In this study, researchers will learn more about the safety of tofersen, also known as Qalsody®. This is a drug available for doctors to prescribe for participant with a certain type of amyotrophic lateral sclerosis, also known as ALS. This type is in participant who have a mutation in the superoxide dismutase 1 gene, also known as SOD-1.

This is known as an "observational" study, which collects health information about study participants without changing their medical care. Participants for this study will be found using 2 different groups of study research centers that help provide clinical care for participant with ALS. These groups are in Europe and the United States and are called:

• the Precision-ALS programme
• the ALS/Motor Neuron Disease (MND) Natural History Consortium (NHC)

The main goal of this study is to collect safety information in participants with SOD-1 ALS who were in either of the groups.

The main question researchers want to answer in this study is:

• What are the characteristics of the participants in this study?
• How many participants had serious adverse events (SAEs), including ones that affect the brain, spinal cord, or nerves?

An adverse event is a health problem that may or may not be caused by a drug during the study. An adverse event is considered serious when it results in death, is life-threatening, causes lasting problems, or requires hospital care.

Researchers will also learn more about:

• How many participants develop other health conditions or become pregnant, including how the pregnancy turned out
• Why and when participants stopped treatment

This study will be done as follows:

• Participants will be screened to check if they can join the study.
• Data from the participants' regular visits to their clinic will be collected based on which study research center they are in.
• Each participant will be in the study until they decide to leave or until death. Currently, the study is planned to last at least 7 years.

The primary objectives of this study are to describe demographic and clinical characteristics of participants with superoxide dismutase 1-amyotropic lateral sclerosis (SOD1-ALS); to describe the frequency of SAEs among participants with SOD1-ALS, including serious neurologic events previously reported in clinical trial participants (e.g., myelitis, radiculitis, aseptic meningitis, increased intracranial pressure, and/or papilloedema).

The secondary objectives of this study are to describe the frequency of new comorbid conditions, pregnancy and pregnancy outcome among participants with SOD1-ALS; to describe the frequency of treatment discontinuation among participants with SOD1-ALS treated with tofersen.

NHC registry has started the data collection while the Treatment Research Initiative to Cure ALS (TRICALS) is yet to start.

Key Inclusion Criteria:

• Participants with an ALS diagnosis and a confirmed SOD1 mutation from contributing registry networks will be considered for inclusion in the study.

Key Exclusion Criteria:

• Data collected while a person with SOD1-ALS is participating in an interventional clinical trial (with tofersen or any other investigational medicinal product) will be excluded.

NOTE: Other protocol- defined Inclusion/Exclusion criteria may apply.

Participants with SOD1-ALS enrolled in TRICALS network's Precision-ALS programme with data from participating clinical centers across multiple European countries or at ALS/MND NHC with data from participating clinical centers in the United States (tofersen users and tofersen non-users).

In accordance with Biogen's Clinical Trial Transparency and Data Sharing Policy on https://www.biogentrialtransparency.com/