Changes in Bone Marrow Adipose Tissue in Transgender and Gender Non-Conforming Youth Undergoing Pubertal Suppression: A Pilot Study

Abstract

Pubertal suppression with gonadotropin-releasing hormone (GnRH) agonists in transgender and gender non-conforming (TGNC) youth may affect acquisition of peak bone mass. Bone marrow adipose tissue (BMAT) has an inverse relationship with bone mineral density (BMD). To evaluate the effect of pubertal suppression on BMAT, in this pilot study we prospectively studied TGNC youth undergoing pubertal suppression and cisgender control participants with similar pubertal status over a 12-month period. BMD was measured by dual-energy X-ray absorptiometry and peripheral quantitative computed tomography. Magnetic Resonance T1 relaxometry (T1-R) and spectroscopy (MRS) were performed to quantify BMAT at the distal femur. We compared the change in BMD, T1-R values, and MRS lipid indices between the two groups. Six TGNC (two assigned female and four assigned male at birth) and three female control participants (mean age 10.9 and 11.7 years, respectively) were enrolled. The mean lumbar spine BMD Z-score declined by 0.29 in the TGNC group, but increased by 0.48 in controls (between-group difference 0.77, 95% CI: 0.05, 1.45). Similar findings were observed with the change in trabecular volumetric BMD at the 3% tibia site (−4.1% in TGNC, +3.2% in controls, between-group difference 7.3%, 95% CI: 0.5%-14%). Distal femur T1 values declined (indicative of increased BMAT) by 7.9% in the TGNC group, but increased by 2.1% in controls (between-group difference 10%, 95% CI: −12.7%, 32.6%). Marrow lipid fraction by MRS increased by 8.4% in the TGNC group, but declined by 0.1% in controls (between-group difference 8.5%, 95% CI: −50.2%, 33.0%). In conclusion, we observed lower bone mass acquisition and greater increases in BMAT indices by MRI and MRS in TGNC youth after 12 months of GnRH agonists compared with control participants. Early changes in BMAT may underlie an alteration in bone mass acquisition with pubertal suppression, including alterations in mesenchymal stem cells within marrow.

1. Introduction

Transgender and gender non-conforming (TGNC) youth frequently experience gender dysphoria with the development of secondary sex characteristics that do not align with their gender identity.¹ Early pubertal suppression with gonadotropin-releasing hormone (GnRH) agonists allows TGNC youth more time to explore their identity before pursuing gender-affirming treatment and has been shown to improve mental health outcomes.^{2, 3} However, suppression of intrinsic sex steroids with GnRH agonists raises concern about the adverse effects on bone mass acquisition.⁴

Estrogen deficiency can alter bone marrow mesenchymal stem cells by promoting their differentiation into adipocytes over osteoblasts, compromising osteogenesis.⁵ Pubertal suppression with GnRH agonists may result in increased bone marrow adipose tissue (BMAT) similar to findings in other adolescent groups with a hypogonadal state.⁶ In this pilot study, we aimed to evaluate the effect of pubertal hormone suppression on BMAT as measured by magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS). In addition, we explored study feasibility and preliminary results to inform the design of larger future studies.

2. Patients and Methods

2.1. Participants

We prospectively studied 6 TGNC youth at initiation of GnRH agonist therapy and after 12 months, and 3 cisgender control participants over 12 months. Inclusion of TGNC participants required a diagnosis of gender dysphoria and being within 6 weeks of initiating a GnRH agonist therapy (injectable or implant). Both TGNC and control participants were included if they were in early puberty (breast Tanner stage II or testicular volume 4-8 mL) and between age 9-14 years. As part of their clinical care, TGNC participants who had 25-hydroxyvitamin D concentration <30 ng/mL were treated with vitamin D supplementation. Data obtained at baseline and 12-month visits included demographics, medical history, anthropometry (height, weight, BMI, pubertal status), and skeletal health indices by dual-energy x-ray absorptiometry (DXA), peripheral quantitative computed tomography (pQCT), MRI and MRS. This study protocol was approved by Cincinnati Children’s Hospital Medical Center (CCHMC) Institutional Board Review. Informed assent and consent were obtained from participants and their guardian at study enrollment.

