This study is for adults who are carriers of a gene change called *Superoxide Dismutase 1 (SOD1)* mutation, which can lead to ALS, a disease that affects nerves and muscles. The study tests a medicine called *tofersen* to see if it works and is safe when given before symptoms of ALS start. It checks if starting tofersen early helps control the disease better compared to starting it when symptoms appear.

• **Study Length:** Participants will need to be part of the study for a period determined by the research team.
• **Visits:** Regular visits to the study site are required to monitor health and effects of the medicine.
• **Risks:** Participants should be aware of potential side effects and need to discuss them with the study team.

To join, one must not show ALS symptoms and have no history of HIV, Hepatitis B, or C. Also, they must not have certain other health conditions or take specific medications. The study excludes those with certain medical histories or who are on certain drugs. Participants should discuss with their doctor if they meet the criteria and if the study is suitable for them.