Cystic fibrosis

Cystic fibrosis is a serious genetic disease that occurs in about one of about every 4,000 births. It's caused by a faulty gene that regulates ion flow in several semi-permeable tissues in the body, such as the lungs, sinuses, and intestines. The faulty gene must be inherited from both parents and a single faulty gene will not cause any symptoms.
Fibrosis patients suffer from numerous disorders of the lungs and digestive tract. Primary among these is inflammation of the lungs which results in large amounts of thick mucous which both interferes with air flow and provides a breeding ground for infection. As such, they frequently suffer from bouts of pneumonia and often have to be given antibiotics at the first sign of infection.
Treating fibrosis is difficult, requiring pharmaceutical intervention as well as daily physical therapy. However, despite rigorous intervention, patients rarely live to be 40 and most die in their 20s from complications related to the disease.