Genetic determinants of bone mineral content at the spine and radius: a twin study

Distinct Subsets of Noncoding RNAs Are Strongly Associated With BMD and Fracture, Studied in Weight-Bearing and Non-Weight-Bearing Human Bone

We investigated mechanisms resulting in low bone mineral density (BMD) and susceptibility to fracture by comparing noncoding RNAs (ncRNAs) in biopsies of non-weight-bearing (NWB) iliac (n = 84) and weight bearing (WB) femoral (n = 18) postmenopausal bone across BMDs varying from normal (T-score > -1.0) to osteoporotic (T-score ≤ -2.5). Global bone ncRNA concentrations were determined by PCR and microchip analyses. Association with BMD or fracture, adjusted by age and body mass index, were calculated using linear and logistic regression and least absolute shrinkage and selection operator (Lasso) analysis. At 10% false discovery rate (FDR), 75 iliac bone ncRNAs and 94 femoral bone ncRNAs were associated with total hip BMD. Eight of the ncRNAs were common for the two sites, but five of them (miR-484, miR-328-3p, miR-27a-5p, miR-28-3p, and miR-409-3p) correlated positively to BMD in femoral bone, but negatively in iliac bone. Of predicted pathways recognized in bone metabolism, ECM-receptor interaction and proteoglycans in cancer emerged at both sites, whereas fatty acid metabolism and focal adhesion were only identified in iliac bone. Lasso analysis and cross-validations identified sets of nine bone ncRNAs correlating strongly with adjusted total hip BMD in both femoral and iliac bone. Twenty-eight iliac ncRNAs were associated with risk of fracture (FDR < 0.1). The small nucleolar RNAs, RNU44 and RNU48, have a function in stabilization of ribosomal RNAs (rRNAs), and their association with fracture and BMD suggest that aberrant processing of rRNAs may be involved in development of osteoporosis. Cis-eQTL (expressed quantitative trait loci) analysis of the iliac bone biopsies identified two loci associated with microRNAs (miRNAs), one previously identified in a heel-BMD genomewide association study (GWAS). In this comprehensive investigation of the skeletal genetic background in postmenopausal women, we identified functional bone ncRNAs associated to fracture and BMD, representing distinct subsets in WB and NWB skeletal sites. © 2020 The Authors. Journal of Bone and Mineral Research published by American Society for Bone and Mineral Research.

Fracture risk factors among children living in New Zealand

Factures are common during childhood. There are limited data available regarding relationships between bone fracture history and calcium intake, sugar sweetened beverages (SSBs) intake, vitamin D status, physical activity (PA), ethnicity, and body composition in New Zealand (NZ) children. Identifying groups of NZ children at risk of fracture and associated predictors may help to improve bone quality during childhood and decrease the risk of fractures throughout life. The aim of this study was to investigate fracture history and associated risk factors in New Zealand children. Children aged 8-12 years were recruited. Capillary blood spots collected from a finger prick were as analyzed for 25(OH)D concentrations. Bioelectrical impedance analysis (InBody720, Seoul, Korea) was used to measure body fat percentage (%BF). Information about fracture history, siblings' history of fractures, family osteoporosis history, PA, ethnicity, and intake of calcium containing foods, and SSBs was collected using questionnaires. Children (n = 647, 354 girls), mean ± SD age 9.8 ± 0.7 years were recruited from six Auckland primary schools. NZ European (n = 252) (NZE) and South Asian (n = 68) children reported the lowest (20.2 %) and highest (44.1 %) fracture incidence, respectively. NZE compared to South Asian children, had higher 25(OH)D concentrations (74.6 ± 19.8 vs. 48.4 ± 19.3 nmol/L, P < 0.001), higher total calcium intake (764.0 ± 394.4 vs. 592.7 ± 266.3 mg/d, P < 0.018), and lower %BF (19.5 ± 6.6 vs. 23.4 ± 8.4, P < 0.003). Māori children had the next highest fracture rate (32.5 %). This group had adequate 25(OH)D (64.2 ± 18.9 nmol/L), but high %BF (23.9 %) and most participated in vigorous PA. After stratifying by sex, binary logistic regression analysis revealed the main determinants of fracture history for boys were high %BF, low 25(OH)D, low calcium intake, high SSBs consumption, siblings' fracture history, family osteoporosis history, and being South Asian; and in girls, high SSBs consumption, siblings' fracture history, and family osteoporosis history. We found South Asian ethnicity was a significant risk factor for boys. Some children were at high risk of vitamin D deficiency and for whom supplementation may be necessary in winter. Good nutrition (especially good sources of calcium and reducing SSBs intakes) should be recommended to children during growth and development to reduce their risk of fractures.

Trabecular architecture of the great ape and human femoral head

Studies of femoral trabecular structure have shown that the orientation and volume of bone are associated with variation in loading and could be informative about individual joint positioning during locomotion. In this study, we analyse for the first time trabecular bone patterns throughout the femoral head using a whole-epiphysis approach to investigate how potential trabecular variation in humans and great apes relates to differences in locomotor modes. Trabecular architecture was analysed using microCT scans of Pan troglodytes (n = 20), Gorilla gorilla (n = 14), Pongo sp. (n = 5) and Homo sapiens (n = 12) in medtool 4.1. Our results revealed differences in bone volume fraction (BV/TV) distribution patterns, as well as overall trabecular parameters of the femoral head between great apes and humans. Pan and Gorilla showed two regions of high BV/TV in the femoral head, consistent with hip posture and loading during two discrete locomotor modes: knuckle-walking and climbing. Most Pongo specimens also displayed two regions of high BV/TV, but these regions were less discrete and there was more variability across the sample. In contrast, Homo showed only one main region of high BV/TV in the femoral head and had the lowest BV/TV, as well as the most anisotropic trabeculae. The Homo trabecular structure is consistent with stereotypical loading with a more extended hip compared with great apes, which is characteristic of modern human bipedalism. Our results suggest that holistic evaluations of femoral head trabecular architecture can reveal previously undetected patterns linked to locomotor behaviour in extant apes and can provide further insight into hip joint loading in fossil hominins and other primates.

Trabecular bone patterning in the hominoid distal femur

BACKGROUND

In addition to external bone shape and cortical bone thickness and distribution, the distribution and orientation of internal trabecular bone across individuals and species has yielded important functional information on how bone adapts in response to load. In particular, trabecular bone analysis has played a key role in studies of human and nonhuman primate locomotion and has shown that species with different locomotor repertoires display distinct trabecular architecture in various regions of the skeleton. In this study, we analyse trabecular structure throughout the distal femur of extant hominoids and test for differences due to locomotor loading regime.

METHODS

Micro-computed tomography scans of Homo sapiens (n = 11), Pan troglodytes (n = 18), Gorilla gorilla (n = 14) and Pongo sp. (n = 7) were used to investigate trabecular structure throughout the distal epiphysis of the femur. We predicted that bone volume fraction (BV/TV) in the medial and lateral condyles in Homo would be distally concentrated and more anisotropic due to a habitual extended knee posture at the point of peak ground reaction force during bipedal locomotion, whereas great apes would show more posteriorly concentrated BV/TV and greater isotropy due to a flexed knee posture and more variable hindlimb use during locomotion.

RESULTS

Results indicate some significant differences between taxa, with the most prominent being higher BV/TV in the posterosuperior region of the condyles in Pan and higher BV/TV and anisotropy in the posteroinferior region in Homo. Furthermore, trabecular number, spacing and thickness differ significantly, mainly separating Gorilla from the other apes.

DISCUSSION

The trabecular architecture of the distal femur holds a functional signal linked to habitual behaviour; however, there was more similarity across taxa and greater intraspecific variability than expected. Specifically, there was a large degree of overlap in trabecular structure across the sample, and Homo was not as distinct as predicted. Nonetheless, this study offers a comparative sample of trabecular structure in the hominoid distal femur and can contribute to future studies of locomotion in extinct taxa.

The Impact of Test Outcome Certainty on Interest in Genetic Testing Among College Women

Osteoporosis and hemochromatosis are both late-onset preventable diseases, but future genetic tests for these conditions are likely to differ in their predictive abilities. To determine whether interest in a specific genetic test for hemochromatosis would be higher than interest in a theoretical test for osteoporosis susceptibility, undergraduate women at the University of Cincinnati (N = 181) were surveyed regarding their interest in genetic testing for these conditions. The clinical features of the diseases and the limits of a genetic test for each were described. Sixty-three percent of the total population was interested in genetic testing with a trend toward higher interest in the osteoporosis group. Disease familiarity, perceived disease severity, and perceived risk for disease appear to be more important predictors of genetic test acceptance than diagnostic specificity. Suggested implications for the development of population genetic screening tests are discussed.

