d-β-Hydroxybutyrate (DβHB), an endogenous HDAC inhibitor of class I HDACs, showed neuroprotective effects in the 3-nitropropionic acid (3-NP) toxic mouse model of HD and in R6/2 transgenic mice, ameliorating histone hypoacetylation and improving locomotor activity and premature death [104]. The gene discussed is HDAC9; the disease is Huntington disease.