Amyloid beta peptide 1-42 to 1-40 ratio (Aβ42/40 ratio)

The amyloid beta peptide 1-42 to 1-40 ratio (Aβ42/40 ratio) is a quantitative biomarker used in research and diagnosis of Alzheimer’s disease. It is obtained by dividing the concentration of the 1-42 amino acid isoform of amyloid beta by the concentration of the 1-40 isoform in a biological fluid (usually plasma or CSF). Both peptides are produced via proteolytic cleavage of amyloid precursor protein (APP); however, Aβ42 is more prone to aggregation and more neurotoxic than Aβ40. In Alzheimer’s disease, the relative amount of Aβ42 decreases in plasma/CSF due to deposition in plaques, while Aβ40 levels are less affected. A lowering of the Aβ42/40 ratio is thus indicative of increased cerebral amyloid plaque burden and supports diagnosis or risk stratification for Alzheimer’s disease. The test reduces reliance on invasive procedures such as lumbar puncture or costly PET imaging for AD diagnosis and is widely used for patient selection and efficacy monitoring in clinical trials. Key points: - Not a drug target, but a widely used diagnostic and research biomarker - Reflects pathological amyloid deposition, central to Alzheimer’s disease progression - Influenced by, but does not itself interact directly with, drugs targeting amyloid production, aggregation, or clearance

Other names

Aβ42/40 ratioBeta-amyloid 1-42/1-40 ratioAmyloid-beta 42/40 ratioBeta-amyloid ratio

Not applicable for the ratio itself. Drugs may work by inhibiting amyloid beta production (β- or γ-secretase inhibitors), preventing its aggregation, or promoting clearance.