Bone Abstracts

Objectives: Gender Identity Disorder (GID) occurs when a person’s gender identity differs from their biological sex, causing distress. GID presenting in childhood can dissipate at puberty. If it persists, they may progress to physical interventions. This involves the use of a GnRH analogue (GnRHa) for one year followed by cross sex hormones.

Methods: As part of the clinical assessments, adolescents had body composition measurements and annual bone density scans. Two related studies were undertaken; 1) Cross sectional study to compare the body composition data between bone densitometry (iDXA) vs Tanita measurements (85 children) and 2) Longitudinal changes in iDXA bone density and body composition in 32 adolescents who had been on GnRH for a year.

Results: The cross-sectional pre-GnRHa study included 85 patients (30 male, 55 female) with a mean age of 16.2 years (range 14.4–17.9). The mean height, weight and BMI SDS were 0.0, 0.9 and +1.0 SDS respectively. The iDXA recorded 5.4% more body fat (mean 4.6 kg, S.D. 3.2) and 8.2% less lean mass (mean 7 kg, S.D. 3.5) than the Tanita scales. Following sub-analysis, the iDXA recorded 3.3 kg more body fat in females and 6.9 kg in males, with 5.5 kg and 9.6 kg less lean mass in females and males respectively. The longitudinal study included 32 patients (11 male, 21 female), with repeat scans done at a mean of 1.1 years after commencing GnRHa. The mean (S.D.) difference in bone density scores between the pre and post GnRHa scans was: LSBMD −0.66 (1.1), BMAD −0.68 (1.0), TBBMD −0.2 (1.0), TBLH +0.0 (1.1). The BMI Z-score increased by a mean of 0.1 SDS. The fat mass increased by a mean (S.D.) of 6.2% (8.0), lean mass and BMC decreased by 4.3% (7.9) increased by 0.4% (0.7) respectively.

Conclusions: The Tanita body composition scales underestimate the body fat and overestimate lean mass compared to the iDXA. In post-pubertal adolescents, GnRHa for one year increases the BMI marginally but increases fat mass and reduces lean mass and BMC. The clinical significance of these short term changes remains to be determined.

Disclosure: The authors declared no competing interests.