Since p-α-syn is considered as the marker of choice to delineate pathological aggregates from physiological α-syn deposits, we aimed to further refine the assessment of p-α-syn in the ENS by morphometric quantification of phospho-serin129-α-synuclein (p-S129-α-syn) positive aggregates both in neuronal somata and nerve fibers in rectal biopsies of patients with PD and controls. Here, SNCA is linked to Parkinson disease.