CFTR and cystic fibrosis: Intestinal obstruction in a null CF mouse model (C57BL/6J Cftr−/−) leads to high mortality (>80% [17]) by 40 days of age while lower rates of mortality [44] occur in a CF mouse model (C57BL/6JR117H/R117H) with a targeted knock-in of a missense mutation (p.Arg117His) associated with residual CFTR function [45], [46] and very low rates of MI in humans with CF [47].