HDAC9 and bipolar disorder: Several epigenetic drugs have already been used in other diseases, such as histone deacetylase (HDAC) inhibitors like suberoylanilide hydroxamic acid (SAHA), vorinostat, for skin T-cell lymphoma, Valproic Acid (VPA) for epilepsy and bipolar disorder, and DNA methylation inhibitors like decitabine for myelodysplastic syndromes and acute myeloid leukemia [37].