CFTR and cystic fibrosis: Of the 2000 cataloged mutations, approximately 40% of them result in single amino acid substitutions, 36% of them result in RNA processing errors (nonsense, missense, and frameshift), 14% are neutral variants, and the remainder are made up of undefined outcomes, rearrangements of CFTR, or promoter problems.53 In the north European Caucasian, the most common CF causing mutation is ΔF508, with a reported 70%–76% of patients having this Class II mutation.