Marinova-Mutafchieva and colleagues [22] observed BMP type Ia (activin-like receptor kinase-3) receptor-positive mesenchymal cells in the synovium of RA patients, and recently we described different BMP target cells, including mostly fibroblast-like synoviocytes and the vascular-perivascular niche, in synovial biopsies of RA patients [28]. This evidence concerns the gene BMPR1A and rheumatoid arthritis.