Attenuated monocyte apoptosis, a new mechanism for osteoporosis suggested by a transcriptome-wide expression study of monocytes

BACKGROUND

Osteoporosis is caused by excessive bone resorption (by osteoclasts) over bone formation (by osteoblasts). Monocytes are important to osteoporosis by serving as progenitors of osteoclasts and produce cytokines for osteoclastogenesis.

AIM

To identify osteoporosis-related genes, we performed microarray analyses of monocytes using Affymetrix 1.0 ST arrays in 42 (including 16 pre- and 26 postmenopausal) high hip BMD (bone mineral density) vs. 31 (including 15 pre- and 16 postmenopausal) low hip BMD Caucasian female subjects. Here, high vs. low BMD is defined as belonging to top vs. bottom 30% of BMD values in population.

METHOD

Differential gene expression analysis in high vs. low BMD subjects was conducted in the total cohort as well as pre- and post-menopausal subjects. Focusing on the top differentially expressed genes identified in the total, the pre- and the postmenopausal subjects (with a p <5E-03), we performed replication of the findings in 3 independent datasets of microarray analyses of monocytes (total N = 125).

RESULTS

We identified (in the 73 subjects) and successfully replicated in all the 3 independent datasets 2 genes, DAXX and PLK3. Interestingly, both genes are apoptosis induction genes and both down-regulated in the low BMD subjects. Moreover, using the top 200 genes identified in the meta-analysis across all of the 4 microarray datasets, GO term enrichment analysis identified a number of terms related to induction of apoptosis, for which the majority of component genes are also down-regulated in the low BMD subjects. Overall, our result may suggest that there might be a decreased apoptosis activity of monocytes in the low BMD subjects.

CONCLUSION

Our study for the first time suggested a decreased apoptosis rate (hence an increased survival) of monocytes, an important osteoclastogenic cell, as a novel mechanism for osteoporosis.

A trabecular plate-like phenotype is overrepresented in Chinese-American versus Caucasian women

This study used extreme phenotype selection to define two trabecular bone phenotypes in a cohort of Chinese-American and Caucasian women. A trabecular plate-predominant phenotype is more common in Chinese-Americans while the rod-predominant phenotype is more typical of Caucasians. The robustness of these phenotypic associations with respect to lifestyle factors suggests that this trait may have a genetic basis and that these phenotypes can be utilized in future genetic studies.

INTRODUCTION

Compared to Caucasians, Chinese-Americans have more plate-like trabecular bone when measured by individual trabecula segmentation (ITS). These findings suggest a phenotypic difference between the races, which may be amenable to genetic analysis. We sought to identify a single ITS plate trait to pursue in genetic studies by conducting an extreme phenotype selection strategy to numerically define two distinct phenotypes-plate-like and rod-like-and determine whether the selected phenotypic associations were independent of lifestyle factors in order to conduct future genetic studies.

METHODS

A previously described cohort of 146 Chinese-American and Caucasian women with high-resolution peripheral quantitative computed tomography imaging and ITS analyses were studied with logistic regression and receiver operator characteristic analyses.

RESULTS

The tibial plate-to-rod (TPR) ratio was the best ITS discriminator of race. Using extreme phenotypic selection, two TPR ratio phenotypes were defined numerically: plate-like as a TPR ratio value in the highest quartile (≥1.336) and rod-like as a TPR ratio value in the lowest quartile (≤0.621). Women with a plate-like phenotype were 25.7 times more likely (95 % CI 7.3-90.1) to be Chinese-American than women with rod-like morphology. After controlling for constitutional and lifestyle covariates, women in the highest vs. lowest TPR ratio quartile were 85.0 times more likely (95 % CI 12.7-568.0) to be Chinese-American.

CONCLUSION

Using extreme phenotype selection, we defined a plate- and rod-like trabecular bone phenotype for the TPR ratio trait. The former phenotype is more common in Chinese-American women, while the latter is more typical of Caucasian women. The robustness of these phenotypic associations after controlling for differences in constitution and lifestyle suggest that the TPR ratio may have a genetic basis and that the extreme phenotypes defined in this analysis can be utilized for future studies.

Pubertal timing, bone acquisition, and risk of fracture throughout life

Pubertal maturation plays a fundamental role in bone acquisition. In retrospective epidemiological surveys in pre- and postmenopausal women, relatively later menarcheal age was associated with low bone mineral mass and increased risk of osteoporotic fracture. This association was usually ascribed to shorter time exposure to estrogen from the onset of pubertal maturation to peak bone mass attainment. Recent prospective studies in healthy children and adolescents do not corroborate the limited estrogen exposure hypothesis. In prepubertal girls who will experience later menarche, a reduced bone mineral density was observed before the onset of pubertal maturation, with no further accumulated deficit until peak bone mass attainment. In young adulthood, later menarche is associated with impaired microstructural bone components and reduced mechanical resistance. This intrinsic bone deficit can explain the fact that later menarche increases fracture risk during childhood and adolescence. In healthy individuals, both pubertal timing and bone development share several similar characteristics including wide physiological variability and strong effect of heritable factors but moderate influence of environmental determinants such as nutrition and physical activity. Several conditions modify pubertal timing and bone acquisition, a certain number of them acting in concert on both traits. Taken together, these facts should prompt the search for common genetic regulators of pubertal timing and bone acquisition. It should also open epigenetic investigation avenues to pinpoint which environmental exposure in fetal and infancy life, such as vitamin D, calcium, and/or protein supplies, influences both pubertal timing and bone acquisition.

Bone Mineral Density in Children From Anthropological and Clinical Sciences: A Review

Bone mineral density (BMD) is a frequent topic of discussion in the clinical literature in relation to the bone health of both adults and children. However, in archaeological and/ or anthropological studies the role of BMD is often cited as a possible factor in the poor skeletal preservation which can lead to an under-representation of juvenile skeletal remains. During skeletal development and growth throughout childhood and adolescence changes take place in both the size and shape of bones and these changes also result in the increasing of mineral content. BMD can be affected by many factors, which include, age, genetics, sexual maturation, amount of physical activity and dietary calcium. This paper aims to review the clinical and anthropological literature on BMD and discuss the numerous methods of measurement and how the availability of certain methods such as Dual-energy x-ray absorptiometry (DEXA) and quantitative computed tomography (QCT) can influence the study of bone density in archaeological skeletal collections and also the future potential for forensic anthropological studies.

Association of GALNT3 gene polymorphisms with bone mineral density in Chinese postmenopausal women: the Peking Vertebral Fracture study

OBJECTIVE

GALNT3 gene encodes the glycosyltransferase polypeptide N-acetylgalactosaminyltransferase-3 (ppGalNacT3), which initiates the O-glycosylation of fibroblast growth factor 23 (FGF23) that is important in phosphorous regulation. Inactivating mutations of the GALNT3 gene can cause familial tumoral calcinosis. The aim of present study is to investigate the association of GALNT3 polymorphisms with osteoporosis phenotypes in Chinese postmenopausal women.

METHODS

A community-based population of 1,353 postmenopausal women was randomly selected in Beijing. Bone mineral densities (BMDs) of the lumbar spine, femoral neck (FN), and total hip (TH) were measured by dual-energy x-ray absorptiometry. Vertebral fracture phenotypes were ascertained by vertebral x-ray reading. Osteoporotic fracture phenotypes were obtained from questionnaires. Single nucleotide polymorphisms of GALNT3 were determined by TaqMan allelic discrimination assay. Differences in BMD, serum phosphorus, or serum calcium across diverse genotypes or haplotypes were analyzed by general linear model analysis of covariance. Linear regression or logistic regression was used for association analyses of different osteoporosis phenotypes, phosphorous, or calcium. Partial correlation was used to investigate the relationship between phosphorus or calcium and BMD.

RESULTS

We found that polymorphisms of rs1863196, rs6710518, and rs13429321 were significantly associated with FN BMD (P values of 0.002, 0.003, and 0.002, respectively). Polymorphisms of rs1863196, rs6710518, rs4667492, rs13429321, and rs6721582 were associated with TH BMD (P values of 0.002, 0.004, 0.037, 0.005, and 0.014, respectively). Haplotype-1 additive and dominant models were found to be associated with TH BMD (P values of 0.035 and 0.024, respectively). Haplotype-2 dominant model was found to be associated with FN BMD (P = 0.003) and TH BMD (P = 0.001).

