CFTR and cystic fibrosis: First, at the mRNA level, while 74% of CFTR transcripts are derived from the integrated SE23–27, the overall level of such transcripts is most likely very low as CFTR transcripts that skip the integrated superexon and splice to the W1282X-containing exon 23 will be subject to NMD which occurs at higher level for W1282X relative to many other CF-causing variants [26].