APOE ε4 influences the widespread TDP-43 pathological subtype in sporadic amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder, most sporadic cases exhibiting TAR DNA-binding protein 43 (TDP-43) pathology. The anatomical distribution of TDP-43 pathology varies among patients; however, factors contributing to this heterogeneity remain unclear. Apolipoprotein E (APOE) ε4 is known to influence the spread of pathological protein in several neurodegenerative diseases, raising the possibility that it also modulates the pathological distribution of TDP-43 inclusions in ALS. We investigated this hypothesis in a cohort of 145 autopsy-confirmed sporadic ALS cases. ALS-associated TDP-43 pathology was classified into two subtypes: type 1 - largely restricted to motor regions - and type 2 - characterized by widespread cortical involvement. APOE genotypes and rare variants in known ALS-associated genes were determined by exome sequencing. Amyloid-β and tau pathologies were assessed neuropathologically using established staging systems. Structural equation modeling (SEM) was applied to disentangle direct and indirect relationships among APOE ε4, temporal clinical parameters, Alzheimer's disease-related pathologies, and ALS TDP-43 subtype. Furthermore, we also performed an unbiased evaluation using random forest model. APOE ε4 carriers showed a significantly higher proportion of type 2 pathology than non-carriers. Bayesian SEM demonstrated that APOE ε4 was directly associated with the type 2, widespread TDP-43 subtype, independent of amyloid-β and tau pathology, while also reproducing the canonical cascade linking APOE ε4 to amyloid-β and tau. Rare variants in ALS-associated genes showed no clear effect on TDP-43 subtype. These findings indicate that APOE ε4 modifies the anatomical distribution of TDP-43 pathology in sporadic ALS through mechanisms independent of classical Alzheimer's disease pathology. Incorporation of APOE genotype into ALS stratification may be informative for biologically grounded subtype-specific therapeutic approaches.