Mind the gap: Genetic knowledge and medical power

Since the completion of the Human Genome Project a decade ago, much excitement has swirled around the possibility that determining a person’s genetic makeup could help doctors personalize the diagnosis, treatment and prevention of disease. But James P. Evans, a physician and geneticist at the University of North Carolina at Chapel Hill, says the promises of genomic medicine have been overblown. He talked with Science News molecular biology writer Tina Hesman Saey about the hope and hype.

Even when we can define the sum total of an individual’s genetic risk for cancer and heart disease, that only gives us a very small part of the picture. UNC Lineberger Comprehensive Cancer Center

Will knowing a person’s genetic makeup make health care better?
There’s lots of excitement about the use of genetics and genomics in medicine, but the promise of that, I think, has been oftentimes misconstrued.

We’ve heard many claims that refining an individual’s risk for a variety of common diseases like heart disease and cancer will lead to better care for them, but there is frankly just no evidence that that is the case.

The risk factors for common diseases are predominantly not genetic. So even when we can define the sum total of an individual’s genetic risk for cancer and heart disease, that only gives us a very small part of the picture. Common diseases are, by definition, common. You can do all the fiddling and refining of an individual’s risk, and the fact is that these are such common diseases, things like cancer and heart disease, that even for individuals who are at relatively reduced risk as compared with the rest of the population, they’re still likely to die of those diseases. In other words, refining one’s relative risk for common diseases is meaningless in any practical terms because our absolute risk for those diseases is so high.

Secondly, we hear claims that by analyzing your risk for say heart disease and diabetes, that knowledge will motivate people to lead healthier lifestyles. There’s not a whit of evidence to suggest that. 

What is the real potential of genomic medicine?
Our burgeoning understanding of the genetic basis of disease will add immensely to our fundamental knowledge about those diseases. While it takes a long time to realize the practical benefits of such increased knowledge, that really is how science and how medicine works, and I think that we should not be too impatient and necessarily demand or expect tangible clinical outcomes in the near term. We need to get across to the general public that medicine and science move in incremental ways, and understanding more about these diseases will eventually pay off even if they don’t pay off immediately.

Our ability to sequence all of the genes in an individual or their entire genome will be a huge boon as a diagnostic tool to the small percentage of individuals who have diseases that result from discrete genetic [defects].

Another area that genomic medicine shows great potential in would be in the public health context. With these approaches, we now have the potential to identify asymptomatic individuals who are at high risk of preventable disorders — for example, that small percentage of people who have mutations that put them at high risk of breast cancer, colon cancer and lethal cardiac dysrhythmias. If you add up all the genes with mutations that lead to such dire risks you quickly get to 1 to 2 percent of the U.S. population walking around with such risks that are potentially identifiable by whole genome sequencing.

The other area in which I think there is tremendous potential is in carrier screening for rare autosomal recessive diseases. Right now when a woman or a couple is planning a pregnancy there are just vanishingly few genes in which mutations are common enough that it makes sense to say to that couple, “You know what? You could both have genetic testing.”

We now have reached the point with genomic analysis where we can in principle — and this is now being done by certain laboratories — say we’re going to take a look at hundreds of your genes that, when mutated, have a risk of a really, really bad disease in your offspring and we’re going to now offer you that so you can use that information, if you so desire, in family planning.

What can we do to make expectations more realistic?
We can simply insist that if a company says X, Y, Z will enhance your health and is a useful health tool then they need to have some evidence that that is the case. If people are interested in their genome and they want to spend the money for it, I think that’s great. I just think they deserve an honest accounting of its actual utility.

I think the press can help by restraining its understandable tendency to couch every advance in terms of breakthroughs and immediate clinical benefits. The other way to get around all this and avoid overhyping is to educate the public about how science really works.