Biogen’s Salanersen Receives FDA Breakthrough Therapy Designation for Spinal Muscular Atrophy

A Major Step Forward for SMA Treatment

Biogen has announced that the U.S. Food and Drug Administration (FDA) has granted Breakthrough Therapy designation to salanersen, an investigational antisense oligonucleotide (ASO) therapy being developed for the treatment of spinal muscular atrophy (SMA).

The designation is an important milestone for Biogen and highlights the potential of salanersen to address ongoing treatment needs in people living with SMA. The therapy is designed to provide high efficacy with the convenience of once-yearly dosing, which could offer a significant advantage for patients and caregivers.

What Is Breakthrough Therapy Designation?

The FDA grants Breakthrough Therapy designation to medicines intended to treat serious conditions when early clinical evidence suggests they may provide substantial improvements over currently available treatments.

This designation helps speed up the development and review process, allowing promising therapies to reach patients more quickly if clinical results continue to be positive.

For salanersen, the FDA's decision reflects growing confidence in the treatment's potential based on early clinical findings.

Why New SMA Treatments Are Still Needed

Over the last several years, treatment options for spinal muscular atrophy have improved significantly. However, many patients continue to face challenges, and there remains a need for therapies that can provide additional benefits.

According to Dr. Diana Castro of the Neurology Rare Disease Center in Texas, the FDA's decision recognizes that there are still unmet needs within the SMA community and that further progress is possible.

She noted that children participating in the Phase 1b study showed unexpected improvements in important motor functions after receiving salanersen, even if they had previously received gene therapy.

Some patients gained abilities such as:

• Sitting independently

• Walking

• Improved overall motor function

These findings have generated considerable interest among clinicians and researchers working in SMA care.

Positive Results from the Phase 1b Study

The FDA's designation was supported by data from the ongoing Phase 1b clinical study of salanersen.

Results from the study were recently presented at major scientific meetings, including the 2026 Muscular Dystrophy Association Clinical & Scientific Conference and the 5th International Scientific Congress on SMA.

Researchers reported that children with SMA who had experienced a limited response to previous gene therapy showed clinically meaningful improvements after starting once-yearly salanersen treatment.

The study also showed:

• Improvements in motor function

• Slower neurodegeneration

• Reduced neurofilament levels, which are biomarkers associated with nerve damage

• A generally favorable safety and tolerability profile

These findings suggest that salanersen may provide benefits even for patients who have already received other SMA treatments.

How Salanersen Works

Salanersen is designed to increase the production of survival motor neuron (SMN) protein, which is essential for healthy muscle and nerve function.

The therapy works by correcting the splicing of SMN2 pre-mRNA, allowing the body to produce more functional SMN protein.

What makes salanersen different is its advanced chemistry, which increases its potency. This enhanced potency creates the possibility of achieving strong clinical effects with only one dose per year.

For many patients and families, reducing treatment frequency could help simplify long-term disease management.

Support from the SMA Community

The announcement has also been welcomed by patient advocacy groups.

Kenneth Hobby, President of Cure SMA, stated that the designation reflects both the FDA's commitment to the SMA community and the ongoing need for new treatment options.

He emphasized that many individuals living with SMA still face significant challenges and that promising therapies should be developed as quickly as possible.

The designation also aligns with feedback that the SMA community has recently provided to regulators regarding unmet treatment needs.

Biogen Advances Global Phase 3 Development Program

Biogen is now moving forward with a comprehensive Phase 3 clinical development program for salanersen.

The program includes three global studies designed to evaluate the therapy across different patient populations.

STELLAR-1

STELLAR-1 is currently recruiting participants.

The open-label study is evaluating salanersen in infants younger than six weeks of age who have been genetically diagnosed with SMA but have not yet developed symptoms or received treatment.

The goal is to determine whether very early intervention can improve long-term outcomes.

SOLAR

SOLAR is also actively recruiting participants.

This open-label study focuses on teenagers and adults aged 15 to 60 years living with SMA.

The trial includes both treatment-naïve patients and individuals who have previously received risdiplam.

STELLAR-2

Recruitment for STELLAR-2 is expected to begin in June 2026.

This randomized, double-blind, sham-controlled study will evaluate salanersen in infants who previously received gene therapy with onasemnogene abeparvovec-xioi during the presymptomatic stage of disease.

Researchers will study the impact of introducing salanersen approximately six months after gene therapy treatment.

A Potential Once-Yearly Treatment Option

One of the most exciting aspects of salanersen is its potential dosing schedule.

Unlike many therapies that require more frequent administration, salanersen is being developed as a once-yearly treatment.

All three Phase 3 studies are evaluating an 80 mg dose administered once per year.

If successful, this approach could provide a new level of convenience while maintaining strong clinical effectiveness.

Looking Ahead

The FDA's Breakthrough Therapy designation represents a significant achievement for Biogen and an encouraging development for the SMA community.

Early clinical data suggest that salanersen may offer meaningful improvements in motor function, slow neurodegeneration, and potentially address treatment gaps that still exist for many patients.

With multiple Phase 3 studies now underway, researchers will continue to evaluate the safety and effectiveness of this once-yearly therapy across a broad range of SMA patients.

As development progresses, salanersen could become an important addition to the future treatment landscape for spinal muscular atrophy, providing patients and families with another option in the fight against this serious genetic disease.