2.2. Dual-energy X-ray Absorptiometry

Areal BMD (aBMD) of the total body less head (TBLH) and lumbar spine (LS) were measured using a Hologic Horizon DXA system. Height for age adjusted aBMD Z-scores (HAZ) were generated using pediatric reference data.⁷ LS bone mineral apparent density (BMAD) Z-scores were calculated to estimate volumetric BMD.^8,9

2.3. Peripheral Quantitative Computed Tomography

Volumetric BMD (vBMD) of the left tibia was measured at sites 3%, 38%, and 66% of tibial length using a Stratec XCT 2000 pQCT scanner (Orthometrix, White Plains, NY). We analyzed trabecular vBMD at site 3% and cortical vBMD at site 66% in this pilot study.

2.4. MRI and MRS Bone Marrow Adipose Tissue (BMAT) assessment

All participants underwent MRI of the left knee using a 3 Tesla MRI scanner (Philips Healthcare, Best, the Netherlands). Sagittal, three dimensional, proton-density weighted, fast spin-echo images were obtained through the knee with a field of view of 160 centimeter (cm) to include the distal femoral and proximal tibial metaphyses. We acquired coronal spin-lattice (T1) relaxometry consisting of seven fast-spin echo acquisitions of varying repetition time values (350 – 3000 milliseconds) with a field of view of 140 cm through the knee.

Single voxel point resolved spectra were acquired with the lateral aspect of the distal femoral metaphysis with a volume of 1 cm³ using the point resolved spectroscopy sequence (PRESS) localization technique for non-water suppressed spectra. Spectral post-processing was performed with JMRUI MRS processing software (www.jmrui.eu) to fit the water and methylene/methyl resonances, quantify peak areas and establish T2 corrected fat/(fat + water) ratios (extrapolated to echo time = 0 milliseconds).

We reported T1 relaxation (T1-R) values and fat fraction by MRS as markers for BMAT. BMAT has lower T1-R values relative to hematopoietic marrow, therefore, a decrease in T1-R values indicates increased BMAT and decreased hematopoietic marrow.

2.5. Statistical analysis

Due to the small sample size, no inferential analysis was conducted. Instead, we provided descriptive statistics and estimates of group differences with the corresponding 95% confidence interval. The estimated change (baseline to 12-month) in BMD, T1-R values and MRS lipid indices were compared between the two groups.

3. Results

3.1. Clinical characteristics

Descriptive data are summarized in Table 1. All participants were Tanner pubertal stage II at their baseline assessment. Pubertal stage for TGNC participants (who received GnRH agonists) remained unchanged at 12 months, whereas all control participants progressed to Tanner stage III.

Table 1.

Baseline characteristics of TGNC and control participants

	TGNC (N = 6)	Control (N = 3)	95% Confidence Interval
Sex assigned at birth
- male (n)	4	0
- female (n)	2	3
Age (years)	10.9 (10.2, 11.2)	11.7 (10.5, 12.9)	[−2.2, 0.6]
BMI Z-score	0.72 (−1.36, 2.29)	0.55 (0.09, 1.48)	[−2.26, 1.93]
aBMD by DXA
- LS aBMD HAZ	−0.10 (−0.66, 1.54)	−0.80 (−1.85, −0.18)	[−2.50, 0.31]
- TBLH aBMD HAZ	0.20 (−1.81, −0.35)	0.18 (−1.33, −0.89)	[−0.87, 0.64]
- LS BMAD Z-score	0.26 (−0.92, 1.91)	−1.12 (−1.77, −0.57)	[−2.84, 0.08]
vBMD by pQCT
- 3% tibia trabecular vBMD (g/cm3)	0.23 (0.20, 0.24)	0.20 (0.17, 0.22)	[−0.06, 0.01]
- 66% tibia cortical vBMD (g/cm3)	1.01 (0.97, 1.07)	1.04 (0.99, 1.09)	[−0.04, 0.10 ]
BMAT by MRI
- T1-R (mSec)	623 (556, 702)	641 (626, 654)	[−79, 115]
- Marrow fat fraction by MRS (%)	60.0 (47.9, 73.7)	58.4 (55.2, 63.8)	[−18, 15.4]

Data presented as mean [min, max] or number (n)

BMI = body mass index; LS = lumbar spines; aBMD = areal bone mineral density; HAZ = height for age adjusted BMD Z-score; BMAD = bone mineral apparent density; TBLH = total body less head; vBMD = volumetric bone mineral density; pQCT = peripheral quantitative computed tomography; BMAT = bone marrow adipose tissue; MRI = magnetic resonance imaging; MRS = magnetic resonance spectroscopy

3.2. Bone mineral density by DXA and pQCT

Mean LS aBMD HAZ, TBLH aBMD HAZ, LS BMAD Z-score and trabecular vBMD (3% tibia) declined in TGNC participants while increasing in the control group (Figure 1 and 2). In contrast, cortical vBMD (66% tibia) appeared to increase in TGNC group.

