Among PD patients, the colonic LRRK2 level correlated with disease severity in both motor and cognitive function, and the expression levels were higher in those carrying LRRK2 risk or pathogenic variants than those with wild type LRRK2. Furthermore, PD patients in the prodromal phase had increased colonic LRRK2 expression compared to controls and, as the disease progressed, the expression of LRRK2 in colonic tissues progressively increased. This evidence concerns the gene LRRK2 and Parkinson disease.