Biogen’s Spinraza follow-up helps children with SMA who didn’t benefit from Zolgensma
Biogen has cited early results from a small phase 1 trial as evidence that its antisense oligonucleotide salanersen could help children with spinal muscular atrophy (SMA) who are still struggling to sit independently despite having received Novartis’ Zolgensma.
The phase 1 study was split into two parts: a healthy adult volunteer cohort and 24 children aged five months to 12 years with SMA who had previously received the gene therapy Zolgensma and were administered either 40 mg or 80 mg salanersen once a year. Biogen conducted an interim analysis of data from the latter cohort to help decide whether to take salanersen forward into registrational studies.
Of the children in the second part of the trial who had elevated baseline concentrations of neurofilament light chain (NfL)—a biomarker of neurodegeneration—salanersen was tied to a mean reduction in NfL of 70% at six months. This reduction was sustained for a year, Biogen explained in a press release on June 25th 2025.
Further interim data analysis identified eight patients aged between two and 12 years who received 40 mg of salanersen and had at least a one-year follow-up by the time of the analysis. Half of this subgroup achieved motor function milestones that they had previously not achieved despite receiving Zolgensma, according to Biogen. These included walking, crawling, standing or sitting.
“To see a child dosed with gene therapy at one year of age and still unable to sit without support at age five then gain the ability to sit independently just three months after initiating salanersen—that is unexpected,” said Valeria Sansone, M.D., Ph.D., Professor of Neurology at the University of Milan and a principal investigator for the trial.
Sansone noted that the data come from “a relatively small cohort,” and a larger trial is still needed to “further understand the effects that salanersen can have in both previously treated and treatment-naïve individuals.”
Assessing the safety data across the treated children, Biogen concluded that salanersen had a “generally well-tolerated safety profile” at both the 40 mg and 80 mg doses. Most adverse events were mild to moderate in severity, with no serious adverse events linked to the treatment itself. The most common side effects were fever (affecting 40% of patients) and upper respiratory tract infection (affecting 29%).
Salanersen, which was licensed from Ionis Pharmaceuticals, has the same mechanism of action as Biogen’s approved SMA antisense oligonucleotide therapy Spinraza but the pharma is aiming for greater potency and once-yearly dosing.
