Body Composition by DXA in Patients With Klinefelter and Kallmann Syndrome: The Kama Study

Abstract Context Klinefelter syndrome and Kallmann syndrome are two rare genetic disorders characterized by reduced testosterone levels but differing in their gonadotrophin profiles. To date, no studies have directly compared body composition in these two syndromes. Objective To assess the prevalence of altered body composition parameters in patients with Klinefelter and Kallmann syndromes and to compare body composition between the two groups. Secondary objectives included evaluating associations between body composition, bone mineral density (BMD), and serum follicle-stimulating hormone (FSH) levels. Methods This single-centre, retrospective observational study included 50 patients, 29 with Klinefelter and 21 with Kallmann syndrome receiving testosterone replacement therapy. Body composition was evaluated using whole-body Dual-Energy X-ray Absorptiometry (DXA), which provided measurements of Appendicular Lean Mass (ALM), Total Body Fat (TBF), Visceral Adipose Tissue (VAT), the ALM-to-height² ratio (Appendicular Lean Mass Index, ALMI), and the ALM-to-weight ratio. Results Radiologic sarcopenic obesity was identified in 7 patients (14%; 6/29 Klinefelter, 1/21 Kallmann), while osteosarcopenic obesity was found in 2 patients (4%), both with Klinefelter syndrome. Patients with Kallmann syndrome had significantly higher ALMI values than those with Klinefelter syndrome (8.37 ± 1.15 vs. 7.28 ± 1.20 kg/m², p0.001). Univariable analysis revealed an inverse association between FSH levels and ALMI (B = –0.026; p = 0.002), which remained significant after adjustment for confounders (B = –0.030; p = 0.0022). Conclusions This study demonstrated a significant difference in lean mass between Klinefelter and Kallmann syndromes, supporting a potential role for FSH in modulating muscle mass independently of testosterone levels.