MAPT and Alzheimer disease: While the current well-established CSF biomarkers for AD diagnosis include Aβ1-42, phosphorylated tau 181 (P-Tau) and total tau (T-Tau) (15–17), non-Aβ or non-tau CSF biomarker, neurofilament light chain (NFL) and chitinase 3-like 1 protein (YKL-40) have also became a point of focus as alternative biomarkers for AD (25–27).