APP and Alzheimer disease: It's important to note that while Amyloid Precursor Protein (APP) itself is not a biomarker, the cleaved fragments, especially Aβ (1−40) and Aβ (1−42), are widely used as biomarkers to detect and characterize AD.Additionally, the Aβ1–40/Aβ1–42 ratio serves as another valuable biomarker in AD, offering insights into the amyloid burden in the brain and aiding in the diagnostic process (Atwood et al., 2000a).