TDP43 M337V

The computational structure prediction for TDP-43 M337V was generated using AlphaFold2/ColabFold, achieving an average confidence score (pLDDT) of 65.8. This moderate confidence reflects the inherent difficulty of modeling the C-terminal domain where M337V resides—a region known for disorder and aggregation propensity. Regions with pLDDT below 70 represent areas of structural uncertainty where the predicted atomic positions should be interpreted cautiously. The mutation occurs at position 337, substituting methionine with valine in a critical C-terminal region that influences protein aggregation and cellular localization. Clinically, M337V is classified as pathogenic or likely pathogenic by multiple expert submitters in ClinVar with no conflicting interpretations, and importantly, this variant has never been observed in the gnomAD population database. This complete absence in healthy populations strongly supports its disease-causing role, as benign variants typically appear at low frequencies in the general population. The combination of expert pathogenicity classification and zero population frequency provides compelling evidence that M337V directly contributes to ALS and frontotemporal dementia pathogenesis. Research demonstrates that M337V drives neurodegeneration through multiple interconnected mechanisms that begin early in disease progression. The mutation impairs motor neuron viability, reduces neurite outgrowth, and slows axonal transport even without visible protein aggregation, indicating that cellular dysfunction precedes overt pathological hallmarks [1][5]. In patient-derived neurons, M337V increases both soluble and detergent-resistant TDP-43 levels, elevates motor neuron death risk substantially (hazard ratio 2.76), and creates vulnerability to disruptions in cellular survival signaling pathways [3]. Additionally, the mutation disrupts DNA damage responses through the Ku80-p53-SIRT1 axis, contributing to shared pathogenic mechanisms across both sporadic and familial ALS/FTD cases [3]. At the molecular level, M337V enhances protein aggregation propensity by affecting the C-terminal region's alpha-helical segment (residues 320-340), which normally regulates liquid-liquid phase separation—a process where proteins reversibly condense into droplets that can become pathological aggregates when dysregulated. The mutation alters stress granule dynamics (temporary RNA-protein assemblies formed during cellular stress), increases abnormal binding to other RNA-binding proteins, and impairs the protein's ability to bind and transport specific RNA molecules [4]. Genetic screens across multiple model organisms have identified modifiers of M337V toxicity in pathways controlling RNA metabolism, protein quality control, and cellular energy production, highlighting the broad cellular impact of this single amino acid change [1]. Animal models expressing M337V show reactive glial inflammation, abnormal protein ubiquitination, movement impairments, early lethality, and mitochondrial abnormalities [1]. Recent studies also reveal that M337V contributes to blood-brain barrier dysfunction through reduced nuclear TDP-43 in endothelial cells lining brain blood vessels, suggesting that this mutation affects not only neurons but also the vascular cells that support brain health [7]. Therapeutic research has identified that inhibiting glycogen synthase kinase-3 (GSK3) can suppress TDP-43-mediated toxicity through caspase-dependent mechanisms, and that compounds targeting multiple pathways simultaneously show promise in preventing motor neuron degeneration in experimental models [2][6]. These findings emphasize that while structural predictions like this AlphaFold model provide valuable hypotheses about mutation effects, the low-to-moderate confidence scores in the disordered C-terminal region limit direct structural interpretations without experimental validation.