CFTR and cystic fibrosis: More than 2100 different mutations are known in the CFTR gene, of which only a minority has been studied in detail (cystic fibrosis mutation database: http://www.genet.sickkids.on.ca/app, accessed on 6 July 2021; CFTR2 project: http://cftr2.org, accessed on 6 July 2021) [3].