For comparative purposes, we also tested PD (n = 9) and HC (n = 1) IM biopsies for the presence of proteopathic seeds of another cytosolic protein, tau, using a tau RT-QuIC assay that ultrasensitively detects the tau seeds associated with either 3R (Pick’s disease) or 3R+4R (Alzheimer’s disease and chronic traumatic encephalopathy) tauopathies [35]. Here, MAPT is linked to Parkinson disease.