Lean Body Mass in Boys With Prader-Willi Syndrome Increases Normally During Spontaneous and Induced Puberty

Abstract Context Prader-Labhart-Willi syndrome (PWS) is a rare genetic disorder characterized by intellectual disability, behavioural problems, and hypothalamic dysfunction combined with specific dysmorphisms. In PWS, growth hormone treatment is given primarily to improve body composition, yet lean body mass (LBM) does not normalize. Male hypogonadism is frequent in PWS and becomes evident during puberty. While LBM increases in normal boys during puberty, it is not known whether LBM and muscle mass concomitantly increase in PWS during spontaneous or induced puberty. Objective To describe the peripubertal increment in muscle mass in boys with PWS undergoing growth hormone treatment. Design Single-center, retrospective descriptive study, using data from 4 years before until 4 years after onset of puberty. Setting Primary referral centre for PWS. Patients Thirteen boys diagnosed with genetically proven PWS. The mean age at onset of puberty was 12.3 years; the mean observation period before (after) onset of puberty was 2.9 (3.1) years. Intervention Puberty was induced upon pubertal arrest. All boys received internationally standardized growth hormone treatment. Main Outcome Measure Lean mass index (LMI) determined by dual energy X-ray absorptiometry. Results LMI increased by 0.28 kg/m2 per year before puberty and by 0.74 kg/m2 per year after the onset of puberty. The time before puberty explained less than 10% of the variation in LMI, whereas the time after puberty onset explained about 25%. Conclusion Boys with PWS showed a recognizable increment in LMI during both spontaneous and induced puberty compared with the prepubertal phase, which was within the trajectories of normal boys. Therefore, timely testosterone substitution in the absence or at arrest of puberty during growth hormone treatment is important to optimize peak LBM in PWS.