In the ADNI cohort, mediation analyses revealed that the associations of ALT levels and the AST to ALT ratio with amyloid PET global SUVR (total effect: ALT; β = −0.006, p = 0.002; AST to ALT ratio; β = 0.178, p = 0.012; mediating effect: ALT; β = −0.0002, p = 0.464; AST to ALT ratio; β = 0.013, p = 0.416) and AD diagnosis (total effect: ALT; β = −0.013, p = 0.009; AST to ALT ratio; β = 0.189, p = 0.009; mediating effect: ALT; β = 0.0001, p = 0.922; AST to ALT ratio; β = 0.005, p = 0.806) were not mediated by age in the APOE ε4 carrier group (Figure 3 and Table 11). Here, GPT is linked to Alzheimer disease.