For HDAC, both AS and RA had decreased levels of activity, and again the difference was only significant between AS and HC (AS vs RA vs HC: 1984.6 ± 249 vs 3915.9 ± 790.3 vs 4778.9 ± 752.3 pmol/min/mg; AS vs HC: p = 0.01; RA vs HC: p > 0.05) (Table 2, Figure 1B). Here, HDAC9 is linked to rheumatoid arthritis.