CONCLUSIONS

GALNT3 may play a role in genetic susceptibility to osteoporosis among Chinese postmenopausal women. Efforts should be exerted to replicate our findings in other similar and ethnically diverse populations.

Genetic influence on bone phenotypes and body composition: a Swedish twin study

Bone mineral density (BMD), bone size and bone turnover are independent determinants of fractures in elderly. Earlier twin studies of these phenotypes have revealed high heritability for BMD and bone area, and more moderate heritability for bone turnover markers. No previous Scandinavian study has evaluated the genetic and environmental contribution to the variance of these phenotypes, despite the fact that Scandinavian countries have the highest incidence of osteoporotic fractures worldwide. Participants were selected from the Swedish Twin Registry. All intact like-sexed twin pairs born in 1965 or earlier and living in the county of Uppsala were invited to participate. A total of 102 twin pairs (45 monozygotic and 57 dizygotic) accepted the invitation to participate. All twins underwent measurement of BMD and bone area using dual-energy X-ray absorptiometry. Hip geometry was also calculated. Markers for bone formation (osteocalcin) and bone resorption (CrossLaps) were measured in serum. We observed a substantial heritability for BMD at the lumbar spine (0.85; 95 % CI 0.54-0.90), the femoral neck (0.75; 95 % CI 0.62-0.83), and the proximal femur (0.84; 95 % CI 0.74-0.90). The values for bone area were approximately similar to those for BMD. Bone turnover markers had a slightly lower genetic influence with a value of 0.69 (0.53-0.80) for osteocalcin and 0.58 (95 % CI 0.33-0.75) for CrossLaps. As a comparison, the heritabilities of body height and weight were 0.95 and 0.82, respectively. The high heritability on bone phenotypes among Swedish middle-aged and older men and women should encourage further work on the identification of specific genetic pathways. Continuing research in this area could reveal the mechanisms behind the strong genetic susceptibility of bone-related phenotypes.

Impaired trabecular and cortical microarchitecture in daughters of women with osteoporotic fracture: the MODAM study

We investigated the familial resemblance of bone microarchitecture parameters between postmenopausal mothers with fragility fracture and their premenopausal daughters using high-resolution peripheral quantitative computed tomography (HR-pQCT). We found that daughters of women with fracture have lower total volumetric bone mineral density (vBMD), thinner cortices, and impaired trabecular microarchitecture at the distal radius and tibia, compared to controls.

INTRODUCTION

Familial resemblance of areal bone mineral density (aBMD) in mothers and daughters has been widely studied, but not its morphological basis, including microarchitecture.

METHODS

We compared aBMD, vBMD, bone size, and bone microarchitecture at the distal radius and tibia assessed by HR-pQCT in mothers and their premenopausal daughters. We included 115 women aged 43 ± 8 years whose mothers had sustained a fragility fracture and 206 women aged 39 ± 9 years whose mothers had never sustained a fragility fracture.

RESULTS

Women whose mothers had fracture had significantly (p < 0.05) lower aBMD at the lumbar spine, total hip, femoral neck, mid-distal radius, and ultradistal radius compared to controls. In similar multivariable models, women whose mothers had a fracture had lower total vBMD at the distal radius (-5 %, 0.3 standard deviation [SD]; p < 0.005) and distal tibia (-7 %, 0.4 SD; p < 0.005). They also had lower cortical thickness and area at the distal radius (-5 %, 0.3 SD and -4 %, 0.2 SD, respectively; p < 0.005) and at the distal tibia (-6 %, 0.3 SD and -4 %, 0.3SD, respectively; p < 0.005). Trabecular vBMD was lower at the distal radius (-5 %, 0.3 SD; p < 0.05) and tibia (-8 %, 0.4 SD; p < 0.005), with a more spaced and heterogeneous trabecular network (4 and 7 % at the radius and 5 and 9 %, at the tibia, p < 0.05, for Tb.Sp and Tb.Sp.SD, respectively).

CONCLUSION

Premenopausal daughters of women who had sustained fragility fracture have lower total and trabecular vBMD, thinner cortices, as well as impaired trabecular microarchitecture at the distal radius and tibia, compared with premenopausal daughters of women without fracture.

Gender differences in the heritability of musculoskeletal and body composition parameters in mother-daughter and mother-son pairs

Bone mass and body composition traits are genetically programmed, but the timing and gender and site specificities of their heritability are unclear. Mother-child correlations of bone mineral density (BMD) and bone mineral content, lean mass, and fat mass were studied in 169 premenopausal mothers and their 239 children. Heritability estimates of lean mass, fat mass, BMD, and area were derived for each gender and pubertal stage. There were significant correlations for most densitometry-derived variables at the spine, hip, femoral neck (FN), and total body (r=0.192-0.388) in mother-postmenarcheal daughter pairs, for bone areas at all sites in early puberty (r=0.229-0.508) and for volumetric-derived density at FN and spine (r=0.238-0.368) in mother-son pairs. Fat mass correlations were significant in both genders after puberty (r=0.299-0.324) and lean mass in postmenarcheal girls only (r = 0.299). Heritability estimates varied between 21% and 37% for mother-daughter and 18% and 35% for mother-son pairs for density-derived variables and between 26% and 40% for body composition variables. Maternal inheritance of bone traits is expressed in early-pubertal boys for several skeletal site traits but consistently involves most site traits in girls and boys by late puberty. Body composition inheritance is more variable.

Bone Mineral Changes and Cardiovascular Effects among Female Athletes with Chronic Menstrual Dysfunction

Purpose

Oligo/amenorrhea, as a part of the Female Athlete Triad has adverse effects on the athlete's bone mineral density (BMD) and cardiovascular system. Hypoestrogenism, due to suppression of hypothalamus-pituitary axis (HPA) as a result of energy imbalance, is the possible cause of the Triad. This study was designed based on following up and reassessment of elite female athletes who were diagnosed as menstrual dysfunction about two years ago.

Methods

This study was conducted in three phase sections: 1) Reassess the pattern of menstrual cycle among athletes who reported menstrual dysfunction about two years ago; 2) Bone mineral density was measured twice in the same machine and same center with a two-year interval; 3) The laboratory data including blood glucose, lipid profile and inflammatory markers was assessed in phase 3.

Results

BMD of athletes did not change significantly after 25.5 months of oligomenorrhea P (spine) = 0.2, P (femur)=0.9. Mean of all cardiovascular factors was in the normal range except for high density lipoprotein (HDL) which was 49.28 (SD=9.18), however, most of the athletes had abnormalities in their lipid profile. Inverse relationship between the increase in the BMD of spine and total cholesterol (r =−0.49, P=0.04), Apolipoprotein A (r = −0.51 P=0.04), and very low density lipoprotein (VLDL) (r =−0.66, P=0.009). Also correlation between BMD of spine and HbA1C (r =−0.70, P=0.003) were significant.

Conclusion

Findings of this study show that negative changes in BMD and cardiovascular biomarkers of female athletes with functional hypothalamic menstrual dysfunction could occur if proper therapeutic intervention (including increase in calorie intake, decrease in exercise load or hormonal replacement) will not consider.

Association of CDX1 binding site of periostin gene with bone mineral density and vertebral fracture risk

SUMMARY

Periostin (POSTN) as a regulator of osteoblast differentiation and bone formation may affect susceptibility to osteoporosis. This study suggests POSTN as a candidate gene for bone mineral density (BMD) variation and vertebral fracture risk, which could better our understanding about the genetic pathogenesis of osteoporosis and will be useful in clinic in the future.

INTRODUCTION

The genetic determination of osteoporosis is complex and ill-defined. Periostin (POSTN), an extracellular matrix secreted by osteoblasts and a regulator of osteoblast differentiation and bone formation, may affect susceptibility to osteoporosis.

METHODS

We adopted a tag-single nucleotide polymorphism (SNP) based association method followed by imputation-based verification and identification of a causal variant. The association was investigated in 1,572 subjects with extreme-BMD and replicated in an independent population of 2,509 subjects. BMD was measured by dual X-ray absorptiometry. Vertebral fractures were identified by assessing vertebral height from X-rays of the thoracolumbar spine. Association analyses were performed with PLINK toolset and imputation analyses with MACH software. The top imputation finding was subsequently validated by genotyping. Interactions between POSTN and another BMD-related candidate gene sclerostin (SOST) were analyzed using MDR program and validated by logistical regression analyses. The putative transcription factor binding with target sequence was confirmed by electrophoretic mobility shift assay (EMSA).

