One family with rare gene mutation gives clues to preventing heart attacks.
Patients with mutations that disable a gene called ANGPTL3 have extremely low levels of cholesterol in the bloodstream. They also show no evidence of plaque in the coronary arteries, suggesting the mutations protect against heart attacks. Studying such patients can help guide drug development with the goal of preventing heart attacks.

A new study of such “beneficial” genetic mutations, led by Washington University School of Medicine in St. Louis, may provide guidance on the design of new therapies intended to reduce the risk of heart attacks.

The study was published March 29 in the Journal of the American College of Cardiology.

The researchers studied members of a family with rare mutations in a gene called ANGPTL3. The gene is known to play important roles in processing lipoproteins, molecules that package and transport fat and cholesterol through the bloodstream. Partial or complete loss of this gene was known to cause low cholesterol and triglyceride levels in the bloodstream. But whether it affects risk of heart attack was unclear.

Three of these family members – those with a complete loss of this gene – showed extremely low blood cholesterol and no evidence of plaque in their coronary arteries. According to the study authors, it was noteworthy that one of these patients showed no evidence of atherosclerosis despite having high risk factors for it, including high blood pressure and a history of type 2 diabetes and tobacco use.

“The family members with complete loss of ANGPTL3 have extraordinarily low cholesterol,” said first author Nathan O. Stitziel, MD, PhD, an assistant professor of medicine and of genetics. “The interesting thing about this family is the individuals with total loss of this gene had siblings with normal copies of the same gene. So we could compare people with differences in the function of this gene who are otherwise closely related genetically and share similar environments. It’s an anecdotal study of one family, but we felt it might provide some insight into the effects of blocking ANGPTL3.”

While the individuals with nonfunctional copies of the gene showed no coronary plaque, their siblings with working copies of the gene showed evidence of plaque in the coronary arteries, though it was not yet causing symptoms — a situation that is common in the general population, according to Stitziel.

To study the gene beyond the experience of a single family, the scientists also analyzed data available from large population studies. In data from one study of about 20,000 patients, the researchers found those with a partial loss of this gene had, on average, 11 percent lower total cholesterol, 12 percent lower LDL cholesterol, and 17 percent lower triglycerides, measured in the blood, than individuals with full gene function.

Analysis of data from other large population studies showed a link between partial loss of the gene and a lower risk of coronary artery disease and an association between lower circulating levels of ANGPTL3 protein and a lower risk of heart attack.

Taken together, these findings provide support for efforts to develop drugs that inhibit ANGPTL3 in order to reduce the risk of coronary artery disease and heart attack. The same reasoning led to the development of a class of drugs known as PCSK9 inhibitors, which have recently been shown to be effective at reducing the risk of heart attack in a large clinical trial of more than 27,000 men and women.