HDAC9 and Familial prostate cancer: 2013). Co-activators such as KAT5 (lysine acetyltransferase 5) and co-repressors such as the HDAC family bind the AR complex to facilitate or prevent the transcription of AR target genes via their respective histone acetyl transferase (HAT) or histone deacetylase (HDAC) activities (Fu et al. 2000; Korkmaz et al. 2004; Dai et al. 2007). Moreover, altered AR histone modification profiles have been reported in prostate cancer (Seligson et al. 2005).