CFTR and cystic fibrosis: Reduced first, second, and amplifying phase secretion in CF islets have been reported by numerous researchers (Sun et al., 2017; Kelly et al., 2019); however, it was found that serum insulin level of CFTR–/– mice showed no significant difference than WT and HET mice by ELISA (Figure 1D), indicating that the amount of insulin secretion by CFTR–/– mice was normal before CFRD.