OCLN and Parkinson disease: Examination of morphological changes and expression in the intestinal epithelial barrier (including two tight junction proteins, ZO-1 and occludin) in colonic biopsy tissues of PD patients and controls showed that a greater proportion of PD patients had disrupted and irregularly distributed tight junction proteins and lower expression levels of occludin compared to controls (Clairembault et al., 2015) thus confirming observations of increased gut permeability and mild bowel inflammatory changes in patients with PD.