BRD2 and Kallmann syndrome: Univariable analysis revealed an inverse association between FSH levels and ALMI (B = -0.026; P = .002), which remained statistically significant after adjustment for confounders (B = -0.030; P = .0022).<h4>Conclusion</h4>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 T levels.