Can genetic testing predict risk of heart disease?
We've all heard that bad things happen to good people -- and that includes heart attacks occurring in people who have minimized their risk factors.
Even someone who does everything right can develop heart disease if he or she is predisposed to the one critical factor that can't be controlled -- genetics. To such an individual, a heart attack would come as a surprise, even though from the viewpoint of heredity, the event was already "in the cards."
But what if there was a way to test for a genetic predisposition to heart disease using a person's DNA?
There is. It's called genotyping -- but it's as yet experimental and controversial.
Every human being is unique thanks to variations in genes that make up the genome -- the complete menu of coded instructions that make us who we are. Some variations can make us susceptible to certain diseases, or even dictate how well we respond to certain medications (for example, a person might have a sensitivity to blood thinners) or if we're likely to become bald.
Researchers have been able to identify certain "markers" that are associated with disease. The theory behind genotyping is that the presence or absence) of these markers can be used to determine if someone might be carrying an otherwise unseen risk buried in the genetic code.
Such a test could spare hundreds of thousands of Americans from getting angiograms, an expensive procedure to check for clogged arteries. Most of these -- usually performed in a cardiac cath lab -- turn out negative, putting the patient at needless risk.
With a simple blood or saliva sample, which is all a genetic test requires, angiograms could be avoided if the patient doesn't have the markers associated with heart disease. Likewise, someone who has no other risk factors -- but shows the markers -- could take early precautions.
While the theory sounds simple, the practical application is complicated.
Accurate genotyping is still evolving. For all researchers know, there is much they don't. For example, they're still in the dark about both the rare and common variants that contribute to heart disease.
The typical test is not comprehensive, either. Genotyping, which is the process of determining an individual's genetic variants, is a far cry from the depth of sequencing the entire genome. It's also not nearly as expensive. Private companies that offer whole genome sequencing may charge as much as $100,000 -- compared to the $300 to $1,100 they charge for genotyping.
There is no evidence these tests can predict a person will acquire heart disease -- or even the risk of it occurring. Although the test itself is better than 99 percent accurate, there is debate as to how the results should be interpreted. Some rare genetic variants can increase the risk of disease by several hundred percent -- but most of those tested by private companies increase the risk by only 2 or 3 percent.
In addition, some people will get different results from different genotyping companies.
One patient with multiple sclerosis was considered unlikely to get the disease, and had no abnormal risk of heart disease in spite of a family history of it -- and having a heart attack at age 50.
Cardiologists weigh several factors when assessing a patient's risk of heart disease -- such as high blood pressure, high cholesterol, lack of exercise, smoking, diabetes and family history. This last is difficult to obtain accurately because it is self-reported. Also, a patient who claims to have no family history of heart disease may still have inherited the genes that increase risk. A patient's parent may be young enough that the disease hasn't yet presented at the time the patient is being tested.
The hope of the future is that genotyping can accurately predict the onset -- or even risk -- of heart disease. But it's not there yet.
For now, it may be helpful as part of a battery of tests, providing a cardiologist with yet one more piece of vital information to furnish a more accurate diagnosis.