Cystic fibrosis is caused by mutations in which gene?

• A. BRCA1 gene
• B. CFTR gene
• C. HBB gene
• D. CFAP gene

Answer: (B)

Cystic fibrosis results from mutations in the CFTR gene, which encodes the cystic fibrosis transmembrane regulator, a chloride (and bicarbonate) channel on epithelial cell surfaces. When CFTR doesn’t function properly, chloride and water transport across the airway and other mucosal surfaces is disrupted, leading to very thick, sticky mucus that clogs airways and pancreatic ducts. This misregulated ion movement explains the characteristic lung infections and digestive problems seen in CF. Many different mutations in CFTR can impair the channel in ways that reduce its production, trafficking to the cell surface, or gating function, with autosomal recessive inheritance. The other genes listed are associated with different conditions—BRCA1 with DNA repair and cancer risk, HBB with beta-globin disorders like sickle cell disease, and CFAP genes with ciliary function—so they do not cause cystic fibrosis.