Immuno-Affinity purification (IP) MS method developed to measure Aβs; Aβ1–40 and Aβ1–42) and Aβ approximate peptides. APP/Aβ (−3–40)/Aβ1–42 ratio was increased in amyloid PET-positive AD patients and was proposed as biomarker to surrogate cerebral amyloid deposition. The gene discussed is APP; the disease is Alzheimer disease.