For example, in AD, tau phosphorylated at T181 (p-tau181) and unphosphorylated, so called “total-tau” (t-tau) are routinely measured by immunoassays; however, the ELISA p-tau181/t-tau ratio does not report the changes in the phosphorylation rate due to the nearly identical information provided by the phospho-tau181 and t-tau ELISA assays (correlations >0.95). Here, MAPT is linked to Alzheimer disease.