PECULIAR BODY-COMPOSITION IN PATIENTS WITH PRADER-LABHART-WILLI-SYNDROME

Prader-Labhart-Willi syndrome (PWS)-characterized by severe obesity, s hort stature, hypogonadism, and muscle hypotonia-appears to be an inte resting model for body-composition abnormalities. Twenty-seven PWS pat ients (15 males and 12 females) aged 6-22 y underwent total-body analy sis by dual-energy X-ray photon absorptiometry (DXA). For each PWS pat ient 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 (RB W < 120%). Percentage body fat was significantly greater in PWS patien ts 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 patient s (1.19 +/- 0.15) than in obese (1.07 +/- 0.13) and normal-weight (1.0 7 +/- 0.09) subjects (P < 0.002). The ratio of fat mass to lean mass w as 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 s ignificantly lower in PWS patients (1503 +/- 46 g) than in normal-weig ht (1876 +/- 677 g) and obese (2322 +/- 773 g) subjects (P < 0.0001); this difference was most pronounced in the limb region. Bone mineral d ensity (BMD) in PWS patients (0.993 +/- 0.116 g/cm(2)) did not differ significantly from that of normal-weight subjects (1.033 +/- 0.147 g/c m(2)) but was significantly lower than that of obese subjects (1.154 /- 0.139 g/cm(2)). The influence of age on body composition was assess ed by comparing two age subgroups (< 12 y, n = 10; and greater than or equal to 12 y, n = 17). The older PWS patients had higher adiposity, lower BMC, and dramatically lower BMD. Also, the lean mass deficit inc reased with age so that the ratio of fat mass to lean mass was close t o 1. In conclusion, PWS patients showed a peculiar body composition, t o some extent similar to that found in subjects deficient in growth ho rmone or even to sedentary and elderly people. These results suggest t he importance of an accurate analysis of body composition in PWS patie nts.