BACKGROUND/OBJECTIVE: Quantitative urine screening for mucopolysaccharides (MPS) has been the primary method for detecting mucopolysaccharidoses in children. This method may not be sufficiently sensitive and may miss some patients with arylsulfatase B (ARSB) deficiency. Investigators propose to identify patients retrospectively and prospectively who carry a diagnosis of spondyloepiphyseal dysplasia, multiple epiphyseal dysplasia, bilateral proximal femoral epiphyseal dysplasia, or bilateral Legg-Calve-Perthes. For these patients, investigators will perform enzyme testing on a blood sample which will identify MPS VI or IVA.