CFTR and cystic fibrosis: Baseline spheroid size varied with the underlying CFTR variant such that non-CF spheroids (0.124 ± 0.012 mm2) were larger than G551D (0.090 ± 0.012 mm2), Phe508del (0.047 ± 0.004 mm2), and PTC spheroids (0.016 ± 0.003 mm2) (mean ± SEM) (Fig. 3B).