24 Davies Davies JC JC Sheridan Sheridan H H Lee Lee P-S P-S Song Song T T Stone Stone A A Ratjen Ratjen F F Effect of ivacaftor on lung function in subjects with CF who have the G551D-CFTR mutation and mild lung disease: a comparison of lung clearance index (LCI) vs Effect of ivacaftor on lung function in subjects with CF who have the G551D-CFTR mutation and mild lung disease: a comparison of lung clearance index (LCI) vs spirometry. The gene discussed is CFTR; the disease is lung disorder.