Cystic fibrosis, also called mucoviscidosis, is an autosomal recessive genetic disorder of the viscous secretions in the body. In turn, it effects the lungs, pancreas, liver, and intestines, as well as all other exocrine glands in the body. The most common genetic mutation that causes CF is a deletion of three nucleotides that results in a loss of phenylalanine, an amino acid at the 508th position on the protein. It should be noted, however, that there are over a thousand other mutations that can produce CF. A certain gene mutation can affect how the cystic fibrosis transmembrane conductance regulator protein works. CFTR acts as a channel protein that controls the passage of chloride and sodium in and out of cells with epithelial membranes. When it is working properly, the ions flow freely in and out of the cells. When the channel is blocked or not working, the ions cannot flow out. In the lungs, CFTR regulates the flow of water and chloride ions through cells, so when it is not working, it creates a buildup of thick mucus in the lungs. The protein is also found in sweat glands; there, it is responsible for controlling movement of chloride and thiocyanate. When it does not work, the molecules are trapped inside the cells of the airway and outside in the skin. Because chloride is negatively charged, it changes the electrical potential in and out of the cell, which then causes cations–such as sodium–to cross in.
The most common signs and symptoms of cystic fibrosis are salty tasting skin, poor growth and lack of weight gain despite a normal food intake, bowel obstructions, frequent chest infections and lung disease, and coughing or shortness of breath. Symptoms often appear in infancy and childhood. Lung disease results from clogging of the airways, decreased ability of the cilia to clear the excess mucus, and resulting inflammation. Infections often become worse due to the normal bacteria that live in the thick mucus growing out of control and causing pneumonia. Other symptoms include coughing up blood, pulmonary hypertension, heart failure, hypoxia, and respiratory failure requiring support with breathing masks, such as bilevel positive airway pressure machines or ventilators. Mucus in the paranasal sinuses is equally thick and may also cause blockage of the sinus passages, leading to infection. Common gastrointestinal problems include pancreatitis, due to the thickened pancreatic secretions that block exocrine movement of digestive enzymes into the duodenum. The lack of digestive enzymes also leads to malabsorption of nutrients. The liver can also be affected due to the bile secretion blocking the ducts they pass through, which ultimately leads to cirrhosis.
Means of diagnosing cystic fibrosis include newborn screening, sweat testing, and genetic testing. While there are no cures for cystic fibrosis there are several treatment methods, and the prognosis for patients with CF has improved greatly. The foundations of proper management are proactive treatment of airway infection and encouragement of good nutrition and exercise. Antibiotics may be given orally, intranasal, or intravenously to kill the infection. BiPAP machines or other ventilator-assist devices may be helpful in getting more adequate air movement in these patients. Pulmonary rehabilitation throughout the patient’s life is aimed at maximizing organ function, and therefore quality of life. At best, current treatments delay the decline in organ function. However, lung transplants are common in patients with CF after their lung function has drastically declined.
Image Caption: “Clubbing” of the fingers is a classic features of Cystic Fibrosis, although not present in many patients. Credit: Jerry Nick, M.D./Wikipedia (CC BY 3.0)