Skeletal muscle characteristics and motor performance after 2-year growth hormone treatment in adults with Prader-Willi syndrome.

Context: In adults with Prader-Willi syndrome (PWS), abnormal body composition with decreased lean body mass (LBM) and skeletal muscle (SM) volume have been related to an altered GH secretion and may possibly contribute to a greatly reduced motor capacity. Objective: The scope of the study was to test the hypothesis that GH treatment have favourable effects on SM characteristics and motor performance in adults with PWS. Design. Setting and Participants: Fifteen PWS obese subjects (nine males and six females, age 19-35 years, BMI 37.7-59.9 kg/m2) were investigated before and after 12 (GH12) and 24 (GH24) months of GH treatment. Main Outcome Measures: SM cross sectional area (CSASM) and attenuation (ATTSM) were determined with computed tomography at lumbar and mid-thigh level. Maximal handgrip isometric strength (SHG) and isokinetic knee extension peak torque (PTKE) were measured. Motor performance was evaluated with different indoor walking tests (WT), while exercise endurance (EE) was assessed with a treadmill incremental test to exhaustion. Results: A condition of severe GH deficiency (GHD) was found in 6 patients (40%). GH treatment significantly increased LBM (GH12: p<0.05; GH24: p<0.05), reduced percentage of body fat (GH12: p<0.05; GH24: p<0.05) and augmented CSASM and ATTSM of both lumbar (GH12: p<0.01; GH24: p<0.001) and thigh muscles (GH24: p<0.05). SHG increased by 7% at GH12 (p<0.05) and by 13% at GH24 (p<0.001). PTKE extrapolated at 0 angular velocity was significantly higher at GH24 (p<0.01) and EE rose by 13% (p<0.05) and 17% (p<0.05) before exhaustion at GH12 and GH24, while no change was detected with WT. No significant difference in the response to GH treatment was detected between patients with and without GHD. Conclusion: Long term GH treatment in adult PWS patients improves body composition, muscle size and quality, and increases muscle strength and exercise tolerance independently from the GH secretory status.