Using PET quantification that assesses the proteomic differences in the serum composition among AD patients, patients with cognitive impairment, and healthy individuals, numerous proteins, such as proprotein convertase subtilisin/kexin type 9 (PCSK9), coagulation factor XIII A1 subunit (F13A1), and donation after cardiac death (DCD), have been identified as potential markers for amyloid deposition. Here, PCSK9 is linked to Alzheimer disease.