Diurnal oscillation of CSF Aβ and other AD biomarkers

To assess stages of Alzheimer's disease (AD) pathogenesis and the efficacy of drugs during clinical trials, there has been immense interest in the field to establish baseline cerebrospinal fluid (CSF) concentrations for potential AD biomarkers such as amyloid-beta (A beta) and tau. Significant within-person variations in CSF A beta concentrations over time found that this variation followed the sleep-wake cycle. A recent paper in Molecular Neurodegeneration reported the absence of diurnal variations in multiple classical and candidate AD biomarkers, such as soluble APP, A beta, tau, p-tau, YKL-40, VILIP-1, or apolipoprotein E. This commentary addresses these apparently discordant results regarding the diurnal variability of APP and A beta compared with the literature. Despite our concerns, we appreciate the authors' interest in this important topic and contribution to improve our knowledge about the factors influencing A beta diurnal variation.