Think Before You Spit: Do Personal Genomic Tests Improve Health?

Posted on by Muin J Khoury, Director, Office of Public Health Genomics, Centers for Disease Control and Prevention

Think Before You Spit- a woman looking at a test tube

Campaigns against public spitting in the 19th century were largely driven by concerns about the spread of tuberculosis. However, at the beginning of the 21st century, spitting seems to be making a comeback.  Over the past few years, several companies have begun offering personal genomic tests online to the public. There have been famous images of “spit parties”, where celebrities are seen filling tubes with saliva to ship for DNA testing. Getting information on one’s genes has been promoted as fun, as part of social networking, and as a basis for improving health and preventing disease.

When it comes to spitting to improve one’s health, we say: think before you spit.  Our knowledge of the potential benefits and harms of these tests is incomplete at best.  Despite exciting research advances in genomics of common diseases, there is still much to learn about what this information means and how to use it to prevent disease. A little bit of incomplete or inaccurate information may even be harmful.

There are at least 2 key questions to consider when deciding whether personal genomic tests are worth your spit. First, how well can these tests detect or predict particular health conditions?  Most common diseases, such as diabetes, cancers, and heart disease, are caused by multiple genes and interactions with environment and behavior. Therefore, a risk estimate based only on genes is bound to be uncertain and can rapidly change based on new information. Different companies may even arrive at different interpretations of the same information. In 2010, a special undercover investigation by the Government Accountability Office found that tests by different companies of the same samples gave contradictory results. Second, can the test provide additional information that leads to better health? If the test indicates increased or decreased risk for a disease, what can be done about it? Will the test tell us more than what we know to do already?

Many interventions for reducing one’s risk for common diseases–such as smoking cessation, weight loss, increased physical activity, and blood pressure control–are beneficial regardless of a person’s genetic background. In the words of one consumer who responded to the CDC podcast on personal genomics in 2010:  “…seems one should just assume you have many health risks, then take really good care of yourself to lessen risks. Pretend you did the tests. Get ‘pretend-scared’ straight! You can then motivate yourself to keep healthy weight, exercise, reduce stress, get enough rest, consume healthy foods, avoid unhealthy habits,  enjoy hobbies & keep mind active, build friendships & family bonds…” In fact, new data from CDC  show that people who engaged in four healthy behaviors — not smoking, eating a healthy diet, getting regular physical activity, and limiting alcohol consumption- had much lower likelihoods of dying (over an 18 year period) from cancer, cardiovascular disease and other causes than those who did not engage in all four healthy behaviors.  Not smoking provides the most protection from dying early from all causes.

Several scientific studies designed to evaluate the potential impact of personal genomic information on health behavior and outcomes have been published and more are under way. Recommendations for setting scientific standards and a research agenda for personal genomics were published in 2009 by a panel convened by the Centers for Disease Control and Prevention and the National Institutes of Health.  Those recommendations for scientific evaluation still hold today.

In 2008, Dr Kari Stefansson, a leading scientist in the genetics community and founder of one of the companies that offer personal genomic tests said: “I am convinced that within five years every college-educated person in America is going to have a [genomic] profile like this. You cannot afford not having this.”  While this prediction may or may not be fulfilled based on the evolving scientific evidence, when a valid and useful test becomes available, the public health imperative is to have such tests widely available,  regardless of educational levels or other socioeconomic factors. For example, a recent national survey found that BRCA1/2 testing for breast and ovarian cancer—which is clearly beneficial for some women at high risk—is underutilized, especially among black and Hispanic women.

A very informative and inexpensive “genomic test” is available right now: family health history. An accurate, updated family health history can help healthcare providers assess the presence of many genetic conditions and whether patients and their relatives may have an increased risk for specific diseases. Family history also captures shared genetic, environmental and cultural disease risk factors.

We are interested to receive your thoughts about the use of personal genomic tests to improve health and prevent disease.

Posted on by Muin J Khoury, Director, Office of Public Health Genomics, Centers for Disease Control and PreventionTags , ,

11 comments on “Think Before You Spit: Do Personal Genomic Tests Improve Health?”

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    Is this really the CDC’s position? I’m shocked. I would think they would want as many people as possible to have their raw SNP datasets so that in the event there was an epidemic – genetic information could possibly be used to prioritize care for the population and/or identify and mitigate adverse or positive responses to vaccines or treatments. Before you write a post …. think.


    “A very informative and inexpensive “genomic test” is available to everyone right now: family health history.”

    Well, that’s not entirely the case. I know a lot of adopted families and information is not always available to them. And I also know plenty of genetic families with limited access to information for various reasons (such as death or dysfunction). There are also cultural situations that preclude or confuse this conversation.

