AbstractBackgroundIdentification of a peripheral biomarker is a major roadblock in the diagnosis of PD. Immunohistological identification of p‐serine 129 α‐synuclein in the submandibular gland tissues of PD patients has been recently reported.ObjectiveWe report on a proof‐of‐principle study for using an ultra‐sensitive and specific, real‐time quaking‐induced conversion assay to detect pathological α‐synuclein in the submandibular gland tissues of PD patients.MethodsThe α‐synuclein real‐time quaking‐induced conversion assay was used to detect and quantify pathological α‐synuclein levels in PD, incidental Lewy body disease, and control submandibular gland tissues as well as in formalin‐fixed paraffin‐embedded sections.ResultsWe determined the quantitative seeding kinetics of pathological α‐synuclein present in submandibular gland tissues from autopsied subjects using the α‐synuclein real‐time quaking‐induced conversion assay. A total of 32 cases comprising 13 PD, 3 incidental Lewy body disease, and 16 controls showed 100% sensitivity and 94% specificity. Interestingly, both PD and incidental Lewy body disease tissues showed 100% concordance for elevated levels of pathological α‐synuclein seeding activity compared to control tissues. End‐point dilution kinetic analyses revealed that the submandibular gland had a wide dynamic range of pathological α‐synuclein seeding activity.ConclusionsOur results are the first to demonstrate the utility of using the real‐time quaking‐induced conversion assay on peripherally accessible submandibular gland tissues and formalin‐fixed paraffin‐embedded tissue sections to detect PD‐related pathological changes with high sensitivity and specificity. Additionally, the detection of seeding activity from incidental Lewy body disease cases containing immunohistochemically undetected pathological α‐synuclein demonstrates the α‐synuclein real‐time quaking‐induced conversion assay's potential utility for identifying prodromal PD in submandibular gland tissues. © 2019 International Parkinson and Movement Disorder Society