OPN1MW and multiple system atrophy: To analyze the agreement levels of RT-QuIC and PMCA data for αSynP seeding activity in the cadavers who were examined by both assays, we conducted stratified analyses using Spearman rank correlations by each disease (PD [n = 24]: r = 0.44; P = .03; MSA [n = 3]: r = 0.50; P > .99; LBD [n = 5]: r = 0.90; P = .04; PSP [n = 5]: r = 0.80; P = .10; CBD [n = 5]: r = 0.80; P = .10) (eFigure 2 in the Supplement).