CAMBRIDGE, Mass. — Biogen Inc. (Nasdaq: BIIB) presented additional results from the Phase 1b study of salanersen, an investigational novel antisense oligonucleotide (ASO) given once a year for spinal muscular atrophy (SMA), at the 2026 Muscular Dystrophy Association (MDA) Clinical & Scientific Conference. The study evaluated salanersen in children who had suboptimal clinical status despite prior administration of gene therapy (onasemnogene abeparvovec-xioi). Salanersen was generally well-tolerated. Participants experienced a slowing of neurodegeneration and functional improvement, including achievement of new World Health Organization (WHO) motor milestones, following initiation of salanersen. These new results include a minimum of one year of follow-up for all participants, building on the interim study data presented at Cure SMA 2025. The company also presented the study designs of the Phase 3 salanersen clinical trials.
“Spinal muscular atrophy has benefitted from extraordinary therapeutic progress, but across the treatment landscape there remains room for improvement. There is growing scientific and clinical enthusiasm about the advances that salanersen offers,” said Thomas Crawford, M.D., co-director, Muscular Dystrophy Association Clinic at Johns Hopkins Medicine. “These additional Phase 1 data add confidence in the emerging salanersen clinical profile. We have more reason to look forward to results of the Phase 3 program.”
Salanersen Phase 1b Study Results
In this analysis, new data are available for study participants (n=24, aged 0.5-12 years), all of whom have received at least 2 doses of salanersen (40 mg or 80 mg). The 80 mg dose will be further evaluated in the Phase 3 studies.
In participants who received salanersen 40 mg and 80 mg and had elevated baseline concentrations of neurofilament light chain (NfL), a marker of ongoing neurodegeneration, meaningful reductions (75%) in NfL levels were observed at six months; these reductions were sustained throughout the follow-up period. All 24 participants treated with salanersen experienced improvement from baseline on one or more endpoints. Notably, 12 of the 24 achieved at least one new WHO motor milestone, and all participants maintained the motor milestones documented at their baseline. Salanersen has been generally well-tolerated at both 40 and 80 mg doses in the ongoing Phase 1 study, and most adverse events (AEs) have been mild to moderate in severity. As of the analysis, the most common AEs in the 40 mg group were upper respiratory tract infection and vomiting, and the most common AEs in the 80 mg group were pyrexia and upper respiratory tract infection.
Salanersen Phase 3 Clinical Development Program
Biogen also presented the design of the Phase 3 clinical program that will evaluate once-yearly salanersen 80 mg across the broad SMA population. The program is comprised of three global studies:
- STELLAR-1, an open-label study, will evaluate the effects of salanersen in young (under 6 weeks old), treatment-naïve and clinically presymptomatic infants with a genetic diagnosis of SMA.
- STELLAR-2, a randomized, double-blind, sham-controlled study, will evaluate the effects of salanersen when initiated ~6 months after onasemnogene abeparvovec-xioi in infants with SMA who received presymptomatic treatment with the gene therapy at 6 weeks of age or younger.
- SOLAR, an open-label study, will evaluate the effects of salanersen in teens and older adults (aged 15–60 years) with SMA who are either treatment-naïve or previously treated with risdiplam.
The STELLAR trials are complementary and designed to compare multiple early treatment strategies in presymptomatic newborns – salanersen alone, gene therapy alone, and salanersen as an add-on to gene therapy – to inform future treatment approaches in SMA. The clinical development program has already commenced with STELLAR-1 initiated screening, and the other studies planned to initiate in Q2 2026 (SOLAR) and Q3 2026 (STELLAR-2).
“With the encouraging Phase 1b results in hand, we are initiating the Phase 3 STELLAR-1, STELLAR-2, and SOLAR salanersen studies as quickly as possible,” said Stephanie Fradette, Pharm.D., Head of the Neuromuscular Development Unit at Biogen. “Together with the SMA community, we have designed these studies to confidently answer the most relevant questions for the field and establish salanersen’s role in the future treatment landscape.”
In addition to being presented at MDA, these data will also be shared at the 5th International Scientific Congress on SMA (SMA Europe 2026).
