A group of potentially fatal disorders affecting the lungs that includes lung fibrosis may be blamed on a person's inheritance, as well as his or her smoking habit, according to new research that evaluated dozens of families.1
Lung Inflammation and Scarring
The disorders are grouped in a class of diseases known as idiopathic interstitial pneumonia (IIP). Idiopathic pulmonary fibrosis (IPF) is one of the most common forms of these diseases. In the lungs, they cause widespread scarring known as fibrosis, as well as varying levels of inflammation in some cases.2
While the course and symptoms of these diseases can vary from person to person, lung inflammation is generally the most common manifestation in everyone. Inflammation can affect the bronchioles (small airways), the walls and air spaces of the lungs' air sacs, and the lungs' small blood vessels. Often, scarring occurs as a result of the healing of this inflammation. When fibrosis (scarring) builds up, the lung tissue's ability to transport oxygen becomes significantly compromised. A person's disability as a result of IPF is directly related to the amount of scarring that he or she has in the lungs.3
Cause and Symptoms
The key symptom of idiopathic pulmonary fibrosis is shortness of breath. It may progress to the point at which a person may find it hard to breathe even at rest. However, since this occurs in many different lung diseases, diagnosing IPF in these situations can often be difficult. Other symptoms may include a dry cough, or heart failure in the disease's later stages.3
What causes IIP isn't known. In some cases, pulmonary fibrosis can be caused by exposure to asbestos or metal dusts in the environment or workplace, a disease known as sarcoidosis that causes the formation of inflammatory cells, certain medications, exposure to therapeutic radiation, certain connective tissue diseases like rheumatoid arthritis, or a possible genetic inheritance.3
Pulmonary hypertension (PH) can be a life-threatening complication of pulmonary fibrosis in some cases. That's because the scarring that occurs contributes to blood vessel constriction in the lungs.4 PH is a form of high blood pressure in the pulmonary artery, which connects the heart to the lungs.
Shining Light on the Unknown
Now, this new study may offer some insight into the potential causes of IIP. "This study illustrates the important role that a specific environmental exposure, in this case, cigarette smoking, can play in the development of this type of lung disease among people who have a specific gene," explained David Schwartz, MD, director of the National Institute of Environmental Health Sciences (NIEHS) at the National Institutes of Health (NIH), and one of the study's investigators. "It once again underscores why people should not smoke."
The research team led by Mark Steele, MD, an assistant clinical professor of Medicine in the division of Pulmonary, Allergy, and Critical Care at Duke University, recruited 111 families for their study. At least two relatives in each family had been diagnosed with some form of IIP. In all, 309 people were affected with IIP and 360 were not.
For the research, each participant completed a detailed questionnaire asking them about their health status and exposure to certain environmental substances. They also underwent a range of tests, including a lung diffusion exam, which measures how well oxygen passes from the air sacs of the lungs into the bloodstream.
Genetics and Smoking Play Key Roles
Steele and his team then evaluated the data they collected in various ways. They looked to see if there was a relationship between cigarette smoking and familial interstitial pneumonia (FIP), a form of idiopathic pulmonary fibrosis with an inherited connection.5 This is the term used when at least two cases of IIP, such as idiopathic pulmonary fibrosis, occur in a family.
The researchers also wanted to know if there was, in fact, a genetic component to FIP. In addition to the fact that 111 families had at least two relatives with the disease, these people were diagnosed at similar ages and there was a similar risk for the disease among siblings, confirming the question about the genetic link.
Older people, men, and those who smoked also had a greater risk of developing FIP, the researchers found. After taking other factors into account that can increase the risk of developing the disease, the physicians concluded that smoking more than tripled the risk.
"We now know that a certain genotype [genetic factor] places someone at risk for this disease," said Steele. "Independent of genes, cigarette smoking also contributes to the development of this disease. The next step is to identify the specific gene or genes that cause the disease."
He noted that because this was the first study to focus on varying types of IIP within the same families, it could be possible that, in addition to genes, some environmental factor may also be responsible.
"These findings suggest that FIP may be caused by an interaction between a specific environmental exposure and a gene (or genes) that predisposes to the development of several subtypes of idiopathic interstitial pneumonia," Steele and his colleagues wrote.
1. Steele MP, Speer MC, Loyd JE et al. Clinical and pathologic features of familial interstitial pneumonia. Am J Respir Crit Care Med 2005 Nov 1;172(9):1146-52.
2. Garantziotis S, Steele MP, Schwartz DA. Pulmonary fibrosis: thinking outside of the lung. J Clin Invest 2004 Aug;114(3):319-21.
3. American Lung Association. Interstitial Lung Disease and Pulmonary Fibrosis. Available at: http://www.lungusa.org/site/pp.asp?c=dvLUK9O0E&b=35436. Accessed December 2, 2005.
4. Ramirez A, Varga J. Pulmonary arterial hypertension in systemic sclerosis: clinical manifestations, pathophysiology, evaluation, and management. Treat Respir Med 2004;3(6):339-52.
5. Vaclavik P. A rare occurrence of familial idiopathic pulmonary fibrosis. [Translated from Czech]. Vnitr Lek 1993 Jan;39(1):54-8.
John Martin is a long-time health journalist and an editor for CuraScript. His credits include overseeing health news coverage for the website of Fox Television's The Health Network, and articles for the New York Post and other consumer and trade publications.
