An upset of this balance can lead to hypoacetylation or hyperacetylation leading to the manifestation of diseases such as cancer, inflammation, etc. Conventionally, there are 18 known human HDAC isoforms divided into four major classes (classes I, II, III and IV) depending on their homology to yeast (Saccharomyces cerevisiae) HDACs [15]. The gene discussed is HDAC9; the disease is cancer.