Almost all of 1,500 different mutations so far identified in the CFTR gene in cystic fibrosis (CF) (MIM≠219700) or in related disorders (updates in the Cystic Fibrosis Mutation Database [4]) are single-nucleotide changes or small base pair(s) insertions or deletions in the exons or their flanking intronic sequences. This evidence concerns the gene CFTR and cystic fibrosis.