Previous studies have demonstrated that sphingosine is abundantly expressed on the luminal side of nasal to bronchial epithelial cells in wild-type mice, while sphingosine is greatly reduced in epithelial cells of cystic fibrosis (CF) patients and mice, due to reduced activity of the acid ceramidase in CF epithelial cells8,9,12. Here, ASAH1 is linked to cystic fibrosis.