Physical performance testing in mucopolysaccharidosis I: a pilot study

To develop and field-test a physical performance measure (MPS-PPM) for individuals with Mucopolysaccharidosis I (MPS I), a rare genetic disorder.Motor performance and endurance items were developed based on literature review, clinician feedback, feasibility, and equipment and training needs. A standardized testing protocol and scoring rules were created. The MPS-PPM includes: Arm Function (7 items), Leg Function (5 items), and Endurance (2 items). Pilot data were collected for 10 subjects (ages 5-29 years). We calculated Spearman's rho correlations between age, severity and summary z-scores on the MPS-PPM.Subjects had variable presentations, as correlations among the three sub-test scores were not significant. Increasing age was related to greater severity in physical performance (r = 0.72, p0.05) and lower scores on the Leg Function (r = -0.67, p0.05) and Endurance (r = -0.65, p0.05) sub-tests. The MPS-PPM was sensitive to detecting physical performance deficits, as six subjects could not complete the full battery of Arm Function items and eight subjects were unable to complete all Leg Function items. Subjects walked more slowly and expended more energy than typically developing peers.Individuals with MPS I have difficulty with arm and leg function and reduced endurance. The MPS-PPM is a clinically feasible measure that detects limitations in physical performance and may have potential to quantify changes in function following intervention.