RESULTS

Several SNPs of POSTN were associated with BMD or vertebral fractures. The most significant polymorphism was rs9547970, located at the -2,327 bp upstream (P = 6.8 × 10(-4)) of POSTN. Carriers of the minor allele G per copy of rs9547970 had 1.33 higher risk of vertebral fracture (P = 0.007). An interactive effect between POSTN and SOST upon BMD variation was suggested (P < 0.01). A specific binding of CDX1 to the sequence of POSTN with the major allele A of rs9547970 but not the variant G allele was confirmed by EMSA.

CONCLUSIONS

Our results suggest POSTN as a candidate gene for BMD variation and vertebral fracture risk.

The effect of high versus low loading on bone strength in middle life

While bone mass and geometry are largely genetically determined, mechanical loading is considered to be an important additional determinant. This study investigates to what extent very high mechanical loading begun at a young age and sustained afterward can affect tibia bone mass and geometry in middle age. Cohorts from a common ethnic background, with a history of very high and very low tibia bone loading based on an assessment of their activities according their strain levels were compared. The study hypothesis was that the tibia bone density and geometric strength parameters would be greater in the high bone loading cohort. Subjects from a group of elite infantry recruits who sustained a 31% incidence of stress fractures during their basic training in 1983, were reviewed 25 years later. The tibia bone strength of 25 of these soldiers, 11 of whom had sustained stress fractures, was compared to a group of 20 subjects who received exemption from military service in 1982-5 because they were religious scholars and who continued these studies afterwards. Anthropometric measurements were made. The bone density and geometric strength of the tibia was assessed by quantitative computerized tomography (QCT). The average daily dietary intake and metabolic expenditure of subjects were assessed by questionnaires. At the 25 year follow-up soldiers were on an average 3 cm taller than the religious scholars (p=0.02) and had lower abdominal girths (p=0.03). There was no difference in the tibia cortical density between cohorts in spite of the fact that the religious scholars had lower daily calcium intakes (p=0.02). Soldiers had stronger tibias based on geometric engineering criteria. The mean area moments of inertia (p=0.02, p=0.04) and polar moments of inertia (p=0.02) were 16% larger in the soldier cohort. By multivariate regression analysis greater height, weight and daily energy expenditure were related to larger bone geometric strength parameters. According to semipartial eta-square analysis, between 39% to 45% of the variance in the area moments of inertia between the cohorts was attributable to these three parameters. The religious scholars burned less calories daily, principally because they did no sport activity (p=0.001). There was no difference in tibia bone strength parameters between soldiers who did and did not sustain stress fractures in their 1983 basic training. In conclusion, in a middle age population with a common ethnic origin, the high bone loading cohort had stronger tibias than the low bone loading cohort based on larger geometric strength properties and not because of higher cortical density. In spite of being at the extremes of the bone loading spectra, the tibia area moment of inertia of the two cohorts in this study differed by only 16%, with part of this difference attributable to factors other than bone loading. We do not know for sure if the difference in the geometric properties is related to high bone loading or whether people with stronger bones are more likely to engage in high bone loading. Healthy male subjects who sustained stress fractures at a young age do not have weaker tibias at middle age according to QCT measurements.

Genetic variants in the SOX6 gene are associated with bone mineral density in both Caucasian and Chinese populations

SUMMARY

Given the biological function of SOX6 and recent genome-wide association finding, we performed a fine-mapping association analyses to investigate the relationship between SOX6 and BMD both in Caucasian and Chinese populations. We identified many single-nucleotide polymorphisms (SNPs) within or near the SOX6 gene to be significantly associated with hip bone mineral density (BMD).

INTRODUCTION

SOX6 gene is an essential transcription factor in chondrogenesis and cartilage formation. Recent genome-wide association studies (GWAS) detected a SNP (rs7117858) located at the downstream of SOX6 significantly associated with hip BMD.

METHODS

Given the biological function of SOX6 and the GWAS finding, we considered SOX6 as a new candidate for BMD and osteoporosis. Therefore, in this study, we performed a fine-mapping association analyses to investigate the relationship between SNPs within and near the SOX6 gene and BMD at both hip and spine. A total of 301 SNPs were tested in two independent US Caucasian populations (2,286 and 1,000 unrelated subjects, respectively) and a Chinese population (1,627 unrelated Han subjects).

RESULTS

We confirmed that the previously reported rs7117858-A was associated with reduced hip BMD, with combined P value of 2.45 × 10(-4). Besides this SNP, we identified another 19 SNPs within or near the SOX6 gene to be significantly associated with hip BMD after false discovery rate adjustment. The most significant SNP was rs1347677 located at the intron 3 (P = 3.15 × 10(-7)). Seven additional SNPs in high linkage disequilibrium with rs1347677 were also significantly associated with hip BMD. SNPs in SOX6 showed significant skeletal site specificity since no SNP was detected to be associated with spine BMD.

CONCLUSION

Our study identified many SNPs in the SOX6 gene associated with hip BMD even across different ethnicities, which further highlighted the importance of the SOX6 gene influencing BMD variation and provided more information to the understanding of the genetic architecture of osteoporosis.

Whole bone mechanics and bone quality

BACKGROUND

The skeleton plays a critical structural role in bearing functional loads, and failure to do so results in fracture. As we evaluate new therapeutics and consider treatments to prevent skeletal fractures, understanding the basic mechanics underlying whole bone testing and the key principles and characteristics contributing to the structural strength of a bone is critical.

QUESTIONS/PURPOSES

We therefore asked: (1) How are whole bone mechanical tests performed and what are the key outcomes measured? (2) How do the intrinsic characteristics of bone tissue contribute to the mechanical properties of a whole bone? (3) What are the effects of extrinsic characteristics on whole bone mechanical behavior? (4) Do environmental factors affect whole bone mechanical properties?

METHODS

We conducted a PubMed search using specific search terms and limiting our included articles to those related to in vitro testing of whole bones. Basic solid mechanics concepts are summarized in the context of whole bone testing and the determinants of whole bone behavior.

RESULTS

Whole bone mechanical tests measure structural stiffness and strength from load-deformation data. Whole bone stiffness and strength are a function of total bone mass and the tissue geometric distribution and material properties. Age, sex, genetics, diet, and activity contribute to bone structural performance and affect the incidence of skeletal fractures.

CONCLUSIONS

Understanding and preventing skeletal fractures is clinically important. Laboratory tests of whole bone strength are currently the only measures for in vivo fracture prediction. In the future, combined imaging and engineering models may be able to predict whole bone strength noninvasively.

Genome-wide association study using extreme truncate selection identifies novel genes affecting bone mineral density and fracture risk

Osteoporotic fracture is a major cause of morbidity and mortality worldwide. Low bone mineral density (BMD) is a major predisposing factor to fracture and is known to be highly heritable. Site-, gender-, and age-specific genetic effects on BMD are thought to be significant, but have largely not been considered in the design of genome-wide association studies (GWAS) of BMD to date. We report here a GWAS using a novel study design focusing on women of a specific age (postmenopausal women, age 55-85 years), with either extreme high or low hip BMD (age- and gender-adjusted BMD z-scores of +1.5 to +4.0, n = 1055, or -4.0 to -1.5, n = 900), with replication in cohorts of women drawn from the general population (n = 20,898). The study replicates 21 of 26 known BMD-associated genes. Additionally, we report suggestive association of a further six new genetic associations in or around the genes CLCN7, GALNT3, IBSP, LTBP3, RSPO3, and SOX4, with replication in two independent datasets. A novel mouse model with a loss-of-function mutation in GALNT3 is also reported, which has high bone mass, supporting the involvement of this gene in BMD determination. In addition to identifying further genes associated with BMD, this study confirms the efficiency of extreme-truncate selection designs for quantitative trait association studies.

A common variant in fibroblast growth factor binding protein 1 (FGFBP1) is associated with bone mineral density and influences gene expression in vitro

We previously detected strong evidence for linkage of forearm bone mineral density (BMD) to chromosome 4p (lod=4.3) in a set of 29 large Mexican American families. Fibroblast growth factor binding protein 1 (FGFBP1) is a strong candidate gene for bone homeostasis in this region. We sequenced the coding region of FGFBP1 in a subset of our Mexican American study population and performed association studies with BMD on SNPs genotyped in the entire cohort. We then attempted to replicate these findings in an independent study cohort and performed in vitro functional studies on replicated, potentially functional polymorphisms using a luciferase reporter construct to evaluate influence on gene expression. Several SNPs spanning the gene, all in one large block of linkage disequilibrium, were significantly associated with BMD at various skeletal sites (n=872, p=0.001-0.04). The associations were then replicated in an independent population of European ancestry (n=972; p=0.02-0.04). Sex-stratified association analyses in both study populations suggest this association is much stronger in men. Subsequent luciferase reporter gene assays revealed marked differences in FGFBP1 expression among the three common haplotypes. Further experiments revealed that a promoter polymorphism, rs12503796, results in decreased expression of FGFBP1 and inhibits upregulation of the gene by testosterone in vitro. Collectively, these findings suggest that sequence variation in FGFBP1 may contribute to variation in BMD, possibly influencing osteoporosis risk.

