Moreover, based on our data showing good correlations of CFTR-mediated Cl− secretion with absolute FEV1 values and FEV1 decline rate (Fig. 3), as well as taking into account our discriminant analyses (Fig.4) demonstrating that CFTR-mediated Cl− has the highest discriminant power (90.4%) to distinguish among Classic CF, Non-Classic CF and Non-CF groups, we propose that colonic CFTR-mediated Cl− secretion, perhaps together with sweat-Cl−, may be the best biomarker in clinical trials aimed at modulating CFTR [44], [48]. The gene discussed is CFTR; the disease is cystic fibrosis.