A number of proteins encoded by PD risk such as leucine-rich repeat kinase 2 (LRRK2) and glucocerebrosidase (GCase) and highly expressed in peripheral monocytes, and in the case of the main familial PD risk gene LRRK2, there is overlapping genetic risk with inflammatory bowel disease and the susceptibility to bacterial infection [10,11]. Here, LRRK2 is linked to Parkinson disease.