FLCN is a gene that helps to control cell growth and structure in certain parts of the body.
Everyone has two FLCN genes (one from their mother, and one from their father). If one of the genes is not working, this is known as having a faulty FLCN gene, or having a FLCN mutation. People with a faulty FLCN gene are known to have Birt-Hogg-Dubé syndrome.