Peculiar body composition in patients with Prader-Labhart-Willi syndrome

Prader-Labhart-Willi syndrome (PWS)-characterized by severe obesity, short stature, hypogonadism, and muscle hypotonia-appears to be an interesting model for body-composition abnormalities. Twenty-seven PWS patients (15 males and 12 females) aged 6-22 y underwent total-body analysis by dual-energy X-ray photon absorptiometry (DXA). For each PWS patient two age- and sex-matched control subjects were studied: one obese subject with a relative body weight (RBW > 120%) and body mass index (BMI) similar to that of the patient and one normal-weight subject (RBW < 120%). Percentage body fat was significantly greater in PWS patients than in obese subjects (47.4 +/- 7.2% compared with 41.9 +/- 9.9%, P < 0.0001) and the same difference was evident for arms and legs but not for the trunk. Lean mass was significantly lower in PWS patients (26.4 +/- 8.2 kg) than in normal-weight subjects (32.9 +/- 10.2 kg) and even more so than in obese subjects (40.3 +/- 13.2 kg) (P < 0.0001). The most affected regions were limbs; thus, the ratio of lean mass in the trunk to that in the limbs was significantly higher in PWS patients (1.19 +/- 0.15) than in obese (1.07 +/- 0.13) and normal-weight (1.07 +/- 0.09) subjects (P < 0.002). The ratio of fat mass to lean mass was significantly higher in PWS patients than in obese subjects (0.90 +/- 0.32 and 0.74 +/- 0.27, P < 0.05). Bone mineral content (BMC) was significantly lower in PWS patients (1503 +/- 46 g) than in normal-weight (1876 +/- 677 g) and obese (2322 +/- 773 g) subjects (P < 0.0001); this difference was most pronounced in the limb region. Bone mineral density (BMD) in PWS patients (0.993 +/- 0.116 g/cm2) did not differ significantly from that of normal-weight subjects (1.033 +/- 0.147 g/cm2) but was significantly lower than that of obese subjects (1.154 +/- 0.139 g/cm2). The influence of age on body composition was assessed by comparing two age subgroups (< 12 y, n = 10; and > or = 12 y, n = 17). The older PWS patients had higher adiposity, lower BMC, and dramatically lower BMD. Also, the lean mass deficit increased with age so that the ratio of fat mass to lean mass was close to 1. In conclusion, PWS patients showed a peculiar body composition, to some extent similar to that found in subjects deficient in growth hormone or even to sedentary and elderly people. These results suggest the importance of an accurate analysis of body composition in PWS patients.