HDAC9 and Mental deterioration: Various studies have shown that histone modifications change at memory-related genes contribute to age and disease-related cognitive decline, and HDAC inhibitors can reverse such effects (Francis et al., 2009; Kilgore et al., 2010; Peleg et al., 2010; Graff et al., 2014; Yao et al., 2014; Benito et al., 2015; Cooper et al., 2020).