More than 2000 CFTR variants have been recorded so far worldwide (http://www.genet.sickkids.on.ca/app, accessed on 26 February 2023) although to date only 401 CFTR variants are known to be CF-causing (https://cftr2.org/, accessed on 26 February 2023) on the basis of functional studies. This evidence concerns the gene CFTR and cystic fibrosis.