Cystic Fibrosis Health Article

Definition

Cystic fibrosis (CF) is an inherited disease that affects the lungs, digestive system, and sweat glands, and causes infertility in males. Its name derives from the fibrous scar tissue that develops in the pancreas, one of the principal organs affected by the disease.

Description

Cystic fibrosis affects the body's ability to move salt and water in and out of cells. This defect causes the lungs and pancreas to secrete thick mucus, an inflammatory response that blocks passageways—particularly airway passages—and therefore prevents proper functioning of the affected areas.

CF affects approximately 30,000 children and young adults in the United States, where approximately 3,000 babies are born with CF every year. CF primarily affects people of white northern-European descent. Rates of CF are much lower in nonwhite populations.

Many of the symptoms of CF can be treated with drugs or nutritional supplements. Close attention to and prompt treatment of respiratory and digestive complications have dramatically increased the expected life span of a person with CF. Several decades ago, most children with CF died by the age of two years. By the end of the twentieth century, about one-half of all people with CF lived past 31 years of age. That median age is expected to grow as new treatments are developed. It is estimated that a person born in 2001 with CF has a median expected life span of about 40 years.

Genetic profiles

Cystic fibrosis is a genetic disease, meaning it is caused by a defect passed on through the genes. Genes, found in the nucleus of all body cells, control cell function by serving as the blueprint for the production of proteins. Proteins carry out a wide variety of functions within cells. The cystic fibrosis transmembrane conductance regulator (CFTR) gene, when defective, causes CF. A simple defect in this gene leads to all the consequences of CF. There are more than 500 known defects in the CFTR gene that can cause CF. However, mutation delta F508 in exon 10 is present in about 70% of CF chromosomes worldwide.

Genes can be thought of as long strings of chemical words, each made of chemical letters called nucleotides. Just as rearranging its letters can change a word and changing a word can change a sentence, genes can be mutated, or changed, by changes in the sequence of their nucleotide letters. The gene defects in CF are called point mutations, meaning that the gene is mutated only at one small spot along its length. In other words, the delta- F508 mutation is a loss of one "letter" out of thousands within the CFTR gene. As a result, the CFTR protein made from its blueprint is made incorrectly and cannot properly perform its function.

The CFTR protein helps to produce mucus. Mucus is a complex mixture of salts, water, sugars, and proteins that cleanses, lubricates, and protects many passageways in the body, including those in the lungs and pancreas. The role of the CFTR protein is to allow chloride ions to exit from mucus-producing cells. When the chloride ions leave these cells, water follows, thinning the mucus. In this way, the CFTR protein helps to keep mucus from becoming thick and sluggish, thus allowing the mucus to be moved steadily along the passageways to aid in cleansing.

In CF the CFTR protein does not allow chloride ions out of the mucus-producing cells. With less chloride leaving, less water leaves, and the mucus becomes thick and sticky. It can no longer move freely through the passageways, so they become clogged. In the pancreas, clogged passageways prevent secretion of digestive enzymes (including insulin) into the intestine, causing serious impairment of digestion, especially of fats, which may lead to malnutrition. Mucus in the lungs may plug the airways, preventing good air exchange and, ultimately, leading to emphysema or COPD. The mucus is also a rich source of nutrients for bacteria, leading to frequent infections such as sinusitis, bronchitis, and gastritis.