CFTR and cystic fibrosis: After 1 month of ETI, sweat chloride (which reflects CFTR activity) decreased by an average of 39.0 mmol/L (95% CI: –41.4, –36.6), lung function increased by 8.9% predicted forced expiratory volume in 1 second (FEV1pp) (95% CI: 7.8%, 10.0%), body mass index (BMI) increased by 0.41 kg/m2 among adults (95% CI: 0.29, 0.53), and respiratory symptoms improved by 10.5 Cystic Fibrosis Questionnaire – Revised (respiratory domain) (CFQ-R RD) score points (95% CI: 7.5, 13.4; minimum significant change is considered 4 points, ref. 22) (Table 2), consistent with prior studies (1–4).