FUS
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FUS is a gene associated with familial ALS, particularly in cases with early onset and aggressive progression. It belongs to a broader group of RNA-binding proteins that have emerged as central players in ALS biology, highlighting RNA regulation as a key vulnerability in motor neurons.
Normal function
FUS encodes a multifunctional RNA-binding protein that operates primarily in the nucleus, where it participates in RNA splicing, transport, and transcriptional regulation. It also contributes to DNA damage repair. Through these roles, FUS helps maintain proper gene expression and cellular integrity, particularly in neurons with high transcriptional and metabolic demands.
Mutation and effect
Disease-associated mutations often disrupt signals telling FUS to move to the nucleus, causing it to accumulate in the cytoplasm instead. This results in a dual problem: loss of normal nuclear function where, because of the lack of RNA processing, proteins are made incorrectly, and gain of toxic properties in the cytoplasm where FUS can form aggregates.
FUS pathology is driven by RNA dysregulation (when the normal control over how RNA molecules are processed and used breaks down), abnormal phase separation (a process where certain proteins and RNA molecules clump together into liquid-like droplets inside the cell, similar to how oil separates from water, which cells use to organize their contents but which can go wrong and form permanent clumps), and stress granule dysfunction (problems with stress granules, which are temporary clusters of RNA and protein that cells form during stressful conditions to pause non-essential activity, and which are meant to dissolve once the stress passes). In the cytoplasm, mutant FUS can become trapped in stress granules (temporary RNA-protein assemblies that form during cellular stress), altering their dynamics and persistence. This disrupts RNA processing and protein synthesis, contributing to cellular stress and impaired neuronal function.
Implications for treatment
FUS-associated ALS tends to present at a younger age and progress more rapidly than typical ALS. It often lacks classic TDP-43 pathology, indicating a distinct molecular subtype of disease driven by RNA-binding protein dysfunction rather than the more common TDP-43 pathway.
Therapeutic strategies aim to restore proper RNA regulation, prevent cytoplasmic aggregation, or correct protein localization, but these approaches are still largely experimental. The challenge is targeting toxic effects without disrupting the essential normal functions of FUS.
Research focus
Research on FUS is focused on how RNA-binding proteins become toxic when they mislocalize from the nucleus to the cytoplasm. A central question is how FUS mutations disrupt nuclear import, promote cytoplasmic aggregation, and alter the behavior of stress granules. Researchers are also exploring whether therapies can restore nuclear localization, reduce aggregation-prone FUS, or correct downstream RNA-processing defects. Because FUS-associated ALS is often early-onset and aggressive, there is strong interest in developing faster and more targeted therapeutic strategies.
Inheritance
FUS is a less common ALS gene, responsible for about 4-6% of familial cases and under 2% of cases with no family history. Most changes are dominant (only one mutated copy needed for disease), so if one parent is a carrier there is a 50/50 chance of the child inheriting a copy of the mutation. FUS stands out as the top cause of the rare juvenile form of ALS (starting before age 25), and in many of those young cases, the gene change appeared brand-new in that person rather than being inherited at all. Even so, carrying a FUS change is far from a guarantee of getting sick, as only around 19% of those carrying the gene will develop ALS, the lowest of the four major ALS genes.
Sources
- Moens, T. G., et al. (2025). Amyotrophic lateral sclerosis caused by FUS mutations.
- Xiao, X., et al. (2024). FUS gene mutation in amyotrophic lateral sclerosis.
- Mariani, D., et al. (2024). ALS-associated FUS mutation reshapes the RNA and protein composition of cytoplasmic ribonucleoprotein granules.
- Assoni, A. F., et al. (2023). Amyotrophic Lateral Sclerosis, FUS and Protein Synthesis Dysfunction.