Although several different clinical trial designs have been employed,2–4 the most common and straightforward methodology to test a promising disease modifying therapy is to assess its ability to slow progression of clinical signs and symptoms versus placebo over time in patients with early PD while they are not receiving symptomatic PD medications (e.g., levodopa, dopamine agonists, MAO-B inhibitors). Here, MAOB is linked to Parkinson disease.