In the HUMC cohort, mediation analyses revealed that the associations of ALT levels and the AST to ALT ratio with amyloid PET positivity (total effect: ALT; β = −0.009, p = 0.003; AST to ALT ratio; β = 0.379, p < 0.001; mediating effect: ALT; β = −0.001, p = 0.158; AST to ALT ratio; β = 0.018, p = 0.360) and AD diagnosis (total effect: ALT; β = −0.001, p < 0.001; AST to ALT ratio; β = 0.456, p < 0.001; mediating effect: ALT; β = −0.00004, p = 0.468; AST to ALT ratio; β = 0.009, p = 0.750) in the APOE ε4 carrier group were not mediated by age (Figure 2 and Table 10). This evidence concerns the gene APOE and Alzheimer disease.