The drug being tested in this study is called TAK-341. The study will evaluate the efficacy, safety, tolerability, pharmacokinetics (PK), and pharmacodynamics of intravenous (IV) TAK-341 in participants with multiple system atrophy (MSA).~The study will enroll approximately 138 participants. The study comprises a screening period of up to 42 days (6 weeks), a 52-week double-blind treatment period, and a follow-up safety visit. Participants will be randomly assigned (by chance, like flipping a coin) to one of the treatment schedules-which will remain undisclosed to the participant, care provider and investigator during the study:~Early PK Cohort: TAK-341 Dose 1~Early PK Cohort: Placebo~Main Cohort: TAK-341 Dose 2~Main Cohort: Placebo~The change from baseline in UMSARS will be measured at Week 52 post-dose.~This multi-center trial will be conducted worldwide. The duration of treatment in this study will be 52 weeks. Participants will make a follow-up visit to the site after approximately 90 days after the last dose of study treatment. Early-termination participants will not make a follow-up safety visit.
The main aim is to see how TAK-341 works after 52 weeks in participants with multiple system atrophy as measured by the Unified Multiple System Atrophy Rating Scale Part I (UMSARS).~The study will enroll approximately 138 patients. Participants will receive a total of 13 intravenous infusions every 4 weeks approximately, these may be either of TAK-341 or placebo, after each infusion some blood samplings will be taken and other assessments completed.~This trial will be conducted in North America, Europe and Asia.