Skip to content
You are now leaving to visit


Ulefnersen, formerly known as ION363, is an investigational antisense medicine designed to reduce the production of the fused in sarcoma (FUS) protein to treat people with amyotrophic lateral sclerosis (ALS) caused by mutations in the FUS gene. Ulefnersen is also known as Jacifusen (not an official USAN name) in honor of Jaci Hermsted, the first patient treated with the drug under an expanded access program. Because antisense-mediated reduction of mutant FUS protein in a FUS-ALS mouse model demonstrated the ability to prevent motor neuron loss, it is hypothesized that reduction of FUS protein will reverse or prevent disease progression in FUS-ALS patients. 


FUS-ALS is a rare, fatal, neurodegenerative disorder characterized by muscle weakness, loss of movement, and difficulty breathing and swallowing, resulting in a severely declining quality of life and eventually death. Current treatment options are extremely limited, with no medicines that significantly slow disease progression. It is estimated that there are approximately 350 patients with FUS-ALS in G7 countries.

Safety and efficacy have not been evaluated by any regulatory authorities for the indications described.