Body Composition Differences in Klinefelter vs Kallmann Syndromes via DXA
Overview
This study compared body composition in 50 hypogonadal men with Klinefelter (n=29) and Kallmann (n=21) syndromes using DXA. Patients with Kallmann syndrome exhibited significantly higher appendicular lean mass index (ALMI) than those with Klinefelter syndrome. An inverse association between serum FSH levels and ALMI was identified, suggesting FSH may modulate muscle mass independently of testosterone.
Background
Klinefelter and Kallmann syndromes are rare genetic disorders characterized by low testosterone but differing gonadotrophin profiles and genetic backgrounds. Both conditions are associated with altered body composition, including changes in muscle and fat mass, which impact bone mineral density (BMD) and overall musculoskeletal health. Osteosarcopenic obesity, the coexistence of low BMD, reduced muscle mass, and obesity, is a clinical concern due to increased risks of falls and fractures. The role of follicle-stimulating hormone (FSH) in modulating body composition and bone metabolism is increasingly recognized but not fully understood.
Data Highlights
Parameter
Klinefelter Syndrome (n=29)
Kallmann Syndrome (n=21)
P Value
Appendicular Lean Mass Index (ALMI, kg/m²)
7.28 ± 1.20
8.37 ± 1.15
< .001
Radiologic Sarcopenic Obesity (n, %)
6 (21%)
1 (5%)
Not specified
Osteosarcopenic Obesity (n, %)
2 (7%)
0 (0%)
Not specified
Key Findings
Patients with Kallmann syndrome had significantly higher ALMI compared to those with Klinefelter syndrome (8.37 vs 7.28 kg/m²; P < .001).
Radiologic sarcopenic obesity was more prevalent in Klinefelter syndrome (21%) than in Kallmann syndrome (5%).
Osteosarcopenic obesity was identified only in Klinefelter patients (7%).
Serum FSH levels inversely correlated with ALMI (B = −0.030; P = .0022) after adjusting for confounders.
Differences in lean mass between the syndromes suggest FSH may influence muscle mass independently of testosterone levels.
Clinical Implications
Clinicians should recognize that despite testosterone replacement, patients with Klinefelter syndrome may have lower muscle mass and higher prevalence of sarcopenic obesity compared to those with Kallmann syndrome. Monitoring body composition using DXA can aid in identifying patients at risk for osteosarcopenic obesity and related complications. The inverse relationship between FSH and muscle mass highlights the potential need to consider gonadotrophin profiles when managing hypogonadal patients.
Conclusion
This study highlights significant differences in body composition between Klinefelter and Kallmann syndromes, emphasizing a potential modulatory role of FSH on muscle mass independent of testosterone. These findings support tailored clinical assessment and management strategies in hypogonadal men with these genetic disorders.
References
Kama Study Authors 2025 -- Assessment of Body Composition via DXA in Individuals with Klinefelter and Kallmann Syndromes
