DKK3 and rheumatoid arthritis: The amplified S2d SF subset in RA expresses genes critical for joint pathology, including the extracellular matrix component fibulin 7 (Fbln7), vascular remodeler collagen triple helix repeat containing 1 (Cthrc1), Wnt inhibitor Dkk3, novel mesenchymal protein Lrrc15, and transcription factor Runx1 [12].