APP and Cognitive impairment: LDL-C: low-density lipoprotein cholesterol; HDL-C: high-density lipoprotein cholesterol; TC: total cholesterol; TG: triglycerides; AD: Alzheimer's disease; Apo: apolipoprotein; Aβ: beta-amyloid; APP: amyloid precursor protein; MCI: mild cognitive impairment; BBB: blood-brain barrier; 24S HC: 24S hydroxycholesterol; 27O-HC: 27O hydroxycholesterol; PSEN: presenilin; ABCA1 and ABCA7: ATP binding cassette transporter 1 and 7; CYP46A1: cytochrome P450 family 46 subfamilies A member 1