Clinical review 2: Genetic determinants of bone density and fracture risk--state of the art and future directions

CONTEXT

Osteoporosis is a common, highly heritable condition that causes substantial morbidity and mortality, the etiopathogenesis of which is poorly understood. Genetic studies are making increasingly rapid progress in identifying the genes involved.

EVIDENCE ACQUISITION AND SYNTHESIS

In this review, we will summarize the current understanding of the genetics of osteoporosis based on publications from PubMed from the year 1987 onward.

CONCLUSIONS

Most genes involved in osteoporosis identified to date encode components of known pathways involved in bone synthesis or resorption, but as the field progresses, new pathways are being identified. Only a small proportion of the total genetic variation involved in osteoporosis has been identified, and new approaches will be required to identify most of the remaining genes.

Association of JAG1 with bone mineral density and osteoporotic fractures: a genome-wide association study and follow-up replication studies

Bone mineral density (BMD), a diagnostic parameter for osteoporosis and a clinical predictor of fracture, is a polygenic trait with high heritability. To identify genetic variants that influence BMD in different ethnic groups, we performed a genome-wide association study (GWAS) on 800 unrelated Southern Chinese women with extreme BMD and carried out follow-up replication studies in six independent study populations of European descent and Asian populations including 18,098 subjects. In the meta-analysis, rs2273061 of the Jagged1 (JAG1) gene was associated with high BMD (p = 5.27 x 10(-8) for lumbar spine [LS] and p = 4.15 x 10(-5) for femoral neck [FN], n = 18,898). This SNP was further found to be associated with the low risk of osteoporotic fracture (p = 0.009, OR = 0.7, 95% CI 0.57-0.93, n = 1881). Region-wide and haplotype analysis showed that the strongest association evidence was from the linkage disequilibrium block 5, which included rs2273061 of the JAG1 gene (p = 8.52 x 10(-9) for LS and 3.47 x 10(-5) at FN). To assess the function of identified variants, an electrophoretic mobility shift assay demonstrated the binding of c-Myc to the "G" but not "A" allele of rs2273061. A mRNA expression study in both human bone-derived cells and peripheral blood mononuclear cells confirmed association of the high BMD-related allele G of rs2273061 with higher JAG1 expression. Our results identify the JAG1 gene as a candidate for BMD regulation in different ethnic groups, and it is a potential key factor for fracture pathogenesis.

Vitamin D receptor gene polymorphisms modulate the skeletal response to vitamin D supplementation in healthy girls

OBJECTIVES

Vitamin D receptor (VDR) gene plays an important role in bone mass regulation. We have previously shown a beneficial effect of vitamin D supplementation on bone mass in girls. This study investigated whether the musculo-skeletal response to Vitamin D was modulated by polymorphisms in VDR gene.

DESIGN

Randomized placebo-controlled trial.

METHODS

179 girls (10-17 years), were randomly assigned to placebo or Vitamin D3 for one year. VDR genotypes were determined in 167 girls using BsmI, TaqI and ApaI restriction enzymes. Bone mass at the spine, hip, forearm and total body, and lean mass were measured by DXA at baseline and at one year.

RESULTS

After one year, VDR gene polymorphisms using Bsm1 and TaqI restriction enzymes were associated with percent changes in bone area, BMC and BMD at multiple skeletal sites in the Vitamin D3 group but not in the placebo group. The least increments were observed in the BB and tt genotypes. No similar effect was observed with ApaI enzyme. This relationship between VDR genotypes and changes in BMD and BMC remained significant after adjustment for puberty, changes in lean mass, height and bone area.

CONCLUSION

VDR gene polymorphisms influence the skeletal response to vitamin D supplementation in healthy adolescent girls.

Bone, muscle, and physical activity: structural equation modeling of relationships and genetic influence with age

Correlations among bone strength, muscle mass, and physical activity suggest that these traits may be modulated by each other and/or by common genetic and/or environmental mechanisms. This study used structural equation modeling (SEM) to explore the extent to which select genetic loci manifest their pleiotropic effects through functional adaptations commonly referred to as Wolff's law. Quantitative trait locus (QTL) analysis was used to identify regions of chromosomes that simultaneously influenced skeletal mechanics, muscle mass, and/or activity-related behaviors in young and aged B6xD2 second-generation (F(2)) mice of both sexes. SEM was used to further study relationships among select QTLs, bone mechanics, muscle mass, and measures of activity. The SEM approach provided the means to numerically decouple the musculoskeletal effects of mechanical loading from the effects of other physiological processes involved in locomotion and physical activity. It was found that muscle mass was a better predictor of bone mechanics in young females, whereas mechanical loading was a better predictor of bone mechanics in older females. An activity-induced loading factor positively predicted the mechanical behavior of hindlimb bones in older males; contrarily, load-free locomotion (i.e., the remaining effects after removing the effects of loading) negatively predicted bone performance. QTLs on chromosomes 4, 7, and 9 seem to exert some of their influence on bone through actions consistent with Wolff's Law. Further exploration of these and other mechanisms through which genes function will aid in development of individualized interventions able to exploit the numerous complex pathways contributing to skeletal health.

Systems analysis of bone

The genetic variants contributing to variability in skeletal traits has been well studied, and several hundred QTLs have been mapped and several genes contributing to trait variation have been identified. However, many questions remain unanswered. In particular, it is unclear whether variation in a single gene leads to alterations in function. Bone is a highly adaptive system and genetic variants affecting one trait are often accompanied by compensatory changes in other traits. The functional interactions among traits, which is known as phenotypic integration, has been observed in many biological systems, including bone. Phenotypic integration is a property of bone that is critically important for establishing a mechanically functional structure that is capable of supporting the forces imparted during daily activities. In this paper, bone is reviewed as a system and primarily in the context of functionality. A better understanding of the system properties of bone will lead to novel targets for future genetic analyses and the identification of genes that are directly responsible for regulating bone strength. This systems analysis has the added benefit of leaving a trail of valuable information about how the skeletal system works. This information will provide novel approaches to assessing skeletal health during growth and aging and for developing novel treatment strategies to reduce the morbidity and mortality associated with fragility fractures.

Genetic and environmental determinants on bone loss in postmenopausal Caucasian women: a 14-year longitudinal twin study

SUMMARY

This longitudinal twin study documented that genetic factors explain 44-56% of the between-individual variance in bone loss at femoral neck, lumbar spine, and forearm in postmenopausal Caucasian women, providing a rationale for identifying the specific genes involved.

INTRODUCTION

Although there is a significant genetic effect on peak BMD, until recently, no substantive studies on heritability of bone loss in human were available. The aim of the study was to estimate the heritability of the bone loss at multiple sites in postmenopausal Caucasian women.

METHODS

Postmenopausal female monozygotic (MZ) and dizygotic (DZ) twins aged 40 or above at baseline were selected from the TwinsUK registry and followed up for an average of 8 years (range 5-14 years). All twins were noncurrent hormone replacement therapy users and not on any osteoporosis treatment. They had dual-energy X-ray absorptiometry (DXA) scans of their hip, lumbar spine, and forearm several times (range 2-9) during the follow-up period. Individual bone losses at femoral neck, lumbar spine, and forearm were estimated by linear regression modeling. Structural equation modeling was utilized to estimate the heritability of the bone loss.

RESULTS

A total of 712 postmenopausal Caucasian female twins (152 MZ and 204 DZ pairs) were included. MZ twins were older and had slightly lower BMD at all sites than DZ twins. DZ twins had slightly higher bone loss at lumbar spine, but similar at femoral neck and forearm compared to MZ twins. Intraclass correlation coefficients (ICC) for the bone loss at all sites were significantly higher in MZ than DZ twin pairs (p = 0.0045, 0.0003, and 0.0007 for femoral neck, lumbar spine, and forearm, respectively), indicating a significant genetic influence on bone loss at these sites. After adjustment for age at baseline and weight change during the follow-up, the heritability estimate was 47% (95% CI 27-63%) for bone loss at femoral neck, 44% (95% CI 27-58%) for lumbar spine, and 56% (95% CI 44-65%) for forearm.

CONCLUSIONS

Our data suggest that up to 56% of the between-individual variance in bone loss is due to genes, providing a rationale to identify specific genetic factors for bone loss.

