FOXI1 and cystic fibrosis: The level of MCC impairment in FOXI1-KO ferrets was also similar to CFTRG551D/G551D cystic fibrosis ferrets removed from treatment with a CFTR modulator (VX-770) that corrects the gating defect in the CFTRG551D channel (Fig. 1i,j and Supplementary Video 2).