CLOCK and Alzheimer disease: Collectively, the mixed result of these and other studies raises the following possibilities: 1) the inherent clock timing properties of the SCN are not markedly affected by Aβ- or tau-mediated pathologies, 2) that transgenic mouse lines do not effectively model the SCN-centric circadian disruptions observed in AD patients, or 3) that the locus of the clock disruption in AD occurs largely outside of the SCN.