The mood stabilizing effect of sodium valproate, a potent histone deacetylase (HDAC) inhibitor known to indirectly influence DNA methylation [46], [47] via chromatin modification and used in the treatment of bipolar disorder, and the noted antidepressive effect of S-adenosyl methionine, a methyl donor in the DNA methylation reaction and an inhibitor of active demethylation [48] , suggest a role for DNA methylation in mood regulation [49]. Here, HDAC9 is linked to bipolar disorder.