Preclinical diagnosis of AD is possible if CSF Aβ42 levels decline.18 In 2018, the NIA-AA developed guidelines to group the pathological processes of AD according to Aβ deposition (A), pathological tau (T) and neurodegeneration (N) (ATN) biomarkers, resulting in a transition from a clinical to biochemical diagnosis. This evidence concerns the gene MAPT and Alzheimer disease.