Aβ peptides (Aβ42 and Aβ40) and p-tau can be quantified in cerebrospinal fluid (CSF) and, more recently, in blood, where both biomarkers show high accuracy in determining underlying AD brain pathology1 in both symptomatic2,3 and asymptomatic disease.4,5 When using these biomarkers in studies focusing on disease mechanisms or treatment effects, it is important to understand the differences between biomarker changes observed in CSF and blood relating to the proposed underlying pathophysiology. Here, MAPT is linked to Alzheimer disease.