In the aged HD mice, chromatin-relaxing lysine methyltransferases, such as Setd2 (H3K36-specific), Ash1l (H3K4), and Prdm9 (H3K4), were upregulated whereas chromatin-packing enzymes, such as Ezh2 (H3K27) and Setdb1 (H3K9), were downregulated (Fig. 5B). This evidence concerns the gene PRDM9 and Huntington disease.