MMP9 and osteoporosis: Inconsistent with the results of many studies conducted on bone turnover and osteoporosis risk in MPS patients, this study supports the finding of high levels of MMP2, MMP9, TIMP1, TIMP2, and low levels of cathepsin K in MPS IIIB patients, indicating that their bone density is low and their risk of bone turnover or osteoporosis is increased [12,23–33].