NRGN and Alzheimer disease: Thus, the Aβ-GAPDH complexes may serve as a reliable biomarker of AD progression, comparable to other already established markers like CSF amyloid beta 42 (Aβ42), total tau (t-tau), and tau phosphorylated at threonine 181 (p-tau [43], or recently proposed ones like neurogranin/β-site APP-cleaving enzyme 1 (Ng/BACE1) [44].