First in Human (FIH) Study of ALN-SOD in Adult Participants With Amyotrophic Lateral Sclerosis Associated With Mutation in the SOD1 Gene (SOD1-ALS)

This study is researching an experimental drug called ALN-SOD (called "study drug"). This study is focused on people with Amyotrophic Lateral Sclerosis (ALS) caused by a change in a gene called the Superoxide Dismutase-1 (SOD1) gene. This type of ALS is known as "SOD1-ALS". This is the first time that ALN-SOD will be given to people. The aim of the study is to see how safe and tolerable the study drug is. The study is looking at several other research questions, including: * The effect the study drug has on specific biomarkers, which are substances in the blood or in the fluid that surrounds the brain and spinal cord, known as Cerebrospinal Fluid (CSF) * How much study drug is in the blood and in the CSF, at different times * Whether the body makes antibodies against the study drug (which could make the drug less effective or could lead to side effects) * What effects the study drug has on ALS symptoms