Genetic Screening: Another Way to Worry Healthy People?

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Last week the Food and Drug Administration approved the marketing of a 23-and-me, a test previously marketed as a way to trace ancestry, for screening individual’s genetic predisposition to certain medical diseases or conditions.

At first glance it might make sense. Screening to know one’s genetic profile for a disease should be helpful, right?

Not so.

As counterintuitive as it may seem, there are many reasons why this test is likely to cause more harm than help. Patients may come to us, asking about the test or, worse, with results in hand. What do we tell them?

Genetics Testing Comes to the Masses

Image of DNA strandThe genetics test 23-and-me has been available for a while, offering a simple way to, in broad strokes, trace one’s ancestry. In April of this year the FDA allowed the company to sell the product for detection of “genetic predisposition” of 10 diseases, ranging from the relatively common — Alzheimer’s — to the rare Gaucher disease.   Purchased on the internet, purchasers receive a collection kit in the mail. Spit in a tube, pay $199, and 6-8 weeks later receive a report outlining some of your genetic profile.

Making Genetics Simpler than It Is

The idea behind the test is that a chromosomal aberration or marker invariably leads to disease. At least this will be the idea in the minds of many people.

However,genetics is not that simple. The more researchers learn about our genetic code, the more complicated their work becomes. Genes turn one another on – or off. Environmental factors play a role. We may understand, one day, this complex interplay. More important, one day we might even know how to affect it. But not now.

Rare Diseases Are, Well, Rare

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There’s a geek joke about gravity: “it’s not just a good idea. It’s the law.”

The same applies to probability – just because we want certainty doesn’t mean we can achieve certainty. Bayes’ theorem tells us the rarer the disease, the less likely a positive test for it is correct. Screening, by its very nature, aims to identify rare conditions or diseases. This rule doesn’t go away simply because we are looking at DNA; given the vagaries of genetics it might even be more so. Many people undergoing screening will be told they are “at risk” for a problem they are unlikely to face.

Yes, You are at Risk. No, I Can’t Help You

A caveat of screening for disease is that there is no point looking for an illness we can’t do anything about. We screen newborns for thyroid disease and phenylketonuria because we can address them early and prevent long-term problems. We don’t screen for muscular dystrophy because we have nothing to offer if we find it. The diseases this genetics test finds are not ones that benefit from early intervention. Yes, you are at risk for Alzheimer’s. Sure, you can do crosswords, eat better, not use aluminum cookery, or whatever else someone has related to dementia, but in the end we have no idea whether these are of benefit. I do the crossword, but it’s because I like to.

Can I Sew That Label on For You?

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The label we can put on someone – we call it a diagnosis – can alter them for good or bad. We can all think of the patient newly diagnosed with diabetes who has gone from flabby and sedentary to fit and running marathons. But there is also the downside of labeling. An elegant study performed over 30 years ago monitored patients newly diagnosed with hypertension. Over the year following diagnosis they had more sick days from work than they had the year before. These sick days were in addition to the days spent at office appointments. This asymptomatic risk factor for disease made them think of themselves as “sick.” I fear genetics testing will create additional people who see themselves

Best Not to Know?

The goal of medical care is not to prevent death (if it is, we are quite unsuccessful), but to delay it when we can. We are all mortal; we just don’t, day to day, like to be reminded. Genetics screening has the potential to turn mostly well people into worriers. Otherwise, we are here to help people along their life journey.

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