APOE and Alzheimer disease: Multiple studies on biomarkers related to Alzheimer’s disease (AD) have shown that the carrier rate of apolipoprotein E (APOE) ε4 genes in SCD patients is significantly higher than that in HC, and that amyloid-β (Aβ) and tau protein have already begun to aggregate during the SCD stage, with the extent of their deposition positively correlating with the severity of cognitive impairment in patients (Bolton et al., 2024; Pérez-Cordón et al., 2020; Wang et al., 2020).