Birt–Hogg–Dubé syndrome (BHD), also Hornstein–Birt–Hogg–Dubé syndrome, Hornstein–Knickenberg syndrome, and fibrofolliculomas with trichodiscomas and acrochordons is a human autosomal dominant genetic disorder that can cause susceptibility to kidney cancer, renal and pulmonary cysts, and noncancerous tumors of the hair follicles, called fibrofolliculomas. The symptoms seen in each family are unique, and can include any combination of the three symptoms. Fibrofolliculomas are the most common manifestation, found on the face and upper trunk in over 80% of people with BHD over the age of 40. Pulmonary cysts are equally common (84%), but only 24% of people with BHD eventually experience a collapsed lung (spontaneous pneumothorax). Kidney tumors, both cancerous and benign, occur in 14–34% of people with BHD; the associated kidney cancers are often rare hybrid tumors. Any of these conditions that occurs in a family can indicate a diagnosis of Birt–Hogg–Dubé syndrome, though it is only confirmed by a genetic test for a mutation in the FLCN gene, which codes for the protein folliculin. Though its function is not fully understood, it appears to be a tumor suppressor gene that restricts cell growth and division. Versions of FLCN have been found in other animals, including fruit flies, German Shepherds, rats, and mice. The disease was discovered in 1977, but the connection with FLCN was not elucidated until 2002, after kidney cancer, collapsed lungs, and pulmonary cysts were all definitively connected to BHD. Birt–Hogg–Dubé syndrome can manifest similarly to other diseases, which must be ruled out when making a diagnosis. These include tuberous sclerosis, which causes skin lesions similar to fibrofolliculomas, and Von Hippel–Lindau disease, which causes hereditary kidney cancers. Once diagnosed, people with BHD are treated preventatively, with monitoring of kidneys and lungs using medical imaging. Fibrofolliculomas can be removed surgically and pneumothorax and kidney cancer are treated according to the normal standard of care. Dermatologic examinations, neck ultrasounds and colonoscopies should be considered as well . Signs and symptoms Skin Birt–Hogg–Dubé syndrome affects the skin and increases the risk of tumors in the kidneys and lungs. The condition is characterized by multiple noncancerous, dome-shaped tumors of the hair follicles (fibrofolliculomas), particularly on the face, neck, and more rarely, the upper chest. The fibrofolliculomas are generally described as having an opaque white color or a yellowish tone and have a waxy, smooth texture. The tumors are always found on and around the nose and on and behind the outer ear. Typically,