HDAC9 and 2q37 microdeletion syndrome: In addition, HDAC loss-of-function mutations are linked to neurodevelopmental disorders, as observed with HDAC3 in Huntington's disease (HD) (Jia et al. 2016), HDAC4 in brachydactyly mental retardation syndrome (BDMR) (Williams et al. 2010), and HDAC8 in Cornelia de Lange syndrome (CdLS) (Fig. 4; Kaiser et al. 2014).