COMT and irritable bowel syndrome: Canonical correspondence analysis showed that PD severity index (UPDRS total score) was positively correlated with the disease duration, dysphagia, and the use of COMT inhibitor or amantadine, whereas age, Bristol stool index, IBS, and olfactory function were not significantly correlated with PD severity (Supplementary Fig. 4 and Supplementary Table 4).