We further assessed the relationship between rs393152, MAPT transcript expression levels, and medial temporal lobe atrophy separately among APOE ε4 carriers (presence of at least one ε4 allele) and non-carriers (absence of at least one ε4 allele). Using the linear mixed effects model framework described above, we found a stronger effect between rs393152 and MAPT transcript expression levels among APOE ε4 non-carriers (standardized β-coefficient = −0.22, SE = 0.04, p-value = 1.1 × 10−6) than the APOE ε4 carriers (standardized β-coefficient = −0.14, SE = 0.04, p-value = 0.001). Similarly, we found a stronger effect between rs393152 and medial temporal lobe atrophy among APOE ε4 non-carriers (entorhinal cortex: standardized β-coefficient = −0.002, SE = 0.001, p-value = 0.04; hippocampus: standardized β-coefficient = −0.003, SE = 0.001, p-value = 0.01) than among APOE ε4 carriers (entorhinal cortex: standardized β-coefficient = −0.003, SE = 0.002, p-value = 0.07; hippocampus: standardized β-coefficient = −0.003, SE = 0.002, p-value = 0.07) (Figure 5).
