First-in-Human Study to Evaluate the Safety, Tolerability, Pharmacokinetics, and Pharmacodynamics of Single Ascending Doses of Intrathecally Administered ALN-SNCA in Participants With Early Parkinson's Disease
This study is researching an experimental drug called ALN-SNCA (called study drug). The study is focused on people with early Parkinson's disease, a disorder of the nervous system that affects movement. Parkinson's disease is caused by a gradual loss of nerve cells in the brain, especially those due to the harmful build-up of a protein called α-synuclein. The aim of the study is to see if the study drug is safe and tolerated well enough to continue testing it in future studies and what side effects may happen from taking the study drug. The study is looking at several other research questions, including: * Whether the study drug can lower the level of α-synuclein protein in the Cerebrospinal Fluid (also referred to as CSF, the fluid that surrounds the brain and spinal cord) * How much study drug is in the blood, urine, and CSF at different times * Compatible research to better understand the study drug (ALN-SNCA) and Parkinson's disease, including (but not limited to), whether the study drug can slow down the progression of Parkinson's disease symptoms
• Diagnosis of Parkinson's disease according to the Movement Disorder Society (MDS) criteria, as assessed by the investigator, with bradykinesia plus at least one of the other cardinal signs of Parkinson's disease (resting tremor, rigidity), without any other known or suspected cause of Parkinsonism
• A diagnosis of Parkinson's disease for 4 years or less at the screening visit
• Participant must meet one of the following criteria:
‣ Currently not receiving any standard-of-care (SoC) therapy for Parkinson's disease, has not been on oral dopaminergic therapy (ie, levodopa, dopamine agonists, or Monoamine Oxidase B \[MAO-B\] inhibitors) prior to dosing, and is not anticipated to require SoC therapy for Parkinson's disease within approximately 6 months following dosing, or
⁃ Has been on a stable regimen of oral dopaminergic therapy for at least 3 months prior to dosing and is not anticipated to require dose adjustments within approximately 6 months following dosing
• BMI ≤35 kg/m\^2 at time of screening visit