The PDGDRα+/VEGFR2- cells will be valuable for understanding not only the differentiation process from MSC progenitors to MSCs, but also the pathogenesis in cartilage and bone diseases such as fibrodysplasia ossificans progressiva and achondroplasia using the disease-derived iPSCs [45, 46]. The gene discussed is KDR; the disease is fibrodysplasia ossificans progressiva.