Cystic fibrosis is a disorder that mostly affects the lungs. It is caused by a mutation in a gene called cystic fibrosis transmembrane conductance regulator (CFTR). As a result of this mutation, cells that produce mucus (a slimy substance like the one in your nose) secrete a thicker-than-normal mucus that can create blockages in the lungs and digestive system.
Read full article, here.