SA2: To identify prognostic biomarkers of inflammation, bone remodeling, and cartilage turnover that can predict the progression of skeletal disease and impaired physical function in MPS I, II and VI. Our hypothesis is that biomarkers of inflammation, bone remodeling, and cartilage turnover, will be predictive of change in physical function, BMD, range of motion, hip dysplasia, kyphoscoliosis, quality of life, and height over 5 years.