Poster P160 - Bone marrow composition: The effect of GAHT use in AFAB and AMAB transgender people

Introduction: Some studies have shown that gender affirming hormone therapy (GAHT) can be protective on bone. However, an increased frac-ture risk was shown in assigned male at birth (AMAB) individuals, but not in assigned female at birth (AFAB) people. Fracture rate associated with feminizing therapy is not yet fully known, but there are few studies that evaluated this parameter and assessed the alterations that could potentially lead to an increase in bone fragility. Indeed, GAHT could have an impact on bone microstructure and on its composition. Recent studies have shown how changes in bone composition and microstructure could have a crucial role in the pathophysiology of bone fragility regardless of bone mineral density (BMD) baseline values. These studies were performed in reference populations affected by different types of endocrinopathies, in particular in hypogonadic patients. The evaluation of the medullary composition highlighted a possible negative role played by the bone marrow adipose tissue (BMAT) on BMD. Since GAHT acts by inducing serum levels of estradiol and testosterone to fall within the individual’s gender identity reference range, it may affect mesenchymal stem cells by promoting their differentiation into adipocytes over osteoblasts, compromising osteogenesis. Aim: To evaluate a real (a) BMD by dual X-ray absorptiometry (DXA) and BMAT by proton magnetic resonance spectroscopy (1H-MRS) in AMAB and AFAB transgender before and during GAHT. Materials and Methods: Fourteen AFAB and nine AMAB (mean age24.1 ± 7.8 and 27.1 ± 11 years, respectively) were recruited. BMD and trabecular bone score (TBS) were measured by DXA at lumbar (L1–L4), femur and radius sites before (T0) and 12 months (T12) after GAHT. 1H-MRS was performed on L1–L4 to quantify BMAT. Results: AFAB subjects: at T0 and T12, the densitometric parameters were within the normal age reference range; no statistically significant differences T0 versus T12 were detected. AMAB Subjects: At T12, a statistically significant reduction in L1–L4 BMD (1.064 ± 0.152 T0 vs. 1.047 ± 0.110 T12, p < 0.05) and an increase in TBS versus T0 (1112 ± 636 T0 vs. 1234 ± 612 T12, p < 0.05) could be demonstrated. Comparing AMAB and AFAB, a statistically significant difference in femoral neck and in total femur BMD (p < 0.05) was observed at T12. At T0, AMAB had significantly higher fat content (FC%) values than AFAB in both individual lumbar vertebral and in the mean value. At T12, in AFAB group, the FC% values remained relatively stable without significant changes. In AMAB, a trend linked to the reduction of FC% L3 can be demonstrated. The correlation analysis highlighted a significant negative correlation linking the L1–L4(BMD and Z-score) values with FC% at T0 (p < 0.05). The correlation remained statistically significant at T12 between L1–L4 BMD and FC% of L3, L4, and L5 (p < 0.05). Conclusion: Since BMAT has been associated with reduced bone integrity and fragility fractures, the negative correlation between BMD and BMAT might play a role in bone microstructure and fractures risk.