Endocrine Abstracts

JOINT1891

Background: There is lack of data on the physical changes occurring in very young transgender people undergoing puberty suppression (PS) and gender-affirming hormone therapy (GAHT). This study aimed to investigate how body composition changes in terms of fat mass (FM) and lean mass (LM) according to birth-assigned sex and affirmed gender during PS and GAHT.

Methods: This retrospective study included data from 201 adolescents starting PS under 15yr at a national gender service (139 trans boys and 62 trans girls). Data from 127 of them who subsequently received GAHT were available. Height, weight, BMI, total LM and FM were collected using Tanita body composition analyser. Participants were divided into two groups: ‘in puberty’ (Tanner stage 2-3, or testicular volume <15ml) and ‘completing puberty’ (Tanner stage 4-5, or testicular volume >15ml) adolescents.

Results: Among ‘in puberty’ trans boys, total FM increased on PS (2.49 kg, 95% CI 1.66;3.33) similar to LM (2.41 kg, 95% CI 1.85;2.97). In contrast, with ‘completing puberty’ trans boys the increase of total FM (1.80 kg, 95% CI 1.21;2.39) was higher than total LM (0.97 kg, 95% CI 0.63;1.30). Looking at Z-scores, ‘in puberty’ trans boys showed increases in FM after 3 years of PS (from 0.70 to 1.2), and mean LM z-scores decreased in both ‘in puberty’ (from 0.98 to 0.5) and ‘completing puberty’ (from 1.16 to 0.80). During GAHT, ‘in puberty’ trans boys showed a greater increase of total LM (6.28 kg, 95% CI 3.54;9.02); body composition after 2 years was FM 27% and LM 73% (vs FM 30% and LM 70% at baseline). Mean FM z-scores at 2yr of GAHT in both groups decreased over baseline but remained higher in comparison with the identified gender. In contrast, ‘completing puberty’ trans girls showed a greater increase of total FM during PS (4.27 kg, 95% CI 1.50;7.03), whereas body composition only changed slightly during GAHT. However, mean FM z-scores at 2yr of GAHT in trans girls were in normal range (0.1) according to the affirmed gender.

Conclusions: Early hormonal intervention accelerates FM gain in both genders. GAHT masculinises body composition with gains in LM for trans boys, but aligns FM for trans girls with that for typical cisgender girls.