RESTING METABOLIC RATE IN PRADER-WILLI SYNDROME.

Prader-Willi syndrome (PWS) may represent a genetic form of human obesity. The purpose of this study was to determine whether the relationship between resting metabolic rate and body weight/body composition was different in patients with PWS than in obese (body mass index 23-36) and lean (body mass index 15-20) controls. We determined body composition using bioelectrical impedance analysis (BIA) and skinfold thickness measurements in 36 subjects with PWS and in 31 controls (20 nonobese, 11 obese). The BIA measures of percentage of body fat were significantly correlated with those determined from skinfold thicknesses in all three groups. Resting metabolic rate (RMR) was measured in all lean and obese controls and in 22 of the 36 patients. Energy expenditure was compared among groups by comparing the regression relationship between RMR and either body weight or fat-free mass (FFM). The relationship between RMR and body weight and between RMR and FFM was different for patients with PWS than for lean and obese controls, who did not differ from each other. The nature of the relationship was such that patients with PWS had reduced rates of energy expenditure compared to controls, except for patients with the largest body mass and FFM. This suggests that a low energy expenditure exists initially for persons with PWS but may return to normal as obesity becomes greater. These results also suggest that reduced FFM is not the sole explanation for the lower energy expenditure seen in patients with PWS.