Genetic and environmental determinants of volumetric and areal BMD in multi-generational families of African ancestry: the Tobago Family Health Study

pQCT bone geometry and strength: population epidemiology and concordance in Australian children aged 11-12 years and their parents

OBJECTIVES

To describe the epidemiology and concordance of bone health in a population-based sample of Australian parent-child dyads at child age 11-12 years.

DESIGN

Population-based cross-sectional study (the Child Health CheckPoint) nested between waves 6 and 7 of the Longitudinal Study of Australian Children (LSAC).

SETTING

Assessment centres in seven cities around Australia, February 2015-March 2016.

PARTICIPANTS

of all participating CheckPoint families (n=1874), bone data were available for 1222 dyads (1271 children, 50% girls; 1250 parents, 86% mothers).

OUTCOME MEASURES

Peripheral quantitative CT (pQCT) of the non-dominant leg scanned at the 4% (distal) and 66% (mid-calf) tibial sites. Stratec XCT 2000 software generated estimates of bone density, geometry and polar stress-strain index.Parent-child concordance were assessed using Pearson's correlation coefficients and multivariable linear regression models. Percentiles were determined using survey weights. Survey weights and methods accounted for LSAC's complex sampling, stratification and clustering within postcodes.

RESULTS

Concordances were greater for the geometric pQCT parameters (periosteal circumference 0.38, 95% CI 0.33 to 0.43; endosteal circumference 0.42, 95% CI 0.37 to 0.47; total cross-sectional area 0.37, 95% CI 0.32 to 0.42) than density (cortical density 0.25, 95% CI 0.19 to 0.30). Mother-child and father-child values were similar. Relationships attenuated only slightly on adjustment for age, sex and body mass index. Percentiles and concordance are presented for the whole sample and by sex.

CONCLUSIONS

There is strong parent-child concordance in bone geometry and, to a lesser extent, density even before the period of peak adolescent bone deposition. This geometrical concordance suggests that future intergenerational bone studies could consider using pQCT rather than the more commonly used dual X-ray absorptiometry (DXA).

BMP7 gene polymorphisms are not associated with bone mineral density or osteoporotic fractures in postmenopausal Chinese women

AIM

A previous study shows that bone morphogenetic protein 7 (BMP7) gene polymorphisms are associated with bone mineral density (BMD) in 920 European Americans. To determine the association of BMP7 polymorphisms and BMD and osteoporotic fracture susceptibility, we performed a case-control association study in postmenopausal Chinese women with or without osteoporotic fracture.

METHODS

A total of 3815 unrelated postmenopausal Chinese women (1238 with osteoporotic fracture and 2577 healthy controls) were recruited. BMDs of the lumbar spine 1-4 (L1-4) and proximal femur (including total hip and femoral neck) were measured using dual-energy X-ray absorptiometry. Eight tagging single nucleotide polymorphisms (SNPs) in BMP7 gene, including rs11086598, rs4811822, rs12481628, rs6025447, rs230205, rs17404303, rs162316 and rs6127980, were genotyped.

RESULTS

Among the 8 SNPs, rs6025447 and rs230205 were associated with total hip BMD (P=0.013 and 0.045, respectively). However, the associations became statistically insignificant after adjusting for age, height and weight. The TGTG haplotype of BMP7 gene was associated with total hip BMD (P=0.032), even after adjusting for age, height and weight (P=0.048); but the association was insignificant after performing the Bonferroni multiple-significance-test correction. Moreover, the 8 SNPs and 9 haplotypes of BMP7 gene were not associated with L1-4 or femoral neck BMD or osteoporotic fracture.

CONCLUSION

This large-sample case-control association study suggests that the common genetic polymorphisms of BMP7 gene are not major contributors to variations in BMD or osteoporotic fracture in postmenopausal Chinese women.

