Cystic fibrosis (CF) is a group of conditions variable in severity and mainly affecting the upper respiratory system. It is the most common fatal inherited disease and can be traced to a single recessive gene. Improved therapy has transformed CF from a disease characterized by death in early childhood to a chronic illness, with most patients living to adulthood. But despite this progress, there still is no cure for the disease and most patients eventually succumb to infections of the airways and lung failure.
CF affects tissues that produce mucous secretions, such as the airway, the gastrointestinal tract, the ducts of the pancreas, the bile ducts of the liver and the male urogenital tract. CF alters the chemical properties of mucous; it becomes thick and sticky and instead of protecting tissues from harm, the abnormal mucous obstructs the ducts and airways, causing tissue damage. The thick CF mucous also obstructs the pancreas, preventing enzymes from reaching the intestines to help break down and digest food. Because the mucous provides an ideal breeding ground for many microorganisms, CF patients have frequent airway infections, the most common being from Pseudomonas bacteria. Recurring Pseudomonas infection and the inflammation that accompanies it gradually damage the lungs, causing respiratory failure, which is the leading cause of death among CF patients.
The symptoms and severity of CF vary from patient to patient. For example, not all CF patients suffer from impaired pancreatic function. The degree of lung disease also varies. Some of this variation can be attributed to differences in the specific genetic defects in different patients, but even patients with identical mutations may have very different severities of disease. Even siblings with the same genetic defect who share other genetic traits can have different CF manifestations. Therefore, although the specific mutation in the CF gene contributes to the course of the disease, other differences in the individual genetic makeup, and perhaps in the environment, also play a role.
The defective cystic fibrosis gene is carried by 1 in every 20 Caucasians, on average. These carriers do not have symptoms of CF. The condition is only expressed if a person inherits a copy from both parents, a risk for every 1 in 2,000 to 3,000 live births, depending on the country, making CF one of the most common lethal genetic diseases in Caucasians. The incidence is lower in other racial groups.
Cystic fibrosis affects approximately 30,000 children and adults in the USA. 1,000 children with CF are born every year in the USA, of which one quarter will not survive beyond adolescence. According to the U.S. CF Foundation, one half of all individuals with CF die before the age of 31.