A recent paper in Molecular Neurodegeneration reported the absence of diurnal variations in multiple classical and candidate AD biomarkers, such as soluble APP, Aβ, tau, p-tau, YKL-40, VILIP-1, or apolipoprotein E. This commentary addresses these apparently discordant results regarding the diurnal variability of APP and Aβ compared with the literature. This evidence concerns the gene MAPT and Alzheimer disease.