Using data from the Parkinson's Progression Markers Initiative (PPMI) cohort, we aimed to test whether baseline α-syn seeding activity and α-syn SAA kinetic parameters are associated with disease progression in sporadic PD, LRRK2-associated PD (LRRK2 PD), and GBA-associated PD (GBA PD). Here, GBA1 is linked to Parkinson disease.