MAPT and Alzheimer disease: Graff et al. (2012) found that histone deacetylase 2 (HDAC2) expression in the hippocampus of AD patients increased. Its overexpression may be related to dendritic spine density, decreased number of synapses, synaptic plasticity, and memory (Graff et al., 2012). Another study also found that HDAC2 overexpression induced AD-like tau hyperphosphorylation and aggregation, which were accompanied by a loss of dendritic complexity and spine density (Liu et al., 2017).