Birt-Hogg-Dubé syndrome (BHDS, MIM 135,150), or Hornstein-Knickenberg syndrome, is an autosomal dominant hereditary disorder associated with a germline pathogenic variant folliculin (FLCN), which increases risk of benign cutaneous fibrofolliculomas, pulmonary cysts, spontaneous pneumothorax, and multiple, mainly malignant, bilateral and multifocal renal neoplasias. This evidence concerns the gene FLCN and Spontaneous pneumothorax.