Measurement of Volumetric Bone Mineral Density Accurately Determines Degree of Lumbar Undermineralization in Children with Growth Hormone Deficiency

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Abstract
The effect of anthropometric variables and bone size on bone mineral density (BMD) was examined in 22 children with GK deficiency (GHD) aged 6.1-8.0 yr at diagnosis and in 40 sex- and chronological age-matched controls. In all patients and controls, bone mineral content (BMC), BMD(area) and BMD corrected for the apparent bone volume (BMD(volume)) were measured by dual-energy x-ray absorptiometry in the lumbar spine at L2-L4 level. In patients, BMD(area) was corrected for body height (BMD(height)), body mass index (BMD(BMI)), and bone age (BMD(BA)). Patients showed significantly reduced (P < 0.0001) BMC (males 11.55 +/- 0.71 g, females 10.13 +/- 1.48 g) and BMD(area) (males 0.502 +/- 0.033 g/cm(2), females 0.515 +/- 0.034 g/cm(2)) compared with controls (BMC: males 18.09 +/- 1.23 g, females 15.58 +/- 1.87 g; BMD(area): males 0.689 +/- 0.065 g/cm(2), females 0.685 +/- 0.059 g/cm(2)). In patients, BMD(height) (males 0.537 +/- 0.031 g/cm(2), females 0.548 +/- 0.032 g/cm(2)) and BMD(BMI) (males 0.641 +/- 0.028 g/cm(2), females 0.624 +/- 0.035 g/cm(2)) remained significantly lower (P < 0.02 to P < 0.0001) than BMD(area) of controls. BMD(BA) of patients was significantly reduced (-1.49 +/- 0.51 Z score, P < 0.0001) in comparison with bone age-matched controls (n = 35). BMD(volume) was significantly lower (P < 0.01 to P < 0.0005) in patients (males 0.268 +/- 0.006 g/cm(3) females 0.276 +/- 0.010 g/cm(3)) compared with chronological age-matched controls (males 0.283 +/- 0.013 g/cm(3), females 0.293 +/- 0.017 g/cm3). Mean bone volume of patients was affected to a greater extent than bone area (-2.36 +/- 0.49 Z score and -1.56 +/- 0.70 Z score, respectively). Bone area/bone volume ratio was significantly higher in patients than in chronological age-matched controls (0.53 +/- 0.02 and 0.42 +/- 0.08, P < 0.0001, respectively). Chronological age, body height, BMI, and bone age correlated significantly with BMD(area) (r(2) = 0.389-0.450, P < 0.002 to P < 0.001) but not with BMD(volume) (P = not significant). The results show that anthropometric variables and bone size affect lumbar BMC and BMD(area) in children with GHD. Reduced lumbar BMD(volume) indicates that apparent true bone density is decreased in children with GHD, suggesting a role of GH in bone mineralization

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