MAPT and Alzheimer disease: We assessed the relationship between BBB biomarkers (total protein, CSF and serum albumin, the CSF/serum albumin ratio (Qalb), serum and CSF IgG, and the IgG index), CSF markers of AD (Aβ42, Aβ40, Aβ42/40 ratio, p-tau, and t-tau), age, sex, ApoE status, and cognitive status.