Osteoporosis has been described in animal models of MPS. It is unknown whether abnormalities seen in animal models of MPS can be extrapolated to osteoporosis or increased risk of fracture in children and adults affected with MPS. Preliminary data suggest that children and adolescents with MPS I, II and VI have low bone mineral density (BMD) after adjustment for short stature and abnormal bone geometry and that markers of bone remodeling are cross-sectionally associated with BMD. It is unknown whether this decreased BMD during childhood will result in osteoporosis and increased fracture risk in adulthood. Determining the risk for osteoporosis in MPS I, II and VI has become particularly important as these individuals are now healthier and more mobile with new and improved treatments and thus have a greater opportunity for fracture.