Their cellular functions are related to regulation of transcription, cell differentiation, migration and inflammation.14–16 HDAC class I and class II are Zn2+ dependent enzymes, in contrast to class III enzymes that are NAD+ dependent.11,17,18 Class III members are SIRT1-7 and their functions are linked to metabolism, stress response, aging, and cell cycle.14,19 HDAC11 was considered as the sole member of a distinct class known as HDAC class IV.20 It was found to be Zn2+ dependent and highly associated with obesity, tumor growth, and prognosis.21,22. Here, HDAC9 is linked to obesity due to melanocortin 4 receptor deficiency.