However, data on the degree of in vivo correction of CFTR protein expression by ELX/TEZ/IVA—as a highly potent modulator treatment which permits treatment of the majority of affected patients with CF, achieving impressive clinical effects (Heijerman et al., 2019; Middleton et al., 2019)—have remained elusive. The gene discussed is CFTR; the disease is cystic fibrosis.