title: The assessment of bone health in young women with childhood-onset type one diabetes mellitus
Creators: name: Abdalrahaman, Naiemh
Publisher: name: University of Glasgow
Year: 2017

description: The risk of hip fracture in people with type one diabetes mellitus (T1DM) is reported to be 7 to 12 times greater than in those without T1DM, and this increased risk is evident in both children and young adults. This fracture risk is higher than expected bone mineral density (BMD) measurements, which indicates the likelihood that other skeletal factors, not captured by DXA, may contribute toward increased fracture risk. There is increasing evidence that alteration in trabecular bone microarchitecture and increased bone marrow adiposity (BMA) are causes for excess skeletal fragility, yet these data are lacking in people with T1DM. Recent technological advances in magnetic resonance imaging (MRI) have allowed the quantification of trabecular bone architecture. In addition, MRI can quantify the amount of intra-abdominal fat, and magnetic resonance spectroscopy (MRS) can also be used to assess BMA. These advances may enhance our understanding of the underlying causes of diabetic osteopathy which may lead to improved fracture risk predictors and preventive measures in patients with T1DM beyond that provided by dual energy x-ray absorptiometry (DXA). The overall objective of this thesis was to improve the understanding of the bone pathology of young adult women with childhood-onset T1DM by using high resolution MRI. A cross-sectional study was first carried out to assess trabecular bone microarchitecture of the tibia, vertebral BMA and abdominal adiposity in patients with childhood onset T1DM (n=30) compared with healthy controls (n=28). Additionally, the biochemical markers of bone turnover, adiposity and GH/IGF-1 axis (IGF-1, IGFBP3, and ALS) were examined to evaluate the underlying mechanism that might result in bone deficit in this group of people. We found that young women with childhood onset T1DM had reduced apparent trabecular bone volume (appBV/TV) and apparent trabecular number (appTbN) and greater apparent trabecular separation (appTbSp) than women without T1DM. Interestingly, these differences remained significant after adjustment for multiple confounders. Furthermore, these abnormalities were markedly obvious in those with microvascular complication compared with those without microvascular complication. Although women with T1DM had greater abdominal adiposity compared with healthy controls, there was no significant difference in BMA between the groups. However, BMA showed positive significant association with current glycaemic control (r= 0.45, p=0.02). Women with T1DM had lower bone turnover and decreased GH/IGF axis compared with healthy controls. Osteocalcin and ALS were negatively correlated with trabecular separation in women with T1DM. III Next, a one-year prospective study was conducted in a subset (n=28) of the participants involved in the cross-sectional study. The aim of this study was to compare one year changes in trabecular bone microarchitecture and BMA in women with and without T1DM. Additionally, the study aimed to evaluate the effect of glycaemic control on these changes over this period. After adjustment for relevant confounders, the cases (n=17) had a lower median appTbN and a higher median appTbSp at baseline and 12 months compared with healthy controls (n=11). Although the sample size was small at follow-up, the trabecular bone deficits were clearly noticeable in those with retinopathy compared with those without retinopathy. Similarly, there was no difference in median BMA which was 26.2% (12.1, 62.1) and 22.4% (9.6, 41.9) in cases and controls, respectively (p=0.57). Additionally, over the 12 month period, there was no significant change in MRI-measured parameters in cases or in controls, and no differences in the change of these variables between the two groups. Mixed model effect analysis showed that age was a negative predictor of percent changes of appBV/TV, appTbN and appTbSp in both cases and controls (p=0.02, p=0.02, p=0.002, respectively). Interestingly, there was a strong correlation between change in HbA1c and change in BMA (r=0.8; p=0.002). In the third study, we aimed to assess adiposity-based determinants of bone mineral density and bone microarchitecture in healthy young women and women with T1DM. Additionally, we aimed to compare the feasibility of using DXA and MRI-measured bone parameters to differentiate women with and without T1DM. In addition to high resolution MRI we used DXA scans to measure BMD and body composition from the same participants (n=26) involved in the longitudinal study. Vertebral BMA was positively correlated with VAT. Additionally, we demonstrated evidence of an inverse association of vertebral BMA and DXA-measured bone parameters of femoral neck, lumbar spine and total body independent of demographics and body composition in healthy young women and women with T1DM. These finding support the hypothesis that BMA is linked with low bone density, and may contribute to excess bone fragility. Moreover, this study suggested that MRI-measured trabecular bone measurements were able to differentiate between T1DM with and without microvascular complication compared with DXA-measured BMD. In summary, differences in MRI-measured trabecular microarchitecture parameters identified in this body of work provide preliminary explanations for elevated fracture risk in young women with childhood onset T1DM. Additionally, these findings provide potential insight into a number of possible underlying mechanisms of diabetic osteopathy.