TNF and irritable bowel syndrome: Likewise, various genetic (such as LRRK2 and TNF-α variants) [21, 22], environmental (e.g., pesticides) or lifestyle factors (diet, exercise, or antibiotic use) [23, 24] which mediate PD risk or progression, are also linked with intestinal inflammation and IBD, while IBD is itself known to be a risk factor for PD [25, 26].