MMP3 and juvenile idiopathic arthritis: The normal MMP-3 concentration range in children is unclear, although Matsuyama et al. showed that the median MMP-3 concentration in healthy children is 12.0 ng/mL (range, 5–18 ng/mL)19, and Japanese clinical practice guidelines for JIA indicate a lower concentration compared with adults (< 15.0 ng/mL)20.