For my wife who has PD for about 16 years, cognition and psychosis is more of a problem than moving.
Plasma α-synuclein predicts cognitive decline in Parkinson's disease. - PubMed - NCBI
CONCLUSIONS:
Our data suggest that plasma α-synuclein level correlates with cognitive decline but not motor severity in patients with PD. Plasma α-synuclein could serve as a surrogate biomarker for patients at risk of cognitive decline.