Effects of projective bone area size of the spine on bone density and the diagnosis of osteoporosis in healthy pre-menopausal women in China

The genetic, environmental and phenotypic correlations of bone phenotypes at the spine and hip in Chinese

BACKGROUND

Bone mineral density (BMD), bone mineral content (BMC), and bone size have been widely studied individually as important risk factors for osteoporotic fracture, but little is known about the correlation and the degree of sharing genetic and environmental factors between the pairs of the three phenotypes.

AIM

The study investigated genetic correlation (rhoG), environmental correlation (rhoE) and phenotypic correlation (rhoP) between BMD, BMC and bone size.

SUBJECTS AND METHODS

Bivariate variance decomposition analyses were performed in 904 subjects from 287 Chinese nuclear families.

RESULTS

Significant rhoE, rhoG and rhoP were detected between BMD, BMC and bone size, except for rhoE between BMD and bone size at the hip (rhoE = 0.121, p = 0.361). Common shared genetic factors explained 86.1% and 60% of BMD and BMC genetic variations at the spine and hip, respectively. However, the genetic and environmental correlations between BMD and bone size were limited. rhoE and rhoG at the spine were 0.392 and 0.381, and at the hip were 0.121 and -0.205, respectively. Only 14.5% and 4.2% of variations between BMD and bone size at the spine and hip may be due to the shared genetic factors.

CONCLUSION

The obtained results suggested that bone size may be used as another surrogate phenotype independently of BMD for eventual elucidation of the pathogenesis of osteoporosis because of the limited correlations between BMD and bone size.

Race/ethnicity and fracture risk assessment: an issue that is more than skin deep

The study of race/ethnicity in relation to health outcomes and health disparities is of great importance in medicine. This is as true in the field of osteoporosis as it is in others, and it comes into sharp focus when the question of population-specific reference data for bone densitometry arises. Race/ethnicity can be viewed as both an ecosocial construct and as a biomedical concept. Whether or not, and how, to use race/ethnicity in fracture assessment potentially places these two paradigms in opposition. In this article, some of the issues that need to be considered to develop a rational approach to reference data selection and a globally acceptable measure of fracture risk are reviewed. Race/ethnicity is often a proxy for other disease-related risk factors. Understanding fundamental risk factors goes beyond the language of race/ethnicity.

Comparison of spine and femur reference data in native Chinese women from different regions of China

The aim of this study is to explore the differences of BMD reference curves at various skeletal sites among Chinese women from different regions of China and to investigate the feasibility of establishing a unified national BMD reference database for Chinese women. We measured BMD at the posteroanterior (PA) lumbar spine, femoral neck, trochanter and Ward's triangle by dual-energy X-ray absorptiometry bone densitometer in 3,422 Changsha women of South Central China, aged 20-84 years. The documented BMDs of reference populations of women in all other areas included Shanghai ( n =2,111) and Nanjing ( n =3,174) in the East, Shenyang ( n =1,213) in the Northeast, Kunming ( n =523) in the Southwest, Chongqing ( n =811) in the Midwest and Xian ( n =1,320) in the Northwest. We adopted the cubic regression as the fitting model for reference curves of BMD that varied with age, conducted conversions of BMD measured by various bone densitometers from different manufacturers and compared the differences between standardized BMD (sBMD) reference curves and combined ones for women from different areas. Our results revealed that by comparing variances in women from different areas, the average variances of non-standard BMD were 0.8-30.8% at the PA spine, 0.7-24.5% at the femoral neck, 0.6-29.9% at the trochanter and 1.1-54.7% at Ward's triangle, while average variances of sBMD either significantly decreased or disappeared (0.8-3.9% at the PA spine, 0.7-8.6% at the femoral neck, 0.6-8.3% at the trochanter and 1.1-29.9% at Ward's triangle). The sBMD reference curves were highly positive-dependent with combined ones ( r =0.913-0.999, P =0.000). At the PA spine and trochanter, the effect of combined sBMD curves presented well in women from different areas, except for those from Shanghai at the PA spine and Shenyang at the trochanter, indicating that sBMD curves were significantly different from pooled ones; at the femoral neck and Ward's triangle, the effect of combined sBMD reference curves was poor, indicating that sBMD curves demonstrated significant differences from pooled ones in women from a majority of these areas. We conclude that, in high density population areas, sBMD reference curves showed no significant geographic differences in women from various regions. In women from different areas, sBMD reference curves present good pooled results at the PA spine and trochanter. The less ideal combining effect of the sBMD curves at both femoral neck and Ward's triangle might be caused by the intrinsic differences from the different measuring instruments.

Relationship of body surface area with bone density and its risk of osteoporosis at various skeletal regions in women of mainland China

The aim of this study was to investigate the relationship between body surface area (BS) and bone mineral density (BMD) and the associated osteoporosis risk at various skeletal regions in women from mainland China. BMD was measured at the posteroanterior (PA) spine (L1-L4), supine lateral spine (L2-L4) including volumetric BMD (vBMD), hip including femoral neck, trochanter and total hip, and forearm, including radius + ulna ultradistal (R + UUD), 1/3 site (R + U1/3) and total region (R + UT) using a dual-energy X-ray absorptiometry (DXA) fan-beam bone densitometer (Hologic QDR 4500A) in 3418 females aged from 18 to 75 years. Data analysis revealed a positive correlation between BS and BMD at the various skeletal regions (r = 0.114-0.373, all P = 0.000), but no correlation with vBMD (r = 0.000, P = 0.934). Using the stepwise regression model, BMDs at various skeletal regions were dependent variables while height, weight, body mass index (BMI), BS and projective bone area (BA) were independent variables; BS was determined to be the most important variable that affected the PA spine, hip and forearm BMDs. Subjects were divided into three groups according to size: large BS group (LBSG), intermediate BS group (IBSG) and small BS group (SBSG). The BMD at different skeletal regions of subjects between groups exhibited a significant gradient difference, with LBSG > IBSG > SBSG, but this was not seen for vBMD. On the fitting curves where BMD varied with age at the PA spine, femoral neck, total hip and R + UUD, BMDs of LBSG were 6.93-9.29% higher than those of IBSG and 12.1-16.9 % higher than those of SBSG, whereas those of SBSG were 6.12-9.59% lower than those of IBSG at various skeletal regions, respectively. The prevalence rates and risks of osteoporosis of LBSG were significantly lower than those of SBSG and IBSG, whereas those of IBSG were obviously lower than those of SBSG at various skeletal regions, respectively, presenting a gradient difference among the three study groups, LBSG < IBSG < SBSG. Our study shows that the relationship between BS and BMD exceeds that between BMD and height or weight in women in mainland China. When areal BMD is employed, those with a larger BS have higher areal BMD and lower risks of osteoporosis while, conversely, those with a smaller BS have lower areal BMD, and therefore higher risk for osteoporosis. However, when vBMD is used, these differences diminish or even disappear.