The associations of AD diagnosis with ALT (total effect: β = −0.013, p = 0.017; mediating effect: β = −0.007, p = 0.002) and the AST to ALT ratio (total effect: β = 0.184, p = 0.032; mediating effect: β = 0.106, p = 0.024) were significantly mediated by amyloid PET global SUVR, indicating a notable indirect effect in the APOE ε4 carrier group. The gene discussed is GPT; the disease is Alzheimer disease.