Genetic and environmental variances of bone microarchitecture and bone remodeling markers: a twin study

All genetic and environmental factors contributing to differences in bone structure between individuals mediate their effects through the final common cellular pathway of bone modeling and remodeling. We hypothesized that genetic factors account for most of the population variance of cortical and trabecular microstructure, in particular intracortical porosity and medullary size - void volumes (porosity), which establish the internal bone surface areas or interfaces upon which modeling and remodeling deposit or remove bone to configure bone microarchitecture. Microarchitecture of the distal tibia and distal radius and remodeling markers were measured for 95 monozygotic (MZ) and 66 dizygotic (DZ) white female twin pairs aged 40 to 61 years. Images obtained using high-resolution peripheral quantitative computed tomography were analyzed using StrAx1.0, a nonthreshold-based software that quantifies cortical matrix and porosity. Genetic and environmental components of variance were estimated under the assumptions of the classic twin model. The data were consistent with the proportion of variance accounted for by genetic factors being: 72% to 81% (standard errors ∼18%) for the distal tibial total, cortical, and medullary cross-sectional area (CSA); 67% and 61% for total cortical porosity, before and after adjusting for total CSA, respectively; 51% for trabecular volumetric bone mineral density (vBMD; all p < 0.001). For the corresponding distal radius traits, genetic factors accounted for 47% to 68% of the variance (all p ≤ 0.001). Cross-twin cross-trait correlations between tibial cortical porosity and medullary CSA were higher for MZ (rMZ  = 0.49) than DZ (rDZ  = 0.27) pairs before (p = 0.024), but not after (p = 0.258), adjusting for total CSA. For the remodeling markers, the data were consistent with genetic factors accounting for 55% to 62% of the variance. We infer that middle-aged women differ in their bone microarchitecture and remodeling markers more because of differences in their genetic factors than differences in their environment.

Influence of nutrition and lifestyle on bone mineral density in children from adoptive and biological families

Background

The precise contributions of hereditary and environmental factors to bone density are not known. We compared lifestyle predictors of bone density among adopted and biological children.

Methods

The study comprised 18 adopted children (mean [SD] age, 14.0 [4.1] years) with their non-biological parents and 17 children with their biological parents. Bone mineral density (BMD; g/cm²) was measured at the lumbar spine, total femur, and distal radius. Nutritional intake was assessed by food frequency questionnaire. Information on smoking and physical activity was obtained by questionnaire.

Results

Intakes of all nutrients, corrected for energy intake, and all lifestyle characteristics except sleep duration were similar in biological children and their parents. As compared with their parents, adopted children had significantly different energy, protein, and calcium intakes and physical activity levels. In a regression model, BMD z scores of adopted children and their parents were significantly inversely associated at the spine and total femur, whereas BMD z scores of biological children and their parents were significantly positively associated at all measurement sites. The greatest proportion of total variance in BMD was accounted for by calcium intake among adopted children and by parental BMD among biological children.

Conclusions

For some lifestyle characteristics and nutrient intakes, the differences between parents and children were more obvious among adoptive families than among biological families. The most important lifestyle predictor of bone density was calcium intake.

Relative influence of heritability, environment and genetics on serum sclerostin

SUMMARY

We determined factors associated with serum sclerostin in 446 Afro-Caribbean family members. Age, weight, sex, diabetes and kidney function were associated with sclerostin. Sclerostin was heritable, and nine SNPs in the SOST gene region were associated with sclerostin. Variation in serum sclerostin is a heritable factor that is determined by both genetic and environmental factors.

INTRODUCTION

Sclerostin, encoded by the SOST gene, is a Wnt inhibitor that regulates bone mineralization and is a candidate gene locus for osteoporosis. However, little is known about the genetic and non-genetic sources of inter-individual variation in serum sclerostin levels.

METHODS

Serum sclerostin was measured in 446 Afro-Caribbean men and women aged 18+ from seven large, multigenerational families (mean family size, 64; 3,840 relative pairs). Thirty-six common single nucleotide polymorphisms (SNP) were genotyped within a 100 kb region encompassing the gene encoding sclerostin (SOST). Genetic and non-genetic factors were tested for association with serum sclerostin.

