Among the 194 patients without arthritis, 63 underwent measurement of serum MMP-3 during the subacute phase of KD, and the median serum MMP-3 concentration was 33.9 ng/mL (IQR, 27.8–44.3 ng/mL), which was significantly lower than the serum MMP-3 concentration of patients with persistent arthritis (p < 0.001). The gene discussed is MMP3; the disease is arthritic joint disease.