ACP5 and familial avascular necrosis of femoral head: Although TRAP was expressed to a certain extent in the new bones located in AS-joint tissues (Fig. 4g), RPS17 fluorescence expression in bone-surface-OCPs (displayed as RPS17-RANK overlapping fluorescence) was significantly weaker than that in subchondral bones of non-AS patients with ANFH (Figs. 4h and S8c), inferring that abnormal RPS17 expression exists in AS-joints, resulting in insufficient abundance of osteoclasts to absorb new bones.