α-Synuclein has been proposed to be present in the colon mucosa in idiopathic Parkinson disease (IPD), reflecting the hypothesis that the disease begins in the gut. To assess the potential of α-synuclein in the colon mucosa as a biomarker for IPD, Antunes et al. performed immunohistochemical staining of colon mucosa biopsies from 19 patients with IPD and eight controls. The researchers reported that α-synuclein was present throughout the colon in both patients and healthy controls, indicating that conventional immunohistochemical staining of α-synuclein is not a useful biomarker for IPD.