Our observations show a higher colonic expression level of LRRK2 in PD patients compared to controls, especially in those with LRRK2 risk or mutation carriers, and the expression correlated with disease severity, suggesting that LRRK2 may be involved in the pathophysiology of PD in the very beginning of the disease process that is relevant to the host responses to altered gut microbiota observed in PD (Lin et al., 2019; Romano et al., 2021). Here, LRRK2 is linked to Parkinson disease.