Bone mineral density and body composition in adolescents with Klinefelter Syndrome: accounting for tall stature

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Background: Hypogonadism and reduced lean body mass (LBM) increase risk for low bone mineral density (BMD) in men with X chromosome aneuploidies, including Klinefelter syndrome (KS). Despite peak bone mass accrual occurring during adolescence, pediatric studies in this population are limited. Moreover, interpretation of BMD by dual x-ray absorptiometry (DXA) is complicated as it converts a 2-dimensional measure to an "areal" bone mineral density (aBMD) and can overstate aBMD in youth with tall stature, a common feature of males with X chromosome aneuploidies. This study examined the differences between age-only and height-adjusted DXA measures, and relationships to body composition.   

Objective: To assess bone mineral density in relation to height and body composition in adolescents with Klinefelter syndrome.

Methods: Retrospective analysis of available lumbar spine (LS) aBMD and total body less head (TBLH) bone mineral content (BMC) by DXA (Hologic, Horizon) in males ages 9-19 years with X chromosome aneuploidies followed by our program. We calculated Z-scores for age-only adjusted and age- & height-for-age Z-score (HAZ)‒adjusted LS aBMD (LS-aBMD-Z and LS-aBMDHAZ-Z and TBLH-BMC-Z and TBLH-BMCHAZ-Z).  Z scores for bone mineral apparent density (BMAD), another way to account for height, was calculated. Z-scores for indices for LBM (LBMI-Z) and fat mass (FMI-Z) were also calculated. Statistics methods included descriptive, regression, and paired t test.

Results (mean+/-SD): 17 boys (14: 47XXY, 2: 48XXYY and 1: 49XXXXY), mean age 14.5 + 0.4 y (min-max: 9-19) with height-z (1.1 + 0.35), weight-z (0.75 + 0.3), and BMI-Z (0.15 + 0.4) were included. All were pubertal; 3 were on testosterone therapy. LS aBMD-Z values were lower when adjusted for Ht-Z: LS aBMD-Z =0.0012 + 0.3 versus LS aBMDHAZ -Z=-0.59 + 0.2, p=0.0016. We found similar results for total body measures: TBLH BMC-Z=-0.67 + 0.45 versus TBLH BMCHAZ -Z=-1.42 + 0.3, p= 0.02. LS BMADz = 0.29+ 0.27, which was not different than LS BMDz (p = 0.8). LBMI-z was -1.43 + 0.27. FMI-Z was normal at 0.56 + 0.2. LBMI-z correlated with LS BMADz, LS aBMDHAZ, and TBLH BMCHAZ, (p < 0.03), while FMI z was not associated with these DXA measurements (p >0.08).

Conclusions: Lumbar spine and TBLH BMC and BMD values are lower in adolescent boys with KS and other X chromosome aneuploidies when adjusted for height using the HAZ method but not with the BMAD method. This study emphasizes the importance of looking at height in relation to these parameters and questions the ideal method to account for height in this population. Lean mass was uniformly low in this cohort and correlated with bone mass, while fat mass was within normal range for age and not a predictor of bone mass. Future directions of this study include changes in bone and lean mass with early testosterone therapy.

CHOP/University of Pennsylvania Perelman School of Medicine

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