HDAC9 and Other metabolic disease: HDAC11 is the singular HDAC isoenzyme in class IV and was the most recently discovered HDAC in 2002.86 It is the smallest of the HDAC enzymes and is a much more effective fatty-acid deacylase than a histone deacetylase.87 HDAC11 does not exhibit significant effects on cell proliferation but has been noted as a potential target for metabolic disorders.88 Selective inhibitors of HDAC11 have been reported,89 however as of yet, at the time of writing, no PROTACs targeting HDAC11 for degradation have been reported.