RESULTS

Mean serum sclerostin was 41.3 pmol/l and was greater in men than in women (P < 0.05). Factors associated with higher serum sclerostin were increased age and body weight, male sex, diabetes and decreased glomerular filtration rate, which collectively accounted for 25.4 % of its variation. Residual genetic heritability of serum sclerostin was 0.393 (P < 0.0001). Nine SNPs reached nominal significance with sclerostin. Three of those nine SNPs represented independent association signals (rs851056, rs41455049 and rs9909172), which accounted for 7.8 % of the phenotypic variation in sclerostin, although none of these SNPs surpassed a Bonferroni correction for multiple comparisons.

CONCLUSIONS

Serum sclerostin is a heritable trait that is also determined by environmental factors including age, sex, adiposity, diabetes and kidney function. Three independent common SNPs within the SOST region may collectively account for a significant proportion of the variation in serum sclerostin.

Genetic epidemiology and genome-wide linkage analysis of carotid artery ultrasound traits in multigenerational African ancestry families

OBJECTIVE

Intima-media thickness, adventitial diameter and lumen diameter are indicators of cardiovascular disease risk. The influence of genetic factors on these measures in African ancestry populations is not well defined. Therefore, we estimated heritability and performed genome-wide linkage analysis of carotid ultrasound traits in 7 multigenerational families of African ancestry.

METHODS

A total of 395 individuals (7 pedigrees; mean family size = 56; 2392 relative pairs) aged ≥18 years had a common carotid artery ultrasound scan. Statistical analyses were conducted using pedigree-based maximum likelihood methods.

RESULTS

Significant covariates included age, sex, body mass index or height and waist, and systolic blood pressure. Residual heritabilities ranged from 0.35 ± 0.10 to 0.64 ± 0.12 (P < 0.0001). We identified a novel quantitative trait locus for adventitial and lumen diameters on chromosome 11 (max LOD = 4.09, 133 cm).

CONCLUSION

Further fine mapping of this region may identify specific mutations predisposing to subclinical vascular disease among African ancestry individuals.

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.

Site-specific differences in bone mineral density in black and white premenopausal South African women

SUMMARY

We examined ethnic differences in bone mineral density (BMD) and the contribution of body composition, lifestyle and socioeconomic factors in South African women. Femoral neck and total hip BMD were higher, but lumbar spine BMD was lower in black women, with body composition, lifestyle and socioeconomic status (SES) factors contributing differently in ethnic groups.

INTRODUCTION

There is a paucity of data on the relative contribution of body composition, lifestyle factors and SES, unique to different ethnic groups in South Africa, to BMD. We examined differences in femoral neck (FN), total hip (TH) and lumbar spine (LS) BMD between black and white premenopausal South African women and the associations between BMD and body composition, lifestyle factors and SES in these two ethnic groups.

METHODS

BMD and body composition were measured in 240 black (27 ± 7; 18-45 years) and 187 white (31 ± 8; 18-45 years) women using dual-energy X-ray absorptiometry. Questionnaires were administered to examine SES, physical activity and dietary intake.

RESULTS

After co-varying for age, FN and TH were higher in black than white women (FN 0.882 ± 0.128 vs. 0.827 ± 0.116 g/cm(2), P < 0.001; TH 0.970 ± 0.130 vs. 0.943 ± 0.124 g/cm(2), P = 0.018). When adjusting for ethnic differences in body composition, LS was higher in white than black women. In black women, fat-free soft tissue mass, SES and injectable contraceptive use explained 33-42% of the variance in BMD at the hip sites and 22% at the LS. In white women, fat-free soft tissue mass and leisure activity explained 24-30% of the variance in BMD at the hip sites, whereas fat mass, leisure activity and oral contraceptive use explained 11% of the variance at the LS.

CONCLUSION

FN and TH BMD were higher, but LS BMD was lower in black than white South African women with body composition, lifestyle and SES factors contributing differently to BMD in these women.

