SOD1
SOD1 was one of the first genes identified as a cause of ALS, marking a turning point in understanding neurodegeneration as, in some cases, a genetically driven process rather than purely sporadic disease. It accounts for a meaningful subset of familial ALS cases and has been studied extensively, making it one of the best-characterized disease genes in neurology. Unlike some other ALS-associated genes, SOD1 mutations are not typically linked to frontotemporal dementia (FTD), which helps define it as a more motor neuron–specific subtype within the ALS spectrum.
Normal function
SOD1 encodes superoxide dismutase 1, an enzyme that is critical for cellular antioxidant defense by converting superoxide radicals into less harmful compounds. This reaction is critical because superoxide is highly reactive and can damage proteins, lipids, and DNA. SOD1 is found in multiple cellular compartments, including the cytosol and mitochondrial intermembrane space, making it a frontline defense against oxidative stress generated during normal metabolism.
Mutation and effect
Most disease-associated SOD1 mutations do not simply reduce enzyme activity. Instead, they cause the protein to adopt abnormal conformations, leading to misfolding and aggregation. These mutant forms gain toxic properties that interfere with multiple cellular systems. Importantly, even mutations that retain enzymatic activity can still cause disease, reinforcing that toxicity arises from altered protein behavior rather than simple loss of antioxidant function.
Overall, mutant SOD1 drives disease through a combination of protein misfolding, changes in interactions with cellular components, and disruption of intracellular transport systems. It can accumulate on mitochondria, impairing their function, and interfere with axonal transport, which is essential for maintaining motor neurons that can be up to 3 feet long. These mechanisms converge to selectively stress motor neurons, which are especially vulnerable due to their size, metabolic demand, and reliance on long-distance transport.
Implications for treatment
SOD1-associated ALS often shows less involvement of TDP-43 mislocalization and aggregation, which is otherwise a hallmark of most ALS cases. Instead, pathology is more directly linked to SOD1 protein accumulation and toxicity. Clinically, disease course can vary widely depending on the specific mutation, with some variants causing rapid progression and others leading to slower disease trajectories.
SOD1 has become a proof-of-concept target for gene-directed therapy, particularly through antisense oligonucleotides designed to reduce SOD1 expression. This approach represents one of the clearest demonstrations that directly targeting a causative gene can alter disease biology, even if long-term clinical outcomes are still being defined.
Research focus
Current research is centered on refining gene-silencing approaches, identifying biomarkers of treatment response, and understanding how mutant SOD1 exerts toxicity across different cellular compartments. Lessons learned from SOD1 are also being applied to other ALS genes and broader neurodegenerative diseases.
Sources
- Bunton-Stasyshyn, R. K. A., Saccon, R. A., Fratta, P., & Fisher, E. M. C. (2015). SOD1 Function and Its Implications for Amyotrophic Lateral Sclerosis Pathology: New and Renascent Themes.
- Benatar, M., Wuu, J., Andersen, P. M., et al. (2025). Amyotrophic lateral sclerosis caused by SOD1 variants.
- Tsekrekou, M., et al. (2024). Protein aggregation and therapeutic strategies in SOD1-ALS.
- Miller, T. M., Cudkowicz, M. E., Genge, A., et al. (2022). Trial of Antisense Oligonucleotide Tofersen for SOD1 ALS.