Bone mass and mineral metabolism in Klinefelter's syndrome.

A reduced bone mineral density (BMD) is frequently observed in hypogonadal males; however, very little is known on bone and mineral metabolism in Klinefelter's syndrome (KS). In this study 32 XXY KS patients and 24 healthy age-matched male controls were examined. Serum total and free testosterone (TT and FT) were significantly lower in patients than in controls (TT in KS, 15.1 +/- 7.8 nmol/l; controls, 30.4 +/- 9.1; p < 0.001. FT in KS, 81.8 +/- 24.9 pmol/l; controls, 135.7 +/- 16.4; p < 0.001). 17 beta-Estradiol was slightly higher in KS patients (KS, 49.0 +/- 27.1 pg/ml; controls, 39.3 +/- 16.4 pg/ml), but the difference was not significant. BMD, measured at the spine (L2-4) and at the proximal epiphysis of the left femur, was similar in patients and in the control group (spine: KS, 1.016 +/- 0.142; controls, 1.085 +/- 0.144 g/cm2; p = not significant. Femoral neck: KS, 0.926 +/- 0.149; controls, 0.926 +/- 0.122 g/cm2; p = not significant). Bone GLA protein (BGP) was significantly higher in the KS group (12.7 +/- 4.8 vs 8.9 +/- 5.2 ng/ml; p < 0.02), while serum calcium, serum phosphate, calciotrophic hormones and the fasting urinary hydroxyproline/creatinine ratio (OHP/Creat) were similar in the two groups. A positive relationship between FT and both spine and femoral BMD was found in KS patients. Furthermore, OHP/Creat ratio was inversely related to BMD at the femur, and positively related to BGP in KS patients, but not in normal subjects. These findings suggest that (1) KS patients have normal bone mass, most probably because the hypogonadism is moderate; and (2) patients with lower bone mass appear to have higher bone turnover.