They said their findings could lead to a treatment, but more immediately represent a warning to people with the genetic predisposition not to smoke.
The findings suggest that the disease in its many forms may stem from a common genetic defect that prevents the proper repair of lung injury, the researchers report in a forthcoming issue of American Journal of Respiratory and Critical Care Medicine.
IIP is a form of pulmonary fibrosis, a group of diseases characterized by scarring of the lungs. The condition, for which no treatment exists, typically kills its victims within five years. While the prevalence of the disease is unknown according the National Institutes of Health, estimates indicate the numbers are rising with as many as 15,000 new cases of idiopathic pulmonary fibrosis -- a form of the disease having unknown causes -- diagnosed yearly in the U.S.
After examining 111 families including multiple people with IIP, the Duke team found evidence that a single abnormal copy of an as-yet-unidentified gene can spark the disease. However, the condition appears to strike only those prone to the condition who also experience some secondary lung injury. Smokers, in particular, had over three times the risk of developing the condition than members of affected families who had never smoked, found the researchers.
"This is a terrible disease whose causes have remained unclear and for which no treatment exists," said Mark Steele, M.D. "Our findings provide convincing support for a genetic basis. But it's more than that -- development of the disease takes a second hit. One such hit is cigarette smoking."