Cadmium is more toxic on volume bone mineral density than tissue bone mineral density

It has been showed that Cd induces low areal bone mineral density, but we do not know the effect of Cd on cubic bone density. This study was aimed to investigate the effects of Cd on volumetric bone mineral density (VBMD) and tissue bone mineral density (TBMD) in male rats. Twenty-four Sprague-Dawley male rats were randomly divided into four groups that were given cadmium chloride by subcutaneous injection at doses of 0, 0.1, 0.5, and 1.5 mg/kg body weight for 8 weeks, respectively. Then, microcomputed tomography scanning was performed on the proximal tibia, and region of interest was reconstructed using microview software. The VBMD, bone volume fraction of rats treated with 1.5 mg Cd/kg, were significantly decreased compared to control (p < 0.01). The trabecular numbers of rats exposed to Cd were all significantly decreased relative to control (p < 0.05). The trabecular separation of rats treated with 1.5 mg Cd/kg was obviously increased compared to control (p < 0.01). However, Cd had no obvious influence on TBMD. Cd induced low VBMD but not TBMD; Cd effect on bone may be related with trabecular bone loss but not with trabecular bone demineralization.

Influence of polymorphisms in the RANKL/RANK/OPG signaling pathway on volumetric bone mineral density and bone geometry at the forearm in men

We sought to determine the influence of single-nucleotide polymorphisms (SNPs) in RANKL, RANK, and OPG on volumetric bone mineral density (vBMD) and bone geometry at the radius in men. Pairwise tag SNPs (r (2) ≥ 0.8) for RANKL (n = 8), RANK (n = 44), and OPG (n = 22) and five SNPs near RANKL and OPG strongly associated with areal BMD in genomewide association studies were previously genotyped in men aged 40-79 years in the European Male Ageing Study (EMAS). Here, these SNPs were analyzed in a subsample of men (n = 589) who had peripheral quantitative computed tomography (pQCT) performed at the distal (4%) and mid-shaft (50%) radius. Estimated parameters were total and trabecular vBMD (mg/mm(3)) and cross-sectional area (mm(2)) at the 4% site and cortical vBMD (mg/mm(3)); total, cortical, and medullary area (mm(2)); cortical thickness (mm); and stress strain index (SSI) (mm(3)) at the 50% site. We identified 12 OPG SNPs associated with vBMD and/or geometric parameters, including rs10505348 associated with total vBMD (β [95% CI] = 9.35 [2.12-16.58], P = 0.011), cortical vBMD (β [95% CI] = 5.62 [2.10-9.14], P = 0.002), cortical thickness (β [95% CI] = 0.08 [0.03-0.13], P = 0.002), and medullary area (β [95% CI] = -2.90 [-4.94 to -0.86], P = 0.005) and rs2073618 associated with cortical vBMD (β [95% CI] = -4.30 [-7.78 to -0.82], P = 0.015) and cortical thickness (β [95% CI] = -0.08 [-0.13 to -0.03], P = 0.001). Three RANK SNPs were associated with vBMD, including rs12956925 associated with trabecular vBMD (β [95% CI] = -7.58 [-14.01 to -1.15], P = 0.021). There were five RANK SNPs associated with geometric parameters, including rs8083511 associated with distal radius cross-sectional area (β [95% CI] = 8.90 [0.92-16.88], P = 0.029). No significant association was observed between RANKL SNPs and pQCT parameters. Our findings suggest that genetic variation in OPG and RANK influences radius vBMD and geometry in men.

Stronger bone correlates with African admixture in African-American women

Osteoporosis affects all populations, but the risk for low bone density and fracture varies greatly by self-reported race and ethnicity. In this article, the relationship between measured percent African admixture and hip structural geometry, estimated from the hip structural analysis (HSA) program, was examined in a subcohort of the Women's Health Initiative (WHI). The study sample included 793 African-American women and 8559 non-Hispanic white women. All the participants were postmenopausal, between the ages of 50 and 79 years, at the time of recruitment and were followed for up to 9 years. Bone density and hip geometry were assessed using dual-energy X-ray absorptiometry. African admixture was measured for African Americans using genetic ancestry informative markers. Multiple regression and mixed-effects models were used for cross-sectional and longitudinal analyses, respectively. Covariates assessed from questionnaires and physical measurements were included in the analysis to control for possible confounding effects. The study results show significant correlations between percent of African admixture and HSA assessments. In comparison with non-Hispanic white women, significantly greater bone strength, as indicated by higher hip bone mineral density and stronger hip geometry, in women with higher African admixture was observed. However, women with higher percent African admixture had larger reductions in bone strength than non-Hispanic white women during the follow-up.

