Scientists studying a rare genetic disorder have made a surprising discovery that helps explain why certain heart tumors develop and suggests they may be more common than had been believed.
Doctors should look more broadly for signs of such tumors, which aren't cancerous but are dangerous because they can break off and cause strokes, researchers say.
``This may be more widespread than we had ever thought,'' said Dr. Jil Tardiff, a cardiologist at Albert Einstein College of Medicine in New York who reviewed the research that was reported in Thursday's New England Journal of Medicine.
The work was led by Dr. Craig Basson, a cardiologist at Weill Medical College of Cornell University, and involved four other hospitals in the United States and two in Belgium.
They studied a large Belgian family with 18 members who had a muscle disorder that caused spotty skin pigmentation, tight or clenched hands and feet, and an inability to open their jaws fully. Three also had heart tumors called myxomas, which affect one of every 100,000 people each year.
``Anybody who's a cardiologist has seen one,'' Basson said of such tumors.
No one had connected them to muscle disorders, but Basson suspected a link. He surprisingly found it in myosin, a group of proteins with an array of important jobs, including making muscles contract.
Defects in myosin genes are known to cause disorders such as Usher syndrome, the leading cause of blindness and deafness in young children. A decade ago, they were linked to sudden cardiac death in young people.
The gene defect Basson identified is very similar to some of the mutations that cause sudden cardiac death _ an ``unexpected and exciting'' discovery, Tardiff wrote.
``It makes us think more broadly'' about who may have heart tumors, and to suspect the condition in people with other muscle disorders or unusual orthopedic symptoms like the clenched hands, Tardiff said. ``Many people think it's underdiagnosed.''
Now that the cause of such tumors is known, scientists can try to design treatments like drugs and gene therapy as alternatives to surgery, the only treatment for them now, Basson said.
The discovery also could have implications for the field of stem cell biology. The myosin defect Basson identified is in a gene that was thought to stop functioning shortly after birth. His work shows it may keep going to some degree in some people, which he views as evidence that there's a type of stem cell in the adult heart, a widely debated theory.
The National Institutes of Health funded the study.