CLN5 and rheumatoid arthritis: We propose that BMPs would play a dual role in the synovium, controlling the production of pro-inflammatory cytokines and inhibiting synoviocyte transformation in healthy and non-inflammatory conditions, but in advanced stages of RA could contribute to chronic inflammation, allowing the functional deregulation of synoviocytes and promoting the activation and pro-inflammatory functions of immune and non-immune cells accumulating in the inflamed arthritic joint.