Birt-Hogg-Dubé syndrome is a rare disorder that affects the skin and lungs and increases the risk of certain types of tumors. The condition is characterized by multiple noncancerous (benign) skin tumors, particularly on the face, neck, and upper chest. These growths typically first appear in a person's twenties or thirties and become larger and more numerous over time. Affected individuals also have a higher chance of developing cysts in the lungs and an abnormal accumulation of air in the chest cavity (pneumothorax) that may result in the collapse of a lung. Additionally, people with Birt-Hogg-Dubé syndrome have an increased risk of developing cancerous or noncancerous kidney tumors and possibly tumors in other organs and tissues.

Birt-Hogg-Dubé syndrome is very rare; the exact incidence is unknown. This condition has been reported in more than 60 families.

Mutations in the FLCN gene cause Birt-Hogg-Dubé syndrome.
The FLCN gene provides instructions for making a protein called folliculin. The normal function of this protein is unknown, but researchers believe that it may act as a tumor suppressor. Tumor suppressors prevent cells from growing and dividing too rapidly or in an uncontrolled way. Mutations in the FLCN gene may interfere with the ability of folliculin to restrain cell growth and division, leading to the formation of noncancerous and cancerous tumors. Researchers have not determined how FLCN mutations increase the risk of lung abnormalities, such as a pneumothorax.

This condition is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. In some cases, an affected person inherits the mutation from one affected parent. Other cases may result from new mutations in the gene and occur in people with no history of the disorder in their family.

Researchers believe that two copies (instead of one copy) of the FLCN gene must be altered for a person to develop the kidney tumors often seen in Birt-Hogg-Dubé syndrome. People with this condition are born with one mutated copy of the FLCN gene in each cell. Then, during their lifetime, the other copy of the gene is mutated in kidney cells. These genetic changes disable both copies of the FLCN gene, which allows the cells to divide uncontrollably and form tumors.