Chromosome 7
CFTR stands for Cystic Fibrosis Transmembrane Conductance Regulator. It is a chloride ion channel protein found in cell membranes throughout the body, particularly in the lungs, pancreas, and intestines. Mutations in the CFTR gene cause cystic fibrosis, one of the most common inherited genetic disorders.
Genetic information flows from DNA to mRNA to protein. Mutations at the DNA level can change the final protein product.
Three nucleotides are deleted, removing phenylalanine at position 508. The protein misfolds and cannot reach the cell membrane.
CFTR channels in the phospholipid bilayer allow chloride ions to cross. Without functional channels, water balance is disrupted and thick mucus builds up.
Cholera toxin works by forcing CFTR channels to stay permanently open, causing massive loss of chloride ions and water from intestinal cells. This leads to severe diarrhea and dehydration. Interestingly, people who carry one copy of the deltaF508 mutation (heterozygous carriers) may have some resistance to cholera because they have fewer functional CFTR channels available for the toxin to exploit. This is an example of heterozygote advantage, which may explain why the CF mutation has persisted in human populations.