Tofersen is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.
Tofersen (brand name: QALSODY) is an intrathecally administered [antisense oligonucleotide
(ASO)[/treatments/[antisense-oligonucleotide-therapy[/treatments/[antisense-oligonucleotide-therapy[/treatments/[antisense-oligonucleotide-therapy--TEMP--/treatments)--FIX-- designed to treat [amyotrophic lateral sclerosis (ALS)[/diseases/[als[/diseases/[als[/diseases/[als--TEMP--/diseases)--FIX-- caused by mutations in the
[superoxide dismutase 1 (SOD1) gene. On April 25, 2023, the FDA granted accelerated approval to tofersen, making it the first therapy to
target a genetic cause of ALS [[1]https://investors.biogen.com/news-releases/news-release-details/fda-grants-accelerated-approval-qalsodytm-tofersen-SOD1-als)
[[2]https://ir.ionis.com/news-releases/news-release-details/fda-approves-qalsodytm-tofersen-first-treatment-targeting).
Developed jointly by Biogen and Ionis Pharmaceuticals, tofersen represents a paradigm shift in ALS therapeutics—from symptom management to
precision medicine targeting the underlying genetic cause of disease.
SOD1 mutations account for approximately 2% of all ALS cases and roughly 12–20% of familial ALS cases. These mutations lead to the
production of misfolded, toxic SOD1 protein that accumulates in [motor [neurons[/entities/[neurons[/entities/[neurons[/entities/[neurons--TEMP--/entities)--FIX--, contributing to neurodegeneration through [oxidative
stress[/mechanisms/[oxidative-stress[/mechanisms/[oxidative-stress[/mechanisms/[oxidative-stress--TEMP--/mechanisms)--FIX--, [mitochondrial dysfunction[/mechanisms/[mitochondrial-dysfunction[/mechanisms/[mitochondrial-dysfunction[/mechanisms/[mitochondrial-dysfunction--TEMP--/mechanisms)--FIX--, and [protein aggregation[/mechanisms/[protein-aggregation[/mechanisms/[protein-aggregation[/mechanisms/[protein-aggregation--TEMP--/mechanisms)--FIX-- [[3]]]https://investors.biogen.com/news-releases/news-release-details/fda-grants-accelerated-approval-qalsodytm-tofersen-SOD1-als)
[Neurofilament light chain (NfL)[/proteins/[nfl-protein[/proteins/[nfl-protein[/proteins/[nfl-protein--TEMP--/proteins)--FIX-- is a structural protein released from damaged axons into cerebrospinal fluid and blood. Elevated plasma
[NfL[/entities/[neurofilament-light[/entities/[neurofilament-light[/entities/[neurofilament-light--TEMP--/entities)--FIX-- concentrations are a sensitive indicator of active neurodegeneration and have emerged as a key biomarker in ALS. Tofersen's
accelerated approval was based on its ability to significantly reduce plasma [NfL[/entities/[neurofilament-light[/entities/[neurofilament-light[/entities/[neurofilament-light--TEMP--/entities)--FIX-- levels, which served as a surrogate biomarker reasonably
likely to predict clinical benefit [[1]https://investors.biogen.com/news-releases/news-release-details/fda-grants-accelerated-approval-qalsodytm-tofersen-SOD1-als)
[[3]]]https://investors.biogen.com/news-releases/news-release-details/fda-grants-accelerated-approval-qalsodytm-tofersen-SOD1-als)
[5]
The initial Phase 1–2 ascending-dose trial enrolled 50 adults with SOD1-ALS and evaluated tofersen at doses of 20 mg, 40 mg, 60 mg, and 100 mg. The study demonstrated dose-dependent reductions in CSF SOD1 protein concentrations and was generally well tolerated. The 100 mg dose achieved the greatest SOD1 reduction and was selected for the Phase 3 trial [[4]]]https://source.washu.edu/2025/12/new-als-drug-stabilizes-decline-with-a-trend-toward-improved-strength-mobility-for-some/)
A case series from Iceland documented that treatment with tofersen resulted in nonprogressive chronic ALS in some patients, with stabilization of ALSFRS-R scores over extended follow-up periods. These real-world observations provide additional support for tofersen's disease-modifying potential in SOD1-ALS [[8]https://link.springer.com/article/10.1007/s00415-025-13579-y).
The ATLAS study (NCT04856982) is a groundbreaking Phase 3, randomized, placebo-controlled trial evaluating tofersen in presymptomatic
carriers of SOD1 mutations—individuals who carry a disease-causing mutation but have not yet developed clinical symptoms. The trial targets
carriers of SOD1 variants associated with high or complete penetrance and rapid disease progression who show biomarker evidence of disease
activity (elevated plasma NfL) [[9])]https://pubmed.ncbi.nlm.nih.gov/35585374/).
Key details:
The ATLAS trial represents a bold test of whether presymptomatic intervention can delay or prevent clinical onset of ALS, which would have profound implications for genetic counseling, newborn screening, and the broader neurodegenerative disease field [[9])]https://pubmed.ncbi.nlm.nih.gov/35585374/).
The most common adverse effects of tofersen include:
Tofersen represents several important advances in neurodegenerative disease treatment:
Research is also exploring ASO approaches targeting other ALS genes, including [C9orf72[/genes/[c9orf72[/genes/[c9orf72[/genes/[c9orf72--TEMP--/genes)--FIX--, [FUS[/entities/[fus[/entities/[fus[/entities/[fus--TEMP--/entities)--FIX--, and [ATXN2[/genes/[atxn2[/genes/[atxn2[/genes/[atxn2--TEMP--/genes)--FIX--, which could extend the precision medicine approach to a larger proportion of ALS patients.
The study of Tofersen has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.
Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.