The human calcium-sensing receptor and interleukin-6 genes are associated with bone mineral density in Chinese

Calcium sensing receptor (CASR) is a central factor involved in calcium metabolism. Interleukin-6 (IL-6) is a pleiotropic cytokine that plays an important role in osteoclast differentiation. Thus, both CASR and IL-6 are important in bone and mineral metabolism and are prominent candidate genes for osteoporosis. The study aimed to test association and/or linkage between the CASR and IL-6 genes with bone mineral density (BMD) variation in a Chinese population. A cytosine-adenine (CA)n repeat polymorphism in the CASR gene and the IL-6 gene was genotyped, respectively, in 1,263 subjects from 402 Chinese nuclear families. Employing tests implemented in the program QTDT (quantitative transmission disequilibrium tests), a significant total association of the CASR (CA)12 allele (P = 0.006) and (CA)18 allele (P = 0.02) with BMD at the femoral neck was found. For the IL-6 gene, significant within-family associations were found between the (CA)14 allele and BMD at the total hip (P = 0.021), the femoral neck (P = 0.041), and the intertrochanteric region (P = 0.029). A significant linkage was also observed between IL-6 CA repeat polymorphism and BMD at the spine (P = 0.001). The results suggest that the CASR gene and the IL-6 gene may have effects on BMD variation in Chinese.

Quantitative ultrasound in the assessment of skeletal status

Quantitative ultrasound (QUS) is a non-invasive technique for the investigation of bone tissue in several pathologies and clinical conditions, especially in the field of osteoporosis. The versatility of the technique, its low cost and lack of ionising radiation have led to the diffusion of this method worldwide. Several studies have been conducted in the last years to investigate the potential of QUS in multiple areas with promising results; the technique has been applied in the prediction of osteoporotic fractures, in monitoring therapies, in the investigation of secondary osteoporosis, in paediatrics, neonatology and genetics. Our review article gives an overview of the most relevant developments in the field of quantitative ultrasound, both in clinical and in experimental settings.

Mapping of the chromosome 17 BMD QTL in the F(2) male mice of MRL/MpJ x SJL/J

Developing treatment strategies for osteoporosis would be facilitated by identifying genes regulating bone mineral density (BMD). One way to do so is through quantitative trait locus (QTL) mapping. However, there are sex differences in terms of the presence/absence and locations of BMD QTLs. In a previous study, our group identified a BMD QTL on chromosome 17 in the F(2) female mice of the MRL/MpJ x SJL/J cross. Here, we determined whether it was also present in the male mice of the same cross. Furthermore, we also intended to reduce the QTL region by increasing marker density. Interval mapping showed that the same QTL based on chromosomal positions was present in the male mice, with logarithmic odds (LOD) scores of 4.0 for femur BMD and 5.2 for total body BMD. Although there was a body weight QTL at the same location, the BMD QTL was not affected by the adjustment for body weight. Mapping with increased marker density indicated a most likely region of 35-55 Mb for this QTL. There were also co-localized QTLs for femur length, femur periosteal circumference (PC) and total body bone area, suggesting possibility of pleiotropy. Runx2 and VEGFA are strong candidate genes located within this QTL region.

Bivariate whole genome linkage analyses for total body lean mass and BMD

A genome-wide bivariate analysis was conducted for TBLM and BMD at the spine and hip in a large white sample. We found some QTLs shared by TBLM and BMD in the entire sample and the sex-specific subgroups, and QTLs with potential pleiotropy were disclosed.

INTRODUCTION

Previous studies suggested that total body lean mass (TBLM) and BMD are highly genetically correlated. However, the specific shared genetic factors between TBLM and BMD are unknown.

MATERIALS AND METHODS

To identify the specific quantitative trait loci (QTLs) shared by TBLM and BMD at the spine (L1-L4) and total hip, we performed bivariate whole genome linkage analysis (WGLA) in a large sample involving 4498 white subjects of European origin.

RESULTS

Multipoint bivariate linkage analyses for 22 autosomes showed evidence of significant linkage with an LOD score of 4.86 at chromosome region 15q13 for TBLM and spine BMD in women, and suggestive linkage findings (LOD > 2.2) at 7p22 for TBLM and spine BMD for the entire sample, at 7q32 for TBLM and BMD at both spine and hip in women, and at 7q21 and 13p11 for TBLM and BMD at both spine and hip in men. Two-point linkage analyses for chromosome X also showed significant linkage signals at several regions such as Xq25. Complete pleiotropy (a single locus influencing both traits) was suggested at 7q32 and 13q11 for TBLM and BMD. Additionally, complete co-incident linkage (separate tightly clustered loci each influencing a single trait) was detected at 7p22 for TBLM and spine BMD.

CONCLUSIONS

We identified several genomic regions shared by TBLM and BMD in whites. Further studies may focus on fine mapping and identification of the specific QTLs in these candidate genomic regions.

Structural parameters and mechanical strength of cancellous bone in the femoral head in osteoarthritis do not depend on age

For normal bone, aging has been associated with a decrease of both density and failure strength, and with the development of pathologies such as osteoporosis. Conversely, it has been reported that another common disease, osteoarthritis, may alter these age-related changes in cancellous bone, suggesting that it may have a protective role against osteoporosis and the correspondent fracture risk. It was reported that in the principal compressive region of the femoral head in osteoarthritis the bone density does not depend on age. However, it is not clear if this independence on age of the cancellous bone density corresponds also to a reduced dependence on age of the strength to failure. The present work examined cancellous bone from the principal compressive region of the femoral head of 37 patients having severe osteoarthritis. The aim was (1) to investigate the dependence on age of both the structural parameters and the ultimate stress and (2) to investigate the relationships between the ultimate stress and the structural parameters. Using X-ray microcomputed tomography, three-dimensional structural parameters, such as bone volume fraction, direct trabecular thickness and structure model index were calculated. Then the specimens were compressed to failure to determine the ultimate stress. It was found that none of the investigated structural parameters did depend on age, and also the ultimate stress did not depend on age (p>0.05 for all regressions on age). In addition, the ultimate stress was significantly correlated with the structural parameters, primary with the minimum bone volume fraction and the average bone volume fraction (R(2)=0.95 and R(2)=0.84, respectively). These findings show that severe osteoarthritis or a related factor may change the age dependences of both the structural parameters and the mechanical properties usually reported for normal cancellous bone. These results suggest for this pathology to have a protective role against the age-related decrease in density, the age-related deterioration of the microarchitecture and the age-related decrease of the failure strength for the cancellous bone in the principal compressive region of the human femoral head.

Chromosome 2q32 may harbor a QTL affecting BMD variation at different skeletal sites

BMDs at different skeletal sites share some common genetic determinants. Using PCA and bivariate linkage analysis, we identified a QTL on chromosome 2q32 with significant pleiotropic effects on BMDs at different skeletal sites.

INTRODUCTION

BMDs at the hip, spine, and forearm are genetically correlated, suggesting the existence of quantitative trait loci (QTLs) with concurrent effects on BMDs at these three skeletal sites. Consequently, it is important to identify these QTLs in the human genome and, for those implicated QTLs, it is important to differentiate between pleiotropic effects, caused by a single gene that concurrently effects these traits, and co-incident linkage, caused by multiple, closely linked, genes that independently effect these traits.

MATERIALS AND METHODS

For a sample of 451 American white pedigrees made up of 4,498 individuals, we evaluated the correlations between BMDs at the three skeletal sites. We carried out principal component analysis (PCA) for the three correlated traits and obtained a major component, PC1, which accounts for >75% of the co-variation of BMDs at the three sites. We subsequently conducted a whole genome linkage scan for PC1 and performed bivariate linkage analysis for pairs of the three traits (i.e., forearm/spine BMD, hip/forearm BMD, and hip/spine BMD).

RESULTS

Chromosome region 2q32, near the marker GATA65C03M, showed strong linkage to PC1 (LOD = 3.35). Subsequent bivariate linkage analysis substantiated linkage at 2q32 for each trait pair (LOD scores were 2.65, 2.42, and 2.13 for forearm/spine BMD, hip/forearm BMD, and hip/spine BMD, respectively). Further analyses rejected the hypothesis of co-incident linkage (p(0)[forearm/spine] = 0.0005, p(0)[hip/forearm] = 0.004, p(0)(hip/spine] = 0.001) but failed to reject the hypothesis of pleiotropy (p(1)[forearm/spine] = 0.35, p(1)[hip/forearm] = 0.07, p(1)[hip/spine] = 0.15).

