Studies have revealed that hypomethylation of MMP promoters can lead to increased enzyme expression in inflammatory disorders, such as MMP3, MMP9, and MMP13 in osteoarthritis chondrocytes (Roach et al., 2005), and MMP1 in RA synovial fibroblasts (Gaur et al., 2016). Here, MMP13 is linked to rheumatoid arthritis.