About Salanersen
Salanersen (BIIB115) is a novel, intrathecally administered antisense oligonucleotide (ASO) in development for SMA. Salanersen is designed to correct splicing of SMN2 pre-mRNA to increase production of SMN protein. It has a new backbone chemistry that leads to high potency, enabling the potential for high efficacy with once-yearly dosing.
Salanersen is being evaluated in three global Phase 3 studies designed to evaluate safety and efficacy of 80 mg administered once-yearly in a broad spectrum of individuals living with SMA. Biogen licensed the global development, manufacturing and commercialization rights for salanersen from Ionis Pharmaceuticals, Inc. Salanersen was discovered by Ionis.
About Spinal Muscular Atrophy (SMA)
SMA is a rare, genetic, neuromuscular disease that affects individuals of all ages. It is characterized by a loss of motor neurons in the spinal cord and lower brain stem, resulting in progressive muscle atrophy and weakness.1 SMA is caused by a deficiency in the production of survival motor neuron (SMN) protein due to a damaged or missing SMN1 gene, with a spectrum of disease severity.1 Some individuals with SMA may never sit; some sit but never walk; and some walk but may lose that ability over time.2 In the absence of treatment, children with the most severe form of SMA would usually not be expected to reach their second birthday.1
SMA impacts approximately 1 in 10,000 live births,3-6 is a leading cause of genetic death among infants7 and causes a range of disability in teenagers and adults.2
About Biogen
Founded in 1978, Biogen is a leading biotechnology company that pioneers innovative science to deliver new medicines to transform patients’ lives and to create value for shareholders and our communities. We apply deep understanding of human biology and leverage different modalities to advance first-in-class treatments or therapies that deliver superior outcomes. Our approach is to take bold risks, balanced with return on investment to deliver long-term growth. We routinely post information that may be important to investors on our website at www.biogen.com. Follow us on social media – Facebook, Instagram, LinkedIn, X, YouTube.
References
- National Institute of Neurological Disorders and Stroke, NIH. Spinal Muscular Atrophy Fact Sheet. Available at https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Fact-Sheets/Spinal-Muscular-Atrophy-Fact-Sheet. Accessed: March 2026.
- Wadman RI, Wijngaarde CA, Stam M, et al. Muscle strength and motor function throughout life in a cross-sectional cohort of 180 patients with spinal muscular atrophy types 1c–4. Eur J Neurol. 2018;25(3):512-518.
- Arkblad E, Tulinius M, Kroksmark AK, Henricsson M, Darin N. A population-based study of genotypic and phenotypic variability in children with spinal muscular atrophy. Acta Paediatr. 2009 May;98(5):865-72. doi: 10.1111/j.1651-2227.2008.01201.x. Epub 2009 Jan 20.
- Jedrzejowska M, Milewski M, Zimowski J, Zagozdzon P, Kostera-Pruszczyk A, Borkowska J, Sielska D, Jurek M, Hausmanowa-Petrusewicz I. Incidence of spinal muscular atrophy in Poland–more frequent than predicted? Neuroepidemiology. 2010;34(3):152-7. doi: 10.1159/000275492. Epub 2010 Jan 15.
- Prior TW, Snyder PJ, Rink BD, Pearl DK, Pyatt RE, Mihal DC, Conlan T, Schmalz B, Montgomery L, Ziegler K, Noonan C, Hashimoto S, Garner S. Newborn and carrier screening for spinal muscular atrophy. Am J Med Genet A. 2010 Jul;152A(7):1608-16. doi: 10.1002/ajmg.a.33474.
- Sugarman EA, Nagan N, Zhu H, Akmaev VR, Zhou Z, Rohlfs EM, Flynn K, Hendrickson BC, Scholl T, Sirko-Osadsa DA, Allitto BA. Pan-ethnic carrier screening and prenatal diagnosis for spinal muscular atrophy: clinical laboratory analysis of >72,400 specimens. Eur J Hum Genet. 2012 Jan;20(1):27-32. doi: 10.1038/ejhg.2011.134. Epub 2011 Aug 3.
- Kolb SJ, Coffey CS, Yankey JW, et al. Natural history of infantile-onset spinal muscular atrophy. Ann Neurol. 2017;82(6):883-891. doi:10.1002/ana.25101.
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