To date, four CFTR-directed modulators have reached the market for the treatment of CF patients carrying specific CFTR mutations (Ramsey et al., 2011; De Boeck et al., 2014; Wainwright et al., 2015; Rowe et al., 2017a; Taylor-Cousar et al., 2017; Heijerman et al., 2019; Middleton et al., 2019). The gene discussed is CFTR; the disease is cystic fibrosis.