Although spontaneous colitis has not been described in animal models of NPC, several reasons suggest causality in human NPC1-IBD rather than mere coincidence: (1) the association of NPC1 with CD-like immunopathology but not UC, (2) the early paediatric onset of symptoms with severe phenotype and (3) the reproducible finding among many centres making a reporting bias very unlikely. Here, NPC1 is linked to inflammatory bowel disease.