Cystic fibrosis is caused by a mutation on the CFTR gene (cystic fibrosis transmembrane conductance regulator gene) on chromosome 7 (7q31.2). The CFTR gene is located on the long arm in the q31.2 region of chromosome 7. CFTR is an autosomal recessive gene. This means that you must inherit two defective genes, one from each parent, to have cystic fibrosis. A carrier of cystic fibrosis has one CFTR defective gene. A carrier of cystic fibrosis does not present with any symptoms of the condition, but he can pass on one defective gene to his offspring. A child has a 25 percent chance of inheriting the CFTR defective gene from both parents if both parents are carriers of cystic fibrosis. Cystic fibrosis is the most common genetic disorder, occurring in approximately one 1 of 3,000 live births.
There more than 1,000 possible mutations of the CFTR gene. Each mutation can lead to cystic fibrosis, but some mutations are more common than others. Approximately 70 percent of CFTR mutations are the result of a deletion of three base pairs of DNA. These DNA deletions result in the loss of amino acid phenylalanine in the CFTR protein at position 508: The most common CFTR mutation is also called delta F508.
A mutation of the CFTR gene causes defective chloride channels on cell membranes, which leads to an imbalance of chloride and water inside and outside cells throughout the body, including the lungs, airways, gastrointestinal system, pancreas and reproductive system. Cells with these malfunctioning chloride channels coat the lungs, pancreas and other major organs, resulting in excessively thick and sticky mucus. This thick mucus leads to blocked airways, lung inflammation, intestinal problems, reproductive issues and excessive chloride in sweat. These symptoms create lifelong health problems for cystic fibrosis patients.