HDAC6 and Alzheimer disease: To elucidate the role of HDAC6 in AD, Hdac6−/− mice were crossed with APPPS1-21 mice (to yield APPPS1-21-Hdac6−/− mice), which is a model for severe amyloid pathology that shows memory impairment at 8 months of age (Govindarajan et al, 2011; Radde et al, 2006).