In a previous study, researchers found that Aβ 42/40 ratio outperformed Aβ42 alone in differentiating AD from non-AD patients, but the diagnostic performance of the combination of CSF tau and CSF Aβ42 was not improved by the use of Aβ 42/40 ratio instead of Aβ42 alone [15]. This evidence concerns the gene MAPT and Alzheimer disease.