We developed a novel immunoassay to detect p-tau T217 in the CSF, and subsequently undertook this study to (1) evaluate the sensitivity and specificity of the p-tau T217 assay using AD and non-AD CSF samples from 3 international cohorts of patients; (2) compare its sensitivity and specificity with standard CSF measures (particularly with total tau [t-tau], p-tau T181, Aβ40, and Aβ42); and (3) assess the relationship between the levels of p-tau T217 with the above-mentioned standard CSF biomarkers. The gene discussed is MAPT; the disease is Alzheimer disease.