OR05-5 Body Mass Index (BMI) as a Predictor of Bone Mineral Density (BMD) in Gender Diverse Youth

Abstract

Abstract Objective GnRH agonists (GnRHa), used to prevent development of undesired secondary sex characteristics for gender diverse youth (GDY), may impede pubertal bone mineral accrual increasing the risk for osteopenia/osteoporosis during adulthood. Based on findings of low bone mineral density (BMD) scores (relative to natal sex) prior to GnRHa [1], we hypothesized BMD might be associated with body mass index (BMI) in GDY.Method: To test our hypothesis, we reviewed medical records for 27 GDY; 16 were designated female at birth (DFAB) and 11 were designated male at birth (DMAB). Age at presentation, gender identity, ages at initiation of GnRHa and gender affirming hormone treatment (GAHT), duration of GnRHa treatment prior to GAHT initiation, auxologic parameters including BMI, and lumbar spine BMD obtained from GE lunar IDXa dual-energy X-ray absorptiometry (DEXA) were extracted. Lumbar spine BMD was used for statistical analysis. Statistical analysis was performed with Microsoft Excel Analysis ToolPak. A linear regression model was used to determine significance of BMI and GnRHa as predictors of BMD Z-score using a significance level of 0.05. Legal gender marker was used to determine BMD Z-scores. Results BMI ranged from 16.93 kg/m2 to 35.79 kg/m2 (5th to the 99th percentile). DEXA scan results were available for 27 GDY with age range 10-25 years; mean age (±SD) was 17±3 years. BMD of the lumbar spine was obtained from 0-61 months (mean 30 ± 21 months) following initiation of GnRHa. Length of GnRHa treatment prior to GAHT initiation ranged from 0-53 months (mean 14 ± 12 months).Individuals were at different stages of the gender affirmation process including 1) No medical treatments, 2) GnRH agonist only, 3) GAHT only, and 4) combined GnRH agonist and GAHT. Using a linear regression model, length of GnRHa therapy and length of GnRHa without GAHT were not significantly associated with lumbar spine BMD in our sample (p = 0.44 and 0.29, respectively). Using a linear regression model, BMI was a significant positive predictor of higher lumbar bone mineral density (p = 0.03). Conclusion Sex hormone exposure during adolescence and young adulthood is essential for bone health. While GnRH agonists lower endogenous sex hormone exposure, in our sample, lower BMD was not associated with total duration of GnRHa therapy or duration of GnRHa treatment prior to GAHT. Rather BMD was positively associated with BMI regardless of gender affirming medical therapies. Limitations include small sample size, retrospective design, and the use of legal gender marker for normative values. The next step will be larger, prospective studies to identify predictors of low BMD in GD youth. This information will guide future management regarding BMD monitoring.