Over 2100 CFTR variants have been identified (Cystic Fibrosis Mutation Database: http://genet.sickkids.on.ca), of which approximately one-third have been confirmed as CF-causing since they result in functional expression defects of CFTR at the plasma membrane (PM) (Clinical and Functional Translation of CFTR: http://cftr2.org). This evidence concerns the gene CFTR and cystic fibrosis.