Endocrine Abstracts

Introductions: Gender Identity Disorder (GID) occurs when a person’s gender identity differs from their biological sex, causing distress (gender dysphoria). 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 have body composition measurements and annual bone density scans. Two related studies were undertaken 1) Comparison of body composition between bone densitometry (iDXA) vs TANITA measurements (51 children) and 2) Longitudinal changes in bone density and body composition (iDXA) in 26 adolescents who had been on GnRH analogues for a year.

Results: The baseline (Pre-GNRHa) study included 51 patients (18 male, 33 female) with a mean age of 16.2 years (range 14.8–17.9). The iDXA recorded 19.5% more body fat (mean 4.6 kg (2.9SD)) and 16.8% less lean mass (mean 7.3 kg (3.4SD) than the Tanita scales.

The longitudinal study included 26 patients (10 male, 16 female), with the repeat scans done at a mean of 1.1 years after commencing GnRH analogues. The difference in bone density scores between the Post and pre GnRHa scans was: LSBMD −0.64 (0.38 SD), BMAD -0.68 (0.83 SD), TBBMD -0.23 (0.46 SD), TBLH +0.03 (SD 0.52). Analysis was carried out according to biological sex. The BMI Z-score increased by a mean of 0.2. The fat mass increased by a mean of 5.1 kg (7.3 SD), the lean mass and the BMC decreased by 4.5 kg (6.6 SD) and 48.1 g (75.4 SD) 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 increase the BMI and fat mass and reduces lean mass and bone density values. The clinical significance of these short term changes remain to be determined and whether these can be mitigated by the initiation of cross sex hormones.