Indeed, the transcription factor MITF is essential to osteoclast development and maturation(53) and also known to bind to the promoter of DC‐STAMP, a major transmembrane protein involved in osteoclast fusion and multinucleation.(54) Although further mechanistic study is needed, one explanation for reconciling these data may involve factors known to repress MITF expression and to stimulate osteoclast formation as well, such as ATF4.(55, 56) The expression profiles also suggest increases in CD38 expression in mature osteoclasts of erosive RA. This evidence concerns the gene ATF4 and rheumatoid arthritis.