CONCLUSIONS

Our results strongly support the conclusion that chromosome region 2q32 may harbor a QTL with pleiotropic effects on BMDs at different skeletal sites.

Heritability of BMD of femoral neck and lumbar spine: a multivariate twin study of Finnish men

Of the 80% variation in BMD among male twins that is caused by genetics, part was explained by genetic influences on lifting strength and lean body mass/height. Lifting strength was significant in both the femoral and spine BMD and body weight only for lumbar BMD.

INTRODUCTION

The dominant role of heritability in BMD has been shown in twin studies among women. However, the mechanisms of genetic influences are poorly understood. BMD is associated with lean body mass and muscle strength, which both have a genetic component, but the relative effects of muscle strength and lean body mass/height on the total genetic and environmental variations influencing BMD of men are unclear.

MATERIALS AND METHODS

Measurements of BMD from a DXA scanner on a representative sample of 147 monozygotic and 153 dizygotic male twin pairs (age, 35-70 yr) were related to a variety of anthropometric and behavioral covariates and interview data. Data were analyzed with univariate modeling of genetic characteristics, bivariate modeling of covariates that were significant in univariate models, and multivariate modeling of the simultaneous effects of significant covariates from the bivariate models.

RESULTS

Heritability influences were estimated to account for 75% of the variance in femoral BMD and 83% in lumbar BMD. Univariate and bivariate modeling showed that, of the factors studied, only lifting force and lean body mass/height had statistically significant influences. Of the total genetic variation in femoral BMD, lifting force explained 9%, and lean body mass/height 18%; the proportions for lumbar BMD were 9% and 11%, respectively. Of the total environmental variation, the correlation with isokinetic lifting force explained 9% for femoral BMD and 10% for lumbar BMD. The genetic correlations between lifting force and femoral and lumbar BMD were approximately 0.3, as were the environmental correlations of isokinetic lifting force and femoral and lumbar BMD and of lean body mass/height and femoral BMD. The environmental correlation of lean body mass/height and femoral BMD was not significant.

CONCLUSIONS

Lifting force had effects on both femoral and lumbar BMD. Body weight was important, but only for lumbar BMD. Muscle strength may have the best potential for modification among behavioral factors to increase both femoral and lumbar BMD.

A comparison of fatigue failure responses of old versus middle-aged lumbar motion segments in simulated flexed lifting

STUDY DESIGN

Survival analysis techniques were used to compare the fatigue failure responses of elderly motion segments to a middle-aged sample.

OBJECTIVES

To compare fatigue life of a middle-aged sample of lumbosacral motion segments to a previously tested elderly cohort. An additional objective was to evaluate the influence of bone mineral content on cycles to failure.

SUMMARY OF BACKGROUND DATA

A previous investigation evaluated fatigue failure responses of 36 elderly lumbosacral motion segments (average age, 81 +/- 8 years) subjected to spinal loads estimated when lifting a 9-kg load in 3 torso flexion angles (0 degrees, 22.5 degrees, and 45 degrees). Results demonstrated rapid fatigue failure with increased torso flexion; however, a key limitation of this study was the old age of the specimens.

METHODS

Each lumbosacral spine was dissected into 3 motion segments (L1-L2, L3-L4, and L5-S1). Motion segments within each spine were randomly assigned to a spinal loading condition corresponding to lifting 9 kg in 3 torso flexion angles (0 degrees, 22.5 degrees, or 45 degrees). Motion segments were statically loaded and allowed to creep for 15 minutes, then cyclically loaded at 0.33 Hz. Fatigue life was taken as the number of cycles to failure (10 mm displacement after creep loading).

RESULTS

Compared with the older sample of spines, the middle-aged sample exhibited increased fatigue life (cycles to failure) in all the torso flexion conditions. Increased fatigue life of the middle-aged specimens was associated with the increased bone mineral content (BMC) in younger motion segments (mean +/- SD, 30.7 +/- 11.1 g per motion segment vs. 27.8 +/- 9.4 g). Increasing bone mineral content had a protective influence with each additional gram increasing survival times by approximately 12%.

CONCLUSION

Younger motion segments survive considerably longer when exposed to similar spine loading conditions that simulate repetitive lifting in neutral and flexed torso postures, primarily associated with the increased bone mineral content possessed by younger motion segments. Cycles to failure of young specimens at 22.5 degrees flexion were similar to that of older specimens at 0 degrees flexion, and survivorship of young specimens at 45 degrees flexion was similar to the older cohort at 22.5 degrees.

The female football player, disordered eating, menstrual function and bone health

Most female football players are healthy. However, recent findings from our studies on Norwegian female elite athletes also show that football players are dieting and experiencing eating disorders, menstrual dysfunction and stress fractures. Dieting behaviour and lack of knowledge of the energy needs of the athlete often leads to energy deficit, menstrual dysfunction and increased risk of bone mass loss. Although dieting, eating disorders and menstrual dysfunction are less common than in many other sports, it is important to be aware of the problem as eating disorders in female athletes can easily be missed. Therefore, individuals, including the players themselves, coaches, administrators and family members, who are involved in competitive football, should be educated about the three interrelated components of the female athlete triad (disordered eating, menstrual dysfunction and low bone mass), and strategies should be developed to prevent, recognise and treat the triad components.

AHSG gene polymorphisms are associated with bone mineral density in Caucasian nuclear families

PURPOSE

To investigate the role of alpha2-HS glycoprotein (AHSG) gene on bone mineral density (BMD) variation.

METHODS

A total of 665 subjects from 157 Caucasian nuclear families were genotyped at the AHSG NlaIII, SacI sites. The association and linkage between the single SNP markers and haplotypes constructed by two markers in this gene and BMDs at the spine and hip were determined by using quantitative transmission disequilibrium test (QTDT).

RESULTS

Significant within-family associations were obtained for spine BMD at both of studied markers (P = 0.036 and 0.005 at the NlaIII and SacI sites, respectively). Significant (P = 0.008 at the NlaIII locus) (P = 0.004 at the SacI locus) total associations at spine BMD were detected. Haplotype analyses confirmed those within-family and total association.

CONCLUSIONS

These data suggest the polymorphisms in the AHSG gene may have effects on BMD variation in Caucasian population.

Familial aggregation of forearm bone mineral density in Chinese

Osteoporosis is a major public health concern and its prevalence can be predicted based on forearm bone mineral density (BMD). This study is to investigate the familial aggregation of forearm BMD in a population-based, cross-sectional study in Anhui, China. Information on sociodemographic and environmental variables was obtained from 1,636 subjects from 409 nuclear families (including mother, father, and their first two children) by a standardized questionnaire. The forearm BMD was measured by peripheral dual-energy X-ray absorptiometry (pDXA). Using generalized additive models with a sequential adjustment for covariates, it was clearly indicated that the forearm BMD of the mother, the father, and the first sibling each had a significant and independent relation to the forearm BMD of the second sibling. Furthermore, using multiple logistic regression, the second sibling had an odds ratio (OR) of 5.3 (95%CI: 2.0-14.5) of having an extremely low (bottom 10th percentile) proximal forearm BMD and an OR of 4.3 (95%CI: 1.6-12.0) of having an extremely low distal forearm BMD when the parental mean forearm BMD was low and the first sibling's forearm BMD was low. Our findings showing strong familial aggregation of both proximal and distal forearm BMD values suggest that genetic factors play a significant role in determining both traits.

Determinants of bone mineral density in Chinese-American women

SUMMARY

Few data are available regarding bone mineral density (BMD) and its determinants among Chinese Americans. We identified determinants of BMD among 359 Chinese-American women in order to identify risk factors for low BMD in this burgeoning population. BMD in Chinese-American women is influenced by a number of factors, including immigration.

INTRODUCTION

Osteoporosis and low BMD are common among Chinese women, including Chinese Americans, who are a growing population at risk for osteoporosis in the US. Few data are available regarding BMD and its determinants among Chinese-American women.

METHODS

In this study, we examined predictors of BMD in 359 ambulatory Chinese-American women, ages 20-90, using stepwise multiple regression analysis. Variables in the model included age, weight, height, menarche age, years since menopause, immigration age, years in US, percentage of life in US, number of pregnancies, oral contraceptive use, family history of osteoporosis, family history of hip fracture, daily calcium intake, exercise, time outdoors, alcohol consumption and tobacco use.

