Body composition in Prader-Willi syndrome compared with nonsyndromal obesity: Relationship to physical activity and growth hormone function

Objective: To study the relationship of fat mass, extracellular-to-intracel lular-water ratio, and bone mineral density with growth hormone function an d physical activity in Prader-Willi syndrome. Study design: There were 17 patients with PWS (10 women, ages 7.5-19.8 year s) and 17 obese control patients, matched for gender and bone age. FM and e xtracellular-to-intracellular-water ratio were measured by bromide-deuteriu m dilution, BMD by dual-energy x-ray absorptiometry, GH function by fasted serum insulin-like growth factor-I concentration, and physical activity by doubly-labeled water in combination with basal metabolic rate by a ventilat ed hood. Results: The PWS group had a similar fat mass, but a lower fat-free mass, w hereas the extracellular-to-intracellular-water ratio was higher, compared with the control group (0.87 +/- 0.07 l/l and 0.80 +/- 0.06 l/l, respective ly [P < .01]). Fat mass was inversely related with PA in the PWS group, whe reas IGF-I was positively correlated with FFM, ICW, and BMD of the limbs. B MD tended to be lower in patients with PWS. Conclusions: In children and adolescents with PWS, adiposity is associated with a reduced fat-free mass and extracellular-to-intracellular-water-ratio is increased. Both Findings are related to GH function and physical activi ty. BMD, especially in the limbs, tends to be reduced in patients with PWS and is related to GH function.