Cystic Fibrosis Overview


Cystic Fibrosis is an autosomal recessive inherited disease affecting the lungs and digestive system. A defect of a chloride channel leads to extremely thick mucus secretions, which congest the airways and ducts of the GI tract.

It is typically caused by defects in the CFTR gene on chromosome 7, which encodes a transmembrane chloride channel. The most common mutation is a deletion of phenylalanine at position 508 (Phe508). This deletion causes misfolding of the chloride channel, which is then retained in the RER instead of being transported to the plasma membrane.

Since CFTR works to reabsorb chloride at the skin, patients with CFTR have increased sweat chloride, a finding which is often used as a common diagnostic test for cystic fibrosis. Contrastingly, CFTR works to secrete chloride in the GI tract, leading to eventual secretion of sodium and water. As such, defects in CFTR can lead to deficiencies in pancreatic duct secretions (see Cystic Fibrosis Complications - coming soon!).

Other test results pointing to a diagnosis of cystic fibrosis include increased blood trypsinogen on neonatal screening, as well as a negative transepithelial potential difference.

Find this Cystic Fibrosis Overview and other Genetic Disorder mnemonics among Pixorize's visual mnemonics for the USMLE Step 1 and NBME Shelf Exams.