Encoded Maladies, A Survey of Disorders that Arise in Our Genes: Cystic fibrosis

By Ian MacArthur
 
Anyone who has ever suffered from the common cold understands the nuisance posed by mucous buildup in the upper respiratory tract. Although it may cause discomfort, mucous plays an important role in the body’s defense by trapping pathogens that seek access to tissues and then excreting them by way of a sneeze or cough. While the seasonal stuffy nose or sinus infection caused by mucous buildup is unwelcomed by all, these conditions become particularly critical for patients of cystic fibrosis, a genetic disorder characterized by the abnormal production of mucous that blocks respiratory, digestive, and reproductive tracts. 
 
Cystic fibrosis (CF) is caused by a mutation to the CFTR gene located on chromosome 7. Short for cystic fibrosis trans-membrane conductance regulator, CFTR codes for a chloride ion channel protein responsible for the transport of chloride ions into and out of epithelial tissues. Additionally, CFTR is responsible for the regulation of sodium ion channels that are important in the function of the pancreas and lungs. The deletion of the three nucleotide codon for the amino acid phenylalanine inhibits the function of the CFTR protein in about 70% of CF cases, although over 1,000 different mutations have been identified.  The dysfunctional CFTR protein is unable to properly regulate the ionic concentrations of cells that produce sweat, saliva, and mucous. Because chloride and sodium ion concentrations are essential for the proper flow of water in these tissues, mucous secretions are not properly hydrated, causing them to be thick and sticky.
 
The thick secretions of mucous have disastrous effects on the bodies of CF patients. Mucous buildup in the lungs can block air passageways, making breathing difficult and leaving patients prone to potentially fatal bacterial infections. Additionally, mucous may block passages in the pancreas that may lead to severe digestive problems, as well as reproductive ducts that often cause infertility. Recurrent cases of pneumonia are associated with the respiratory effects of CF, in addition to fatigue and constant coughing and sinus blockages.
 
Cases of cystic fibrosis can be found in all ethnic groups, although the illness has the highest incidence among Caucasians in the United States, specifically those ancestrally hailing from Northern and Central Europe. CF is inherited recessively, and consequently millions of people carry the gene for the disorder without ever developing symptoms. It is estimated that nearly 1 in 30 Caucasians in the United States is a carrier of a mutated CFTR gene, and that the disease currently affects approximately 30,000 Americans.

Although there is currently no cure for cystic fibrosis, a number of treatments exist that help patients effectively cope with symptoms. Antibiotics are administered to cure sinus infections and to treat bacterial pneumonia, and mucous can be removed periodically from the respiratory tracts of patients via suction and other methods. A specialized diet is required to counteract digestive problems that may arise, and vitamin and enzyme supplements can also aid in this capacity. The average life expectancy of CF patients is between thirty to forty years, with death commonly caused by respiratory problems. Though this may appear a grim prognosis, most patients are able to lead healthy lives well into adulthood, and increased life expectancy for patients over time demonstrates progress in treating the disease. As our proficiency in treating the illness advances, it is possible that someday the condition need not bound the lives of CF patients.