APOE4 -specific glymphatic effects on clinical progression in the Alzheimer's Disease Neuroimaging Initiative with pathological correlates in the A4 study

Background The APOE ε4 allele is the strongest genetic risk factor for late-onset Alzheimer's disease (AD). However, some carriers show “clinical resilience”, maintaining their cognition despite high risk. Objective We hypothesized that the glymphatic system, the brain's waste clearance pathway, may attenuate APOE ε4-mediated neurodegeneration, and tested this in two independent cohorts. Methods We analyzed 625 cognitively normal older adults from the Alzheimer's Disease Neuroimaging Initiative (ADNI) discovery cohort and 447 amyloid-positive participants from the preclinical Anti-Amyloid Treatment in Asymptomatic Alzheimer's (A4) validation cohort. Glymphatic function was estimated using the analysis of diffusional kurtosis imaging along the perivascular space (DTI-ALPS) index in ADNI and choroid plexus (CP) 18 F-Flortaucipir PET uptake in the A4 study. Primary outcomes were clinical conversion to dementia (ADNI) and hippocampal tau pathology (A4). Results In the discovery cohort, we observed a trend toward ALPS × APOE4 interaction (p = 0.057, not reaching conventional statistical significance). Carriers with preserved function (high ALPS) showed a reduced conversion risk (hazard ratio = 0.52, 95% CI: 0.27–0.99) compared to those with low function. In the validation cohort, glymphatic interface dysfunction (higher CP tau) strongly predicted hippocampal tau burden (p < 0.0001). However, the gene-specific interaction was not replicated (p = 0.928); clearance failure predicted pathology regardless of genotype. Exploratory fluid biomarker analyses in ADNI did not reveal significant interactions. Conclusions These findings suggest that preserved glymphatic function is associated with clinical resilience in APOE ε4 carriers, though the interaction was borderline (p = 0.057) and should be considered hypothesis-generating. The strong pathological associations with clearance integrity highlight a biologically plausible mechanism in AD pathogenesis that warrants further investigation.