Biogen Inc. (NASDAQ: BIIB) reported additional Phase 1b clinical trial results for salanersen, an experimental treatment for spinal muscular atrophy, at the 2026 Muscular Dystrophy Association Clinical & Scientific Conference.

The study evaluated salanersen in 24 children aged 0.5-12 years who had received suboptimal results from prior gene therapy treatment. All participants received at least two doses of the drug at either 40 mg or 80 mg concentrations administered once yearly.

According to the company's statement, all 24 participants showed improvement on one or more clinical endpoints. Twelve participants achieved at least one new World Health Organization motor milestone, while all maintained their baseline motor functions. The treatment demonstrated a 75% reduction in neurofilament light chain levels, a marker of neurodegeneration, at six months in participants with elevated baseline concentrations.

The drug was generally well-tolerated at both dosage levels, with most adverse events classified as mild to moderate. Common side effects included upper respiratory tract infections, vomiting, and fever.

Biogen also announced the design of its Phase 3 clinical program, which will evaluate the 80 mg dose across three global studies. STELLAR-1 will test the treatment in presymptomatic infants under six weeks old. STELLAR-2 will examine salanersen as an add-on therapy approximately six months after gene therapy in infants. SOLAR will evaluate the drug in teenagers and adults aged 15-60 years.

Salanersen is an antisense oligonucleotide designed to increase production of survival motor neuron protein by correcting splicing of SMN2 pre-mRNA. Biogen licensed the development and commercialization rights from Ionis Pharmaceuticals.

The Phase 3 program has begun with STELLAR-1 screening initiated, while the other studies are planned to start in the second and third quarters of 2026.