    I would think CDC would want as many people as possible to have their raw SNP datasets so that in the event there was an epidemic genetic information could possibly be used to prioritize care for the population and/or identify and mitigate adverse or positive responses to vaccines or treatments. Think of how helpful it would have been if we knew for certain a segment of the population was immune to a virus or conversely very susceptible.

    I will get a personal genomic test in a few years. I consider it as contributing to self knowledge (“Know thyself”). I realize that there is a difference between phenotypes and genotypes and I won’t go running to my FP for unnecessary testing.

    What I wish is that by paying for this knowledge, I could contribute to a larger DB which could contribute to further genomic knowledge about the human condition.

    The clinical utility of genetic tests alone for predicting common diseases is doubtful for the reasons you say (multiple genes and interactions with environment and behavior.)

    The statement (implication?) that they “may do harm” is though pure speculation, as is the article that you link to. In fact you say “absence of evidence is not evidence of absence”. Nor is it the evidence of presence, it’s just a meaningless soundbite. By exactly the same criteria family history “may do harm”. Also the denial of access to DTC genetics “may do harm”

    “A very informative and inexpensive “genomic test” is available to everyone right now: family health history”

    “Family history also captures shared genetic, environmental and cultural disease risk factors.”

    But is this correct?

    1. As you say multiple genes are involved in common diseases – anywhere from 20-50 according to the GWAS studies. Common SNPs in many genes makes for a very complex pattern of inheritance from parents, let alone grand-parents.

    2. As for non-genetic factor how much real sharing is there? I spent the first 20 years of my life in the same house as my parents. For most of those years my diet and lifestyle was very different – the immediate environment was mostly similar. But this overlooked a perhaps more important fact that my first 20 years were completely different in every aspect to the first 20 years of both my parents, and even more different to the early years of all my grandparents. Overall the proportion of relevant “shared genetic, environmental and cultural disease risk factors” is very small.

    3. Elsewhere in a 2010 CDC publication you state “the utility of family history in public health has been poorly explored.”

    4. A recent study in the May 2011 issue of Genetics in Medicine found that Family history by itself is not a strong predictor of exactly who will acquire colorectal cancer within 20 years

    5. A recent much trumpeted conference presentation attempted to portray FH as the gold standard and demonstrate that it performed much better than genetic testing. But it did so only for highly penetrant hereditary cancers (which were not included in the DTC scan!). There was NO reported FH advantage for the common cancers, the rest of the 97% of colon cancers that is – see

    In your article about harm you say that very rigorous testing is required to establish harm/benefit before they should be used, and this should even include multi-year (decade?) RCTs. The same surely should apply to family history.

    If efforts to improve the use of genetics, its integration with FH and identifying where genetics maybe useful right now were the focus of this blog I think it would be more helpful. As the author of the FH vs DTC study above said if genetic tests were “used in concert with family health history assessments, those tests could become more effective and accurate”

    I first took a personal genome test in 2009 for genealogy purposes. The test also had a health-risk component that I was rather indifferent about. I figured that because I already know my family health history, what more could this test tell me? Well it did tell me something that I am high-risk for which isn’t something I knew about from knowing my familial health history. I don’t care to divulge what it is here but will tell you that it did result in causing me to exercise more.

    Who does “‘pretend-scared’ straight” work on? Doesn’t appear to work on smokers even when they see a TV ad with a woman who has a gaping hole in her neck. And it wouldn’t have worked on me either. I needed to have this information about my own genome to affect beneficial change in my life.

    Additionally, I take exception to the implication that people who are of lesser education or socioeconomic levels than academics or scientists are not equipped to have access to or understand their own genomic information. How many people on the College Dropout Hall of Fame would the CDC say, “You can’t handle the truth!”

    CDC’s Dr. Khoury is once again campaigning against genetic testing; his citation to support his “it might cause harm” is to another article he wrote! He does not bother to reference the NIH-conducted and other studies that demonstrate that consumer are not harmed by getting their genetic information through direct-to-consumer testing companies. He simply has no credibility anymore.

    In addition, why should the federal government interfere with a person who wants to learn as much as s/he can about her/his own body?

    I had a please of attending Illumina’s iDEA Conference recently. As you probably know, Illumina is the leading provider of personal genomic equipment and their CEO gave an example where personal genomic helped his friend to check for prostate cancer and had a real health impact. However, I agree with Dr. Khoury and others that personal genomics (in its current form) can not be used to improve human health. It can, however, be used for agriculture and animal studies and I wish everyone enveloped with NGS best wishes.

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Page last reviewed: April 8, 2024
Page last updated: April 8, 2024