In the research framework of AD, CSF tau is one of the core markers of the so called “ATN system,” where “A” refers to the value of an amyloid β biomarker (amyloid PET or CSF Aβ42); “T,” the value of a tau pathology biomarker (CSF p-tau or tau PET); and “N,” a quantitative or topographic biomarker of neurodegeneration or neuronal injury (112, 113). Here, MAPT is linked to Alzheimer disease.