For example, in patients with rheumatoid arthritis, DNA hypomethylation of HDAC1 (histone deacetylase 1) and HDAC2 levels, hyperacetylation of histones H3 and H4, and hypomethylation of histone H3 at lysine 9 have been observed in synovial tissues. This evidence concerns the gene HDAC1 and rheumatoid arthritis.