The most commonly occurring mutation in people with cystic fibrosis is a deletion of a single codon. this results in

This deletion results in a polypeptide missing an amino acid. Cystic fibrosis is a genetic disease that affects mostly the lungs, but also other organs such as the pancreas and the liver. It is caused by a mutation in the gene cystic fibrosis transmembrane conductance regulator (CFTR). This mutation is a deletion of three nucleotides that cause the loss of the amino acid phenylalanine.

Carbon monoxide is the answer: )

Ithink its because more have died recently than in the past.