This study is intended to determine the efficacy and safety of the study drug AMX0035 in people living with Progressive Supranuclear Palsy (PSP). Participants will between the ages of 40 and 80 and will be randomized to receive AMX0035 or placebo. Study participation will last 52 weeks with 7 visits to the clinic. After study participation ends, there is the option for the participant to continue into the open-label extension period where they would receive AMX0035 for another 56 weeks.

This study is an open-label study that will evaluate SAGE-718 on the cognitive effects in subject with early manifest Huntington's Disease (HD). The subject will be on study drug for a year. At clinic visits, participants will take the IP under staff supervision, followed by assessments of cognitive function, health-related function and quality of life, and neuropsychiatric symptoms.

This study will test SAGE-718 to evaluate cognitive effects in subject with early manifest HD. The subject will be on study drug or placebo for 84 days. At clinic visits, participants will take the IP under staff supervision, followed
by assessments of cognitive function, health-related function and quality of life, and neuropsychiatric symptoms.