A highly sensitive LC-MS/MS protocol was introduced for the quantitative measurement of amyloid-β (Aβ) species in cerebrospinal fluid (CSF) for clinical evaluation of Alzheimer’s disease (AD) patients [179], as well as for quantifying plasma Aβ1-40 and Aβ1-42 peptides and apolipoprotein E (APOE) for the assessment of brain amyloidosis [180]. Here, APOE is linked to Alzheimer disease.