MUC2 and Parkinson disease: Specifically, the study investigated genetic polymorphisms in peptidoglycan recognition proteins PGLYRP2 and 4; toll-like receptors TLR1, 2 and 4 and co-receptor CD14; tight-junction claudins CLDN2 and 4; and mucin glycoproteins MUC1 and MUC2, to determine if they are associated with PD risk or age of symptom onset.