Normal bone mineral content but unfavourable muscle/fat ratio in Klinefelter syndrome

Objective: To evaluate body composition and bone mineral content (BMC) in children and adolescents with Klinefelter syndrome (KS). Design: Retrospective cross-sectional study. Setting: Tertiary endocrine clinic at the University Hospital, Copenhagen. Patients: Eighteen untreated boys with KS and six boys with KS receiving androgen substitution with a median age of 11.0 years (range 4.3-18.6) participated in the study. Intervention: Dual energy x ray absorptiometry and anthropometric measurements were analysed. Main outcome measures: Lumbar and whole body BMC, lean body mass (LBM), body fat mass (BFM), body fat percentage (BF%), height and body mass index (BMI) were compared between treated and untreated boys with KS and compared to normal age-matched boys. Results: LBM (untreated -0.3 (-2.4 to +2.1) and treated +1.1 (-1.6 to +2.1)) was normal, while BFM (untreated +0.5 (-1.0 to +2.3), p = 0.02 and treated +1.6 (-0.2 to +2.4), p =0.01) was significantly increased, all expressed as standard deviation scores. Lumbar bone mineral density (BMD; untreated -0.4 (-3.1 to +0.9) and treated +1.0 (-1.4 to +3.0)) and whole body BMC (untreated +0.1 (-1.8 to +3.3) and treated +1.5 (-1.1 to +2.5)) were normal. Conclusion: We found significantly increased BFM and BF% despite normal LBM, suggesting the presence of an unfavourable muscle/ fat ratio. Lumbar BMD and whole body BMC were normal. These findings suggest that the unfavourable metabolic profile seen in adult KS may already be present in childhood as evidenced by the increased fat mass, whereas the reported low BMD seems to develop after puberty.