Figure 1.

Mean changes in height for age adjusted aBMD Z-scores (HAZ) and bone mineral apparent density (BMAD) Z-scores over 12 months in control and TGNC participants. Lumbar spine (LS) aBMD HAZ: +0.48 vs. −0.29 (between-group difference of 0.77 with 95% CI: +0.05, +1.45) (1A). Total body less head (TBLH) aBMD HAZ: −0.06 vs. −0.46 (between-group difference of 0.40 with 95% CI: −0.21, +1.01) (1B). LS BMAD Z-scores: +0.80 vs. −0.20 (between-group difference of 1.0 with 95% CI: +0.09, +1.93) (1C).

Figure 2.

The change in trabecular vBMD at 3% tibia site by pQCT was +3.2% and −4.1% in the control and TGNC group, respectively (between group difference of 7.3% with 95% CI: +0.5%, +14.0%) (2A). The change in cortical vBMD at 66% tibia site was −1.2% and +1.0% in the control and TGNC group (n = 5), respectively (between group difference of −2.2 with 95% CI: −5.6%, +1.2%) (2B).

3.3. Bone marrow adipose tissue by MRI

T1-R values appeared to decline (indicative of increased BMAT) and MRS fat fraction increased more in the TGNC group (Figure 3). There appeared to be a linear relationship between the changes in trabecular vBMD and marrow lipid fraction by MRS.

Figure 3.

Distal femur T1 values declined (indicative of increased BMAT) by 7.9% in the TGNC group, in contrast to the 2.1% increase observed in controls (between-group difference of 10.0% with 95% CI: −12.7%, +32.6%) (3A). Marrow lipid fraction by MRS (n = 4) increased by 8.4% in the transgender group, but declined by 0.1% in controls (between-group difference of 8.5% with 95% CI: −50.2%, +33.0%) (3B). Relationship between changes in trabecular vBMD and marrow fat fraction by MRS is shown figure 3C.

4. Discussion

Adolescence is a critical period for bone mineral accrual. The suppression of pubertal hormones with GnRH agonists in TGNC youth has been associated with compromised BMD.⁴ In line with previous studies, we found a smaller gain in aBMD resulting in declining aBMD HAZ in TGNC youth receiving GnRH agonist therapy compared with control participants. We observed similar findings when BMD was adjusted for bone size. Interestingly, while there was a decline in trabecular vBMD by pQCT, GnRH agonists did not appear to compromise cortical vBMD. This observation may reflect preferential effects of sex steroids on trabecular bone.

There has been a growing understanding of the interactions between BMAT and BMD. To our knowledge, no other studies have evaluated the changes in BMAT following the suppression of pubertal hormones in TGNC youth. Using our previous published BMAT assessment protocol,⁶ we assessed the changes in BMAT indices at the distal femur by MRI and MRS at 12 months of pubertal hormone suppression. We observed a trend of greater increases in BMAT in TGNC participants compared with controls. In addition, there appeared to be an inverse trend between BMAT and BMD in both groups combined, similar to previous studies in healthy children and adults.^{10, 11} Sex steroids are known to play an important role in the development of BMAT.⁵ Estrogens and androgens (indirectly, via its aromatization) promote osteoblastogenesis and inhibit adipogenesis within marrow.^{5, 12} The lack of bone accrual accompanying increased BMAT in our study potentially reflects negative effects on bone formation as marrow changes occur with sex steroid suppression.

Although the small number of participants in our study limits the ability to draw definitive conclusions, these data provide insights into bone health in TGNC youth and suggest the potential of BMAT to serve as a biomarker in adolescents. Prospective studies applying a similar study protocol with larger numbers of participants and longer follow-up periods are needed to confirm our findings. Another study limitation is the lack of vitamin D assessment in the control group. If present, vitamin D deficiency in control participants could have lessened the group differences we observed.

In conclusion, data from our pilot study provide evidence of increasing BMAT after initiation of GnRH agonists, accompanied by declines in BMD. Early changes in BMAT may underlie an alteration in bone mass acquisition with pubertal suppression, including alterations in mesenchymal stem cells within marrow.