CFTR and exocrine pancreatic insufficiency: In order to gain a better understanding of the effect of CF mutations on CFTR function, and especially why some patients carrying some rare, or very rare, mutations only develop severe symptoms later in life, we examined the functional and cellular consequences of the rare missense mutation, W361R, and compared it to F508del-CFTR, and another class 2 CF mutation, L69H, which causes a severe CF phenotype with pancreatic insufficiency and congenital bilateral absence of the vas deferens (CBAVD) (Sharma et al., 2015).