30-07-2025
MHRA Approves First Targeted Drug for SOD1-ALS
The Medicines and Healthcare products Regulatory Agency (MHRA) has approved tofersen (Qalsody, Biogen) for treating amyotrophic lateral sclerosis (ALS) in adults with mutations in the superoxide dismutase 1 (SOD1) gene, also known as SOD1-ALS.
The approval makes tofersen the first targeted therapy in the UK against this rare form of motor neurone disease (MND) with a genetic basis.
A Rare but Aggressive Condition
SOD1-ALS causes the body to produce a misfolded, toxic version of the SOD1 protein. This triggers motor neuron degeneration in the brain and spinal cord.
Patients experience progressive muscle weakness, atrophy, respiratory decline, and eventual paralysis and death.
SOD1 mutations are responsible for approximately 2% of all ALS cases globally. Over 200 distinct mutations in SOD1 have been identified, each contributing to a wide range of disease progression rates. This variability highlights the importance of developing targeted therapies for SOD1-ALS.
How Tofersen Works
Tofersen is an antisense oligonucleotide that binds to SOD1 mRNA, promoting its degradation through an RNase H-mediated mechanism. This reduces the production of the toxic SOD1 protein.
The drug is administered via intrathecal injection through a lumbar puncture at scheduled intervals, under the supervision of trained healthcare professionals.
Success in Clinical Trials
The approval was supported by data from the phase 3 VALOR study and its open-label extension (OLE).
In the VALOR trial, 108 adults with SOD1-ALS were treated with either intrathecal tofersen (n=72) or placebo (n=36) for 28 weeks.
The primary endpoint, the ALSFRS-R score — which assesses bulbar, motor, and respiratory functions — showed a positive trend with tofersen, although the difference was not significant. However, tofersen significantly reduced biomarkers of neurodegeneration, including cerebrospinal fluid (CSF) SOD1 protein levels and plasma neurofilament light chain (NfL) concentrations. By week 28, plasma NfL levels decreased by 55% in the tofersen group, compared to a 12% increase with placebo.
Clinical trends suggested improvements in respiratory function, muscle strength, and quality of life. These effects were more pronounced with earlier treatment and during the OLE phase.
Safety and Tolerability
The most common side effects in tofersen-treated patients included:
Back, muscle, and joint pain
Fatigue
Fever
Raised CSF protein levels or white blood cell counts
These reactions were generally mild to moderate in severity.
Further information, including the Patient Information Leaflet and Summary of Product Characteristics, will be available on the MHRA website within 7 days of approval.