A new gene association study has found a genetic link between Parkinson disease (PD) and Crohn's disease (a form of inflammatory bowel disease), suggesting the presence of shared disease mechanisms in these two disparate disorders. Researchers carried out exome sequencing and genotyping in individuals of Ashkenazi Jewish descent, including 2,066 individuals with Crohn's disease and 3,633 healthy controls. The team found functional gene variants in LRRK2 — the greatest known genetic contributor to PD — which conferred either increased risk or protection from Crohn's disease. A larger analysis of the LRRK2 locus in 24,570 people of Jewish and of non-Jewish descent, which included patients with Crohn's disease, patients with PD and healthy individuals, confirmed the presence of shared alleles that confer risk or protection in Crohn's disease and PD. The findings suggest commonalities in the underlying biology of these two conditions, which could have implications for the development of future treatments.