RESULTS

Among premenopausal women, weight was the strongest predictor of BMD, accounting for 10.5% of the variance at the lumbar spine (LS), 15.2% at the total hip (TH) and 16.6% at the femoral neck (FN). Time outdoors was also a positive predictor of BMD (1.4% at LS, 2.8% at TH and 1.6% at FN), while family history of osteoporosis (1.4% at TH) and age (3.7% at FN) were negative predictors. Among postmenopausal women, greater BMD at the LS and TH was associated with greater weight and earlier immigration age. Weight accounted for 16.4% of the variance at the LS and 19.8% at the TH; immigration age accounted for 3.1% of the variance at the LS and 4.1% at the TH. At the FN, years since menopause and weight were predictors of BMD, accounting for 14.4% and 8.7% of the variance, respectively. While older age at immigration had a negative effect on BMD, years in and proportion of life in the United States were not significant predictors of BMD.

CONCLUSIONS

Bone mineral density in Chinese-American women is influenced by a number of biological and lifestyle factors, including immigration. The results of this study provide new insights into risk factors for low bone density as they relate to environmental determinants in the growing population of Chinese-American women.

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.

Detecting novel bone density and bone size quantitative trait loci using a cross of MRL/MpJ and CAST/EiJ inbred mice

Most previous studies to identify loci involved in bone mineral density (BMD) regulation have used inbred strains with high and low BMD in generating F(2) mice. However, differences in BMD may not be a requirement in selecting parental strains for BMD quantitative trait loci (QTL) studies. In this study, we intended to identify novel QTL using a cross of two strains, MRL/MpJ (MRL) and CAST/EiJ (CAST), both of which exhibit relatively high BMD when compared to previously used strains. In addition, CAST was genetically distinct. We generated 328 MRL x CAST F(2) mice of both sexes and measured femur BMD and periosteal circumference (PC) using peripheral quantitative computed tomography. Whole-genome genotyping was performed with 86 microsatellite markers. A new BMD QTL on chromosome 10 and another suggestive one on chromosome 15 were identified. A significant femur PC QTL identified on chromosome 9 and a suggestive one on chromosome 2 were similar to those detected in MRL x SJL. QTL were also identified for other femur and forearm bone density and bone size phenotypes, some of which were colocalized within the same chromosomal positions as those for femur BMD and femur PC. This study demonstrates the utility of crosses involving inbred strains of mice which exhibit a similar phenotype in QTL identification.

CYP17 and COMT gene polymorphisms can influence bone directly, or indirectly through their effects on endogenous sex steroids, in postmenopausal Japanese women

We aimed to assess whether circulating sex steroids would influence bone density and bone loss, whether part of this influence could be explained by genetic variation measured as polymorphisms in candidate genes affecting circulating hormone levels, or whether gene polymorphisms would have direct effects on bone in 229 postmenopausal Japanese women aged 46 years and over who had been followed for eight years (Yokohama Cohort). Bone mineral density (BMD) in the lumbar spine (L), femoral neck (FN), total hip (T) and distal radius (R) was measured every year, and endogenous sex steroid levels were determined at the start of the study. We investigated the polymorphisms of estrogen-metabolizing enzyme gene, CYP17; estrogen biosynthesis (high activity, A2/A2), CYP1A1; hydroxylation (high inducibility, vt/vt) and COMT; inactivation (low activity, L/L) with PCR-based restriction fragment length polymorphism assays. Dehydroepiandrosterone (DHEA) and androstenedione (AND) levels significantly correlated with bone density in both the axial (L) and the appendicular skeleton (FN, T and R) (r=0.194-0.229; P<0.05) whereas estradiol (E2) and AND showed significant correlations with bone change only at the axial skeleton (r=0.205 and r=-0.139, respectively; P<0.05) on the total cohort. These correlations remained significant in thin/normal-weight women [body mass index (BMI) <25 kg/m2)] even after adjustment for years since menopause (YSM) and BMI or age and BMI, suggesting an interaction of BMI and sex steroid/BMD association. On the total cohort, a difference in endogenous DHEA levels between CYP17 homozygote A2 and non-homozygote A2; an increasing trend in AND levels from COMT L/L, L/H, to H/H; and a difference in TS level between COMT homozygote L and non-homozygote L were separately observed. All observations were significant for unadjusted and adjusted analysis, except for COMT and TS. In thin/normal-weight women (BMI <25 kg/m2), the same effects of CYP17 genotypes on DHEA were observed as on the total cohort. CYP17 and COMT genes showed some direct influence on bone density. Mean percent change in T-BMD was negative for CYP17 non-homozygote A2 in contrast to a positive value for homozygote A2. Mean percent change in R-BMD showed the difference between COMT homozygote L and non-homozygote L with a larger decrease for the homozygote L. Together, CYP17 and COMT genotypes might have some effect on bone both directly and indirectly through their effects on endogenous sex steroids in postmenopausal Japanese women.

Association analysis of the polymorphisms of the VDR gene with bone mineral density and the occurrence of fractures

Associations of the FokI, BsmI, ApaI, and TaqI polymorphisms of the vitamin D receptor (VDR) gene with the bone mineral density (BMD) of the lumbar part of the spinal column (BMD LS) and the neck of the femur (BMD FN), and with the occurrence of fractures, were studied using the polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) analysis on DNA isolated from peripheral blood of 239 women and 40 men from the region of western Poland. Three polymorphisms of the 3' end of the VDR gene (BsmI, ApaI, TaqI) indicated a strong linkage disequilibrium. Association analysis of the VDR gene FokI polymorphism with BMD LS showed a dose effect of allele f. The association of the bAT haplotype of the BsmI, ApaI, and TaqI polymorphisms of the VDR gene with BMD FN was statistically significant. The association of the ApaI polymorphism with the occurrence of fractures was observed. Associations were also observed between the occurrence of fractures and the baT haplotypes of the VDR gene.

Genomic regions identified for BMD in a large sample including epistatic interactions and gender-specific effects

A genome-wide linkage scan was conducted using a large white sample to identify QTLs for BMD. We found QTLs in the total sample and the gender-specific subgroups, as well as significant epistatic interactions underlying BMD variations.

INTRODUCTION

Low BMD is an important risk factor for osteoporosis and under strong genetic control.

MATERIALS AND METHODS

To identify quantitative trait loci (QTLs) for regulation of BMD, we performed a large-scale whole genome linkage scan (WGS) involving 4126 individuals from 451 families. In addition to the conventional linkage analyses in the total combined sample of males and females, we conducted epistatic interaction analyses and gender-specific linkage analyses.

RESULTS

Significant linkage was detected on 5q23 for wrist BMD (LOD = 3.39) and 15q13 for female spine BMD (LOD = 4.49). For spine BMD, we revealed significant epistatic interactions between 3p25 and 2q32 (p = 0.0022) and between 3p25 and 11q23 (p = 0.0007). We replicated several genomic regions that showed linkage with BMD in previous studies by others and ours, such as 3p21, 1p36, and Xq27.

CONCLUSIONS

This study highlights the importance of large sample size, incorporation of epistatic interaction, and consideration of gender-specific effects in identifying QTLs for BMD variation. The results of this study provide a foundation for the future fine mapping and gene identification in our population.

The effect of bilateral oophorectomy on bone mineral density

The objective of this study is to investigate the effect of bilateral oophorectomy with total abdominal hysterectomy on bone loss, comparing the cases having surgery before and after the menopause. Bone mineral density (BMD) measurements were obtained from the lumbar spine and femoral neck of totally 127 cases. Out of 127, 105 had surgery before menopause and 22 cases were operated on postmenopausally. The results were compared with the USA normal values. The average age of surgical menopause (SM) cases was 48.45 years with a mean duration of menopause of 5.77 years. The average height and weight were 157.67 cm and 68.19 kg, respectively. The average age of cases having surgery after menopause (SAM) was 62.45 years with a mean duration of 5.59 years after the surgery (duration after menopause is 13.23 years). The average height and weight were 157.45 cm and 73.55 kg, respectively. The average of BMD measurements of lumbar spines L2-L4 was 1.04 gr/cm(2) (BMD = 85.65% and T score = -0.96) in the cases with SM. On the contrary, the average of the BMD measurements of lumbar spines L2-L4 was 1.05 gr/cm(2) (BMD = 101.14% and T score = 0.24) in the cases with SAM. The average of the BMD measurements of femoral neck was 0.85 gr/cm(2) (BMD = 91.39% and T score = -0.64) in the cases with SM. On the contrary, the average of the BMD measurements of femoral neck was 0.82 gr/cm(2) (BMD = 96.69% and T score = -0.31) in the cases with SAM. The bilateral oophorectomy as a surgical procedure is not a statistically significant factor for the acceleration of the bone loss. The main points are the age and the duration of menopause of the patient affecting the bone loss if the surgery is performed before menopause.