SFRP4 and rheumatoid arthritis: In a rat model of rheumatoid arthritis (RA), the overexpression of Mecp2 has been associated with epigenetic repression of SFRP4 (Secreted Frizzled Related Protein 4) and increased WNT pathway activity, which contributes to RA pathophysiology by inducing synovial hyperplasia, inflammation, pannus formation, and cartilage erosion [76].