In the APOE ε4+ AD group, the level of serum IgA significantly and positively predicted CSF Aβ42 level (β = 43.75, B/H adjusted p = 0.011), the level of plasma TG significantly and negatively predicted CSF t‐tau level (β = −101.83, B/H adjusted p < 0.001) and CSF p‐tau 181 level (β = −14.76, B/H adjusted p < 0.001) (Figure 5A–C). This evidence concerns the gene MAPT and Alzheimer disease.