CFTR and cystic fibrosis: It is necessary to obtain evidence of CFTR dysfunction through the identification of two CFTR gene mutations previously assigned as CF-causing, two tests showing a high Cl− concentration in sweat (>60 mEq/L), distinctive transepithelial nasal potential difference (NPD) measurements, and/or assessment of CFTR (dys)function in native colonic epithelia ex vivo [19,20,21,22].