In our previous work we have shown the utility of using two well-established cerebrospinal fluid (CSF) biomarkers for AD, 42 amino acid fragments of amyloid beta (Aβ42; decreased in AD) and tau phosphorylated at threonine 181 (a proxy for hyperphosphorylated tau; ptau181; increased in AD), as endophenotypes for genetic studies of AD [14], [15], [16], [17]. Here, MAPT is linked to Alzheimer disease.