The relationship between PD and IBD is much more controversial, since although gene association studies suggest that functional variants in the LRRK2 gene may confer shared effects on risk for Crohn's disease and PD, it has been also reported that PD as a whole is associated with lower risk of IBD (−15%) as well as of Crohn's disease (−17%) and ulcerative colitis (−12%) (114). Here, LRRK2 is linked to Crohn disease.