Restricted upper extremity range of motion in mucopolysaccharidosis type I: no response to one year of enzyme replacement therapy

Background: Mucopolysaccharidosis type I (MPS I) results from deficiency of the lysosomal enzyme alpha-L-iduronidase (IDUA). Glycosaminoglycans (GAGs) accumulate in multiple organs and the storage in connective tissues results in restricted mobility. Previous studies provided evidence of an improvement in range of motion (ROM), as measured by goniometry, after supplementation of recombinant enzyme (ERT). Aim: The aim of the study was to evaluate the efficacy of ERT in improving ROM in patients with MPS I, using a blinded three-dimensional (3D) video analysis of unrestricted movements of the upper extremities. Methods: In 6 patients with the attenuated phenotype of MPS I, the longitudinal changes in the upper extremity ROM were analysed by 3D video analysis during one year of ERT. Results: At baseline, all studied movements except for elbow flexion were restricted. No significant improvement of the restricted upper extremity ROM was observed after one year of ERT. Conclusion: Long-standing restrictions in ROM probably cannot be reversed by ERT. Early initiation of treatment might be essential to prevent irreversible functional defects.