Our findings show a significant increase of cathepsin S both at the synovium and PBMCs of patients with RA which is significantly associated with the expression of ADAR1 and especially of ADAR1p150, as well as with the individual RNA editing rate of the adenosines located within the AluSx+ of cathepsin S 3′ UTR. The gene discussed is CTSS; the disease is rheumatoid arthritis.