Genetic testing can provide crucial information about what's causing a patient's problems and what lies ahead.
But for healthy patients? It's a lot tricker.
With the growing popularity of consumer genetic tests, patients are increasingly asking their doctors about whether a test could predict their vulnerability to certain conditions, such as cancer, dementia and heart disease. A case study published Monday in the Annals of Internal Medicine by researchers at Columbia University warns that doctors and patients alike should proceed carefully in understanding the context in which these tests provide useful information.
“Genetic testing was developed for diagnosing somebody who has a condition, or whose doctor suspects they have a condition,” said Ali Gharavi, MD, professor of medicine and chief of the Division of Nephrology at Columbia University College of Physicians and Surgeons and one of the article's authors.
In that case, doctors start with a prior suspicion of a condition that can be confirmed, he told Fierce Healthcare.
But with a healthy patient, the probability of a currently undiagnosed disease is lower, which makes the probability of a false-positive result higher, he said.
As a result, physicians may need to do additional work to confirm a diagnosis. The amount of additional work required depends on the degree to which a given genetic variance has been positively correlated with a specific condition.
A relatively small number of genetic mutations are both well-studied and well-understood. Certain cancer mutations, for example, correlate strongly with the risk of developing breast cancer or ovarian cancer. However, a positive result on those tests doesn’t mean an individual has one of these cancers, or even that they definitively will get them. Instead, it may simply indicate they have a higher risk of developing that cancer.
With other genetic mutations, potential variations could be falsely correlated with a disease or they could occupy a gray area classified as a “variant of unknown significance.” Labs tend to use this classification for variants that require more study before they can be classified either as benign or malignant.
Gharavi says it’s important for physicians to take the consequences of a potential false-positive into account when helping patients make a decision on whether or not to undertake a given genetic test.
“It’s probably better to whittle things down to what you’re concerned about—if you’re concerned about Alzheimer’s and you conduct a test that scans the entire genome and come back with variants of unknown significance for heart disease and cancer, et cetera, then suddenly your anxiety level goes much higher.”
For patients, Gharavi recommends talking to your doctor about the conditions best suited to a genetic test and ensuring you understand beforehand what the potential consequences of a positive test might be. And if the test comes up negative, remember that it doesn’t mean you have no risk of contracting the disease in question.
For practitioners, Gharavi suggests bearing in mind that not all genetic tests have the same predictive capability. Understanding which tests are well-studied and correlate with specific diseases can help provide patients the education they need to decide which tests they really want, given their family history or other specific concerns.
Since research is ongoing, physicians should be aware that it can be a lot of information to stay on top of. “It’s all changing very quickly, so conferring with a genetic counselor or clinical geneticist also helps—somebody who’s really familiar with these tests,” Gharavi advises.