APOC1 and Atrophy: Although no statistically significant mediation effects were detected, HV marginally mediated the relationship between APOC1 expression and cognitive outcomes (ADNI-MEM, CDRSB), whereas no such effect was observed for APOE. These results extend our main observations by indicating that APOC1’s impact on AD-related atrophy may encompass not only cortical regions but also subcortical structures that are critically involved in memory and learning processes.