Can a genetic test tell you if a medication will work?

The Pediatric Insider

© 2019 Roy Benaroch, MD

“Personalized” medicine sounds appealing. Rather than just guessing at what medication to try, a genetic test can figure out, in advance, which medications will be effective and which medications are more likely to make you sicker.

Except it doesn’t work. It’s mostly marketing and hype.

The FDA has officially warned consumers and physicians that genetic tests sold to predict patient responses to medications shouldn’t be used. They’re not FDA approved, and in most cases there’s no reason to think that these tests can accurately predict how a medication is metabolized or what it’s likely to do when you take it. These tests are being aggressively marketed to the general public and to physicians, and they don’t deliver what they promise.

Medicines for conditions like depression, acid reflux, and heart disease have been highlighted by the FDA – though many other medicines have become targets for these tests, too. And these tests do reveal certain genetic “polymorphisms” (variations) that all of us carry, variations that affect the way medicines are metabolized and processed in our bodies.

The problem is that our knowledge about these polymorphisms is rapidly evolving, and it’s far from complete. It turns out that dozens or maybe hundreds of genes can have overlapping functions, and (with few exceptions) we don’t yet know all of the genes involved. And for each gene, there may be hundreds or thousands of variations in the general public. Or, maybe, some of us have a unique variant that hasn’t been seen before. These companies have no way to test the gene variants to know their function. They rely on proprietary databases, riddled with incomplete data and assumptions.

Just one example: when the MTHFR gene and its variants was first described, it seemed like MTHFR polymorphisms could have wide-ranging and significant health effects. It turned out that’s completely wrong. MTHFR “variations” are so common in the general public that it’s fair to say we all have polymorphisms, and almost none of these has any clinical importance. Even the 23andMe company, which makes money selling genetic tests, discourages MTHFR testing, saying “Despite lots of research – and lots of buzz – the existing scientific data doesn’t support the vast majority of claims that common MTHFR variants impact human health.” Still, many families are still relying on misguided MTHFR testing pushed by naturopaths and chiropractors to make health decisions. And this is just one of the hundreds of genes these kinds of tests rely on.

Genetics shows great promise, and I think the future includes a big role for genetic testing. But we don’t have the knowledge, yet, to use the results of these tests to better-guide therapy. But that doesn’t mean that therapeutic decisions, now, are entirely guesswork. Reviewing a family history and the exact nature of a problem often gives physicians some good clues to help guide decisions. I know, that sounds old-fashioned. But talking and listening remain the best ways for docs and patients to work together to make the best decisions.


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2 Comments on “Can a genetic test tell you if a medication will work?”

  1. Deanna Says:

    Thank you for addressing this. I am a pediatrician in Tennessee and often get questions about how MTHFR is the cause of my patients anxiety and depression. I have always thought genetic testing is a bunch of hogwash and good to hear that you agree.


  2. wzrd1 Says:

    While there are a few genetic tests where a confirmation is desired by a medical professional, those are extremely rare and other tests are also available and can provide a more rapid assay than genetic testing are available.
    I’m thinking specifically of instances like G6PD deficiency.
    Once, there was a question from doctor, who was concerned about prescribing chloroquine or not. I assured him that, although my heritage is 100% Sicilian rooted and hence, has the potential for the mutation, I’ve taken sulfa antibiotics and tolerated them well, was prescribed an antibiotic that was well tolerated that contained methylene blue and quite enjoy fava beans, so the drug will most likely we well tolerated and it was.
    Of course, these days, that drug isn’t very effective at times. :/

    I know that much. Figuring out G6PD deficiency vs 6PGD is for you doctors, I was only an SF medic, not a physician. Knowledge of favism was important in some regions, the latter, not as much. We also had physicians who specialized in our operations, frankly, I would never have been surprised then or now if one pulled out a Star Trek tricorder. Some of the mini lab kits they could pull out were nearly as impressive as that medical tricorder would be.
    And an order of magnitude more expensive than the usual hospital lab test would be.


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