Salanersen

In this study, researchers will learn about a study drug called BIIB115 in healthy male volunteers and in participants with spinal muscular atrophy (SMA). This study will focus on children with SMA.
The main objective of the study is to learn more about the safety of BIIB115 and how participants respond to different doses of BIIB115. The main question researchers want to answer is:
How many participants have adverse events and serious adverse events during the study? Adverse events are unwanted health problems that may or may not be caused by the study drug.
Researchers will also learn more about how the body processes BIIB115. They will do this by measuring the levels of BIIB115 in both the blood and the cerebrospinal fluid, also known as the CSF. This is the fluid around the brain and spinal cord.
The study will be split into 2 parts - Part A and Part B.
During Part A:
* After screening, healthy volunteers will be randomly placed into 1 of 4 groups to receive either BIIB115 or a placebo. A placebo looks like the study drug but contains no real medicine.
* Participants will receive a single dose of either BIIB115 or the placebo as an injection directly into the spinal canal on Day 1.
* Neither the researchers nor the participants will know if the participants will receive BIIB115 or the placebo.
* The treatment and follow up period will last for 13 months.
* Participants will have up to 6 clinic visits and 4 telephone calls.
During Part B:
* In Part B, children with SMA will receive BIIB115. Both researchers and participants will know they are receiving BIIB115.
* Participants will receive 2 total doses of BIIB115 given at 2 different times.
* The treatment and follow up period will last for 25 months.
* Participants will have up to 14 clinic visits and 6 telephone calls.
In both parts, participants will stay in the clinic for 24 hours after each dose for so that researchers can check on their health and any medical problems they might have.