Tofersen is an antisense oligonucleotide (ASO) developed by Biogen for the treatment of Amyotrophic Lateral Sclerosis (ALS) caused by mutations in the SOD1 gene. ASOs are short synthetic strands of nucleic acids that can selectively bind to target RNA molecules. In the case of Tofersen, it is designed to specifically bind to the messenger RNA (mRNA) produced by the SOD1 gene. By binding to the SOD1 mRNA, Tofersen helps prevent the production of the toxic SOD1 protein, which is believed to play a role in the degeneration of motor neurons. Tofersen is designed to bind to SOD1 mRNA and degrade SOD-1 mRNA, reducing SOD1 protein production.