This clinical trial is focused on studying Amyotrophic Lateral Sclerosis (ALS), a progressive disease that affects nerve cells in the brain and spinal cord, leading to muscle weakness and loss of muscle control. The study will evaluate a treatment called ARGX-119, which is a humanized IgG1 monoclonal antibody designed to target a specific protein involved in muscle function. This treatment is administered as a concentrate for solution for infusion, meaning it is given through a vein.

The purpose of the study is to assess the safety and tolerability of ARGX-119 in people with ALS. Participants will be randomly assigned to receive either the treatment or a placebo, which is a substance with no active medication. The study will be conducted in a double-blinded manner, meaning neither the participants nor the researchers will know who is receiving the actual treatment or the placebo. This helps ensure the results are unbiased. The study will also include an active-treatment extension phase, allowing researchers to gather more information about the treatment’s effects over time.

Throughout the study, participants will undergo various assessments to monitor their health and the effects of the treatment. These assessments will include checking for any adverse events, conducting clinical laboratory tests, and measuring vital signs. The study will also look at how the body processes ARGX-119 and whether the immune system produces any antibodies against it. The trial is expected to continue until 2027, providing valuable insights into the potential benefits and safety of ARGX-119 for individuals with ALS.