Isokinetic muscle strength differences in patients with mucopolysaccharidosis I, II, and VI

PURPOSE: To determine muscular strength differences in patients with MPS-I, II, and VI versus age-and sex-matched healthy controls. METHODS: Dominant leg isokinetic knee extension strength was measured at 90 and 120 degrees per second (d/s) using a dynamometer in 30 subjects with MPS and 42 controls (5-16 yrs). MPS-I was further divided into MPS-IA (attenuated) and MPS-IH (severe). Strength measures analyzed were peak torque (PkT), peak torque per unit body weight (PkT/BW) and per unit lean body mass (PkT/LBM), and average power (AP). RESULTS: Following adjusting strength measures for age, MPS-IH and MPS-II had significantly lower strength measures for all variables at both angular velocities. MPS-VI had significantly lower PkT, PkT/LBM, and AP compared to controls at 90 and 120d/s. In contrast, MPS-IA was not significantly different from controls for any strength variable at either angular velocity. CONCLUSION: The results of this study suggest that decrements in skeletal muscle strength depend on MPS diagnosis and severity of disease. Children with MPS-IH demonstrate the greatest difference in muscular strength compared to healthy controls.