The CARD15 gene known to be associated with Crohn's disease is over-represented in patients with PD [29]; vice versa, the Leucine-rich repeat kinase 2 (LRRK2) gene, a causative PD mutation, was recently identified as a major susceptibility gene for Crohn’s disease by genome-wide association studies [30]. The gene discussed is NOD2; the disease is Parkinson disease.