Patients who have an earlier diagnosis of MPS are likely to have better health outcomes with medical management. Therefore, it is important to determine effective diagnostic methods. Investigators believe that bilateral hip involvement should alert the clinician to the possibility of MPS VI and further examination. The purpose of this study is to test the hypothesis that the correct diagnoses of two MPS storage disorders are delayed in patients with bilateral proximal femoral epiphyseal dysplasia and normal quantitative urine MPS studies.