More than 750,000 people in the United States have dilated cardiomyopathy, a potentially life-threatening condition in which the heart’s main pumping chamber, the left ventricle, enlarges and grows increasingly weak. Research has shown that 1 in 10 people with this condition were born with a mutation in the TTN (titin) gene, but, until now, it has been unclear whether everyone with these mutations will inevitably develop dilated cardiomyopathy.

In a new study published in Circulation, researchers at Penn Medicine and Geisinger reviewed gene sequences of more than 70,000 people, and found that 95% of patients who had the genetic mutations did not have heart disease or signs of cardiac decline. However, they did find subtle differences in the hearts’ ability to pump efficiently, compared to those without the mutation.

“It’s clear that these gene mutations have a real effect on one’s heart, and yet, there are a lot of people carrying the deleterious mutations right now who are fine,” says the study’s corresponding author Zoltan Arany, a professor of cardiovascular medicine in the Perelman School of Medicine. “While our study moves us one step closer to being able to predict, based on one’s genes, who will get this disease, there is still a difference between these two populations that we don’t yet understand. The next step will be to identify the specific variable causing some of these patients to get heart disease.”