MAPT and Alzheimer disease: Similarly, both sAPPα (r = 0.628, p < 0.0001) and sAPPβ (r = 0.540, p < 0.0001) were positively correlated with total tau among all patients (Additional file 2: Figure S2) as well as among AD and MCI-AD groups (sAPPα: r = 0.577, p = 0.0001; sAPPβ: r = 0.359, p = 0.023) and other groups (sAPPα: r = 0.391, p = 0.01; sAPPβ: r = 0.349, p = 0.024).