Compared with control, the protein levels of SETDB1 and its substrate H3K9me3 are obviously increased in the striatal neurons of Huntington’s disease patients and transgenic R6/2 (a Huntington’s disease mouse model) mice, and both specificity protein 1 (Sp1) and Sp3 can bind to the Setdb1 promoter to activate the transcription of Setdb1 gene [36]. The gene discussed is SP1; the disease is Huntington disease.