We performed Western blot analysis (control: n = 3; LCPD: n = 5) and found that the resulting optical density of HMGB1 protein was significantly higher in the synovial fluid of patients with LCPD than that of controls (relative HMGB1 values: LCPD 9.91 ± 4.04 versus control 0.77 ± 0.27, p < 0.01; Fig. 1A,B). The gene discussed is HMGB1; the disease is Legg-Calve-Perthes disease.