What to Test in Parkinson Disease Prevention Trials? Repurposed, Low-Risk, and Gene-Targeted Drugs.

Despite the sound epidemiologic and basic science rationales underpinning numerous "disease modification" trials in manifest Parkinson disease (PD), none has convincingly demonstrated that a treatment slows progression. Rapidly expanding knowledge of the genetic determinants and prodromal features of PD now allows realistic planning of prevention trials with initiation of putatively neuroprotective therapies earlier in the disease. In this article, we outline the principles of drug selection for PD prevention trials, focused on proof-of-concept opportunities that will help establish a methodological foundation for this fledgling field. We describe prototypical, relatively low-risk drug candidates for such trials (e.g., albuterol, ambroxol, caffeine, ibuprofen), tailored to specific at-risk populations ranging from pathogenic or gene variant carriers to those defined by prodromal PD and α-synucleinopathy. Finally, we review gene-targeted approaches currently in development targeting clinically manifest PD for their potential in future prevention trials.