Twelve of 24 children with spinal muscular atrophy achieved new motor milestones in a clinical trial. Abilities like unsupported sitting or independent walking that were previously impossible. Researchers from the Universities of Oulu, Helsinki, and Turku documented this behaviour on June 4 in the journal Science. It is the first confirmed example of spontaneous problem-solving in an invertebrate.
What Is Spinal Muscular Atrophy?
Spinal muscular atrophy, or SMA, is a hereditary disease of the nervous system. The protein SMN, which keeps motor neurons in the spinal cord alive, is not produced in sufficient quantity in affected children. The severest form, SMA Type 1, once almost always led to death before age two, accompanied by progressive muscle loss and respiratory failure. SMA affects about one in 10,000 newborns.
Since 2016, treatment has fundamentally changed. Nusinersen (brand name Spinraza), the first SMA drug ever, won FDA approval that year and significantly extended survival for Type 1 children. In 2019 came onasemnogene abeparvovec (Zolgensma), a one-time gene therapy that directly delivers the missing SMN1 gene into cells. With an introductory price of 2.1 million US dollars, it was then the world's most expensive medicine. Today, many children with SMA Type 1 survive infancy and school age. Some walk on their own legs.
Why Salanersen Now?
Gene therapies like Zolgensma don't work equally well in all patients. Some children respond suboptimally or stop benefiting from treatments after initial gains. Salanersen targets exactly here. The drug is an antisense oligonucleotide: a short synthetic molecule that directly intervenes in the splicing process of the SMN2 gene, increasing production of the missing protein. The principle resembles Nusinersen, but the chemistry is so advanced that Salanersen requires only one annual injection into the spinal fluid, unlike Nusinersen's multiple yearly doses.
According to Biogen's June 4 statement, all 24 Phase 1b participants showed improvements in at least one endpoint. In 12 of 24 children, new WHO motor milestones were documented: children who had never sat unsupported learned to do so. Some took first steps. Additionally, neurofilament light-chain levels, a biomarker for nerve cell death, fell measurably after six months and remained stable.
In Comparison: How SMA Treatment Redefines the Possible
Salanersen joins two other moments showing how the prognosis of a fatal inherited disorder can reverse within years. Nusinersen in 2016 was the first time any SMA drug worked clinically. A child who would have needed ventilation could reach school age thanks to treatment. Zolgensma in 2019 then showed a single therapy could permanently address the genetic cause.
The FDA Breakthrough Therapy Designation provides context: since its introduction in 2012, only 374 drugs received this status through end of 2025. It's reserved for disorders where preliminary data suggest substantial advantage over existing therapies. In the SMA space, it was last awarded to Zolgensma.
What Three Phase-3 Trials Must Show
Biogen launches three Phase 3 clinical trials in 2026. STELLAR-1 is already recruiting and tests Salanersen in newborns whose SMA was detected by genetic screening before symptoms appear. STELLAR-2, planned for June 2026, targets toddlers six months after prior gene therapy. SOLAR, also slated for Q2 2026, tests Salanersen in adolescents and adults aged 15 to 60 who are either untreated or have received Risdiplam.
Three conditions must be met for these trials to lead to approval. First, primary endpoints—unsupported sitting at twelve months and independent walking at eighteen months—must be statistically significantly better than in untreated historical controls or active comparison therapies. Second, the safety profile must justify intrathecal administration, even with repeated annual doses. Third, the question of compatibility with Zolgensma must be clinically answered. STELLAR-2 targets exactly this patient group, who had few options until now. Only when all three conditions are met does breakthrough status become an approved drug.