CFTR and cystic fibrosis: The three mutations we studied affect approximately 1.5% of individuals with CF and do not disrupt the classical canonical splicing regions [20], rather they cause CF by creating strong alternative splice sites which result in formation of pseudoexons or extend existing exons in CFTR. The first mutation, c.1679+1634A>G, creates a very strong splice acceptor in intron 12 of CFTR with 99% of transcripts containing a 49bp pseudoexon with an in-frame TAA stop codon in the pseudoexon causing premature termination of the CFTR protein [21], and is classified as a severe CF-causing mutation.