differences in DNA coding of specific genes, let’s review the basics. Genes are made up of DNA. We get our DNA at birth and it remains largely un- changed throughout our lifetimes. This is our genotype. Some genes act as instructions to make proteins that have a biologic function and contribute to who we are and to our physical characteristics. This is our phenotype. We have about 20,000 to 30,000 genes. Each gene consists of between a few hundred DNA bases (those A, T, C, Gs) to more than 2 million bases. Every person has two copies of each gene, one from each parent. Most genes are the same in all people but a small number, less than 1%, are slightly different. These differences, also called a genetic polymorphism, are what we are trying to find. The available consumer tests will often identify what is called a single nucleotide polymorphism (SNP), which refers to a single DNA base for a specific gene being different.
The promise of genetic testing
Once the world was enthralled by the prospect of de- coding the human genome to figure out what genes did. The idea was that once the human genome was mapped out, we would have all the answers about physiology and we’d be able to predict who would get what diseases. Unfortunately, this didn’t pan out. It turns out that biological determinism didn’t work. Meaning, our specific set of genes given to us at birth, do not provide nearly enough information to tell us about who we are and what our health destiny is. Now with the help of large data sets of DNA, re- searchers are seeking patterns to see if specific SNPs or clusters of SNPs can, together, predict health risks. So far, human biology has proven too complex.
Is genetic testing helpful?
Think of your DNA as though it is a blueprint for a house. Now say that house has a leaky roof. That blueprint may or may not have had a design flaw leading to that leak. But It turns out that the most important factor determining whether that roof leaked was the environment. Did it rain a lot? Was the roof maintained? This is a very big deal and in the genetic world, is called epigenetics. That is, the influence of environment and behaviours on how our genes work. In general, it’s felt that what our genes are doing is more important than what genes we have. Having a gene doesn’t tell us whether this gene will be turned on or not, or how active it will be. That’s because the environment will control expression of genes. So genes are not our fate. But rather, how they interact with our lifestyle and environment is what predicts health. And this is terribly complex. And can’t be measured by a DNA sample alone. There have been numerous examples of gene tests that simply don’t predict health outcomes as we’d expect. Across populations, we can see trends but this can be difficult to apply to an individual, and is scientifically fraught with error. In one study, whether someone was told they have the ‘good’ gene or not, was more powerful for outcomes than whether they actually had the gene in question.
What are the potential harms?
These tests can vary in reliability and the validity of their interpretations is not universally accepted. What can be labelled a ‘problem’ or ‘risk’ or ‘disease’ may in fact not be accurate or may not apply. As data emerges, these risk scores can change. We have seen patients inaccurately portray their results as a disease when it is not. Thinking incorrectly that one has a ‘bad’ gene can actually lead to bad health outcomes. In one study, people who were told they have a bad exercise gene actually performed worse in repeat testing, when in fact they didn’t have that gene. The power of the mind is often stronger than a lot of these genes. Contrary to most SNPs tested, some gene variations have a strong penetrance, meaning if you have it, you do have a strong risk of serious disease. People need to be ready to hear this information and likely should have access to a health professional to go over the data and not be facing a screen alone with bad news.
In Canada, law prohibits any person from requiring an individual to undergo a genetic test or to disclose the existing results of a genetic test. It is also prohibited to collect someone else’s genetic material without their consent. At present, this appears to protect us from discrimination, or discriminatory rulings, against our genetic material. Keep in mind, however, if you discuss your genetic results with your physician and that note gets entered into their record, their record can often be requested by third parties. Many of the direct to consumer DNA testing kits offer lengthy explanations about how they take privacy seriously, which of course is excellent. However, in the era of common data breaches, there may be cause for concern. For businesses, there is also a lot of value in collecting large amounts of genetic data, and this data is often sold to other companies for research purposes. Just be aware of this when sending in your DNA samples. You could have your genetic information shared with unknown others.
Should I get this test done?
We are in the era of precision medicine. Data holds potential and knowledge is powerful. So while a lot of these DNA tests aren’t likely as predictive as we had hoped, they can offer clues and be motivating in the right setting. As doctors, we do see significant value in these gene tests as it relates to potential adverse drug events. As mentioned, certain genes penetrate stronger into our physiology and can be deterministic; certain breast cancer genes, certain colon cancer genes, some Alzheimer’s genes, and some longevity genes, for example. In reality, most disease is polygenic—involving multiple genes—and hugely impacted by environment (ie. how we live our lives, what we eat, how we sleep, how handle stress, and how often and with what intensity we move). The totality of these influences is difficult to measure and quantify. The other reality is most strong genetic traits are better learned from understanding your family history. We often don’t dig deep enough here. We might argue about whether a certain gene or cluster of genes will result in early disease. But if you have a family history of very early breast cancer or heart attacks or even many thriving 90-year-olds in your family, then this is important. The bottom line is: it’s rare that information from these genetic tests will alter our practices and recommendations. They simply do not tell you your fate. But, they do offer some insights, and if you can accept most interpretations with a grain of salt, then they can be entertaining and perhaps you will learn a few things about your ancestry. —LP
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