Diagram showing normal and abnormal CFTR channels in
epithelial cells. Courtesy of the Genetic Science Learning Center
at the University of Utah (USA).
Cystic fibrosis is an inherited disorder that is caused by an autosomal recessive mutation on human chromosome 7. Autosomal recessive means that each parent contributes a non-functional copy of the gene to the affected child. The probability that parents that are carriers of the mutation will have an affected child is 25%, and 50% that the child will be a carrier. This probability is constant for every subsequent child that the couple has.
The mutation results in a defective membrane chloride channel known as CTFR (cystic fibrosis transmembrane conductance regulator), which causes chloride and water transport in epithelial cells to malfunction. The faulty CTFR channel leads to the secretion of thick mucus that lodges in the lung, pancreas, and liver. These mucus plugs cause problems in each organ.
Lungs: Obstruction of bronchioles, along with enlargement (hypertrophy) and increase in the number (hyperplasia) of goblet cells.
Pancreas: Obstruction of pancreatic ducts, along with fibrosis of exocrine glands.
Liver: Obstruction of bile canals, leading to biliary cirrhosis.
Characteristics of cystic fibrosis include chronic lung disease causing a persistent and productive cough, pulmonary (lung) infections, bronchiectasis, bluish discoloration of the skin and mucus membranes (cyanosis), barrel-shaped chest caused by overuse of accessory muscles for respiration, rales (crackles), pancreatic insufficiency that causes greasy, foul-smelling stools (steatorrhea), malabsorption, abdominal pain, and infertility in males.
Clinical laboratory tests reveal oxygen deficiency (hypoxia), high concentrations of chloride in a sweat test, and an increased ratio of residual volume to total lung capacity.
Treatment involves the use of antibiotics to control infections, bronchodialators, techniques to clear airway secretions, and lung transplantation. The average age of survival is 31 years, as the affected individual eventually succumbs to pulmonary complications.
Additional Information about Cystic Fibrosis
What is Cystic Fibrosis? from the National Heart, Lung, and Blood Institute (USA)
Cystic Fibrosis from the Mount Sinai Medical Center (USA)
Chronic Obstructive Pulmonary Disease