The genetics of bone loss: challenges and prospects

CONTEXT

A strong genetic influence on bone mineral density has been long established, and modern genotyping technologies have generated a flurry of new discoveries about the genetic determinants of bone mineral density (BMD) measured at a single time point. However, much less is known about the genetics of age-related bone loss. Identifying bone loss-related genes may provide new routes for therapeutic intervention and osteoporosis prevention.

EVIDENCE ACQUISITION

A review of published peer-reviewed literature on the genetics of bone loss was performed. Relevant studies were summarized, most of which were drawn from the period 1990-2010.

EVIDENCE SYNTHESIS

Although bone loss is a challenging phenotype, available evidence supports a substantial genetic contribution. Some of the genes identified from recent genome-wide association studies of cross-sectional BMD are attractive candidate genes for bone loss, most notably genes in the nuclear factor κB and estrogen endocrine pathways. New insights into the biology of skeletal development and regulation of bone turnover have inspired new hypotheses about genetic regulation of bone loss and may provide new directions for identifying genes associated with bone loss.

CONCLUSIONS

Although recent genome-wide association and candidate gene studies have begun to identify genes that influence BMD, efforts to identify susceptibility genes specific for bone loss have proceeded more slowly. Nevertheless, clues are beginning to emerge on where to look, and as population studies accumulate, there is hope that important bone loss susceptibility genes will soon be identified.

Influence of age and sex steroids on bone density and geometry in middle-aged and elderly European men

SUMMARY

The influence of age and sex steroids on bone density and geometry of the radius was examined in two European Caucasian populations. Age-related change in bone density and geometry was observed. In older men, bioavailable oestradiol may play a role in the maintenance of cortical and trabecular bone mineral density (BMD).

INTRODUCTION

To examine the effect of age and sex steroids on bone density and geometry of the radius in two European Caucasian populations.

METHODS

European Caucasian men aged 40-79 years were recruited from population registers in two centres: Manchester (UK) and Leuven (Belgium), for participation in the European Male Ageing Study. Total testosterone (T) and oestradiol (E(2)) were measured by mass spectrometry and the free and bioavailable fractions calculated. Peripheral quantitative computed tomography was used to scan the radius at distal (4%) and midshaft (50%) sites.

RESULTS

Three hundred thirty-nine men from Manchester and 389 from Leuven, mean ages 60.2 and 60.0 years, respectively, participated. At the 50% radius site, there was a significant decrease with age in cortical BMD, bone mineral content (BMC), cortical thickness, and muscle area, whilst medullary area increased. At the 4% radius site, trabecular and total volumetric BMD declined with age. Increasing bioavailable E(2) (bioE(2)) was associated with increased cortical BMD (50% radius site) and trabecular BMD (4% radius site) in Leuven, but not Manchester, men. This effect was predominantly in those aged 60 years and over. In older Leuven men, bioavailable testosterone (Bio T) was linked with increased cortical BMC, muscle area and SSI (50% radius site) and total area (4% radius site).

CONCLUSIONS

There is age-related change in bone density and geometry at the midshaft radius in middle-aged and elderly European men. In older men bioE(2) may maintain cortical and trabecular BMD. BioT may influence bone health through associations with muscle mass and bone area.

Genetic analysis of vertebral trabecular bone density and cross-sectional area in older men

We investigated 383 bone candidate genes for associations between single nucleotide polymorphisms and vertebral trabecular volumetric bone mineral density (vBMD) and cross-sectional area (CSA) in 2,018 Caucasian men aged ≥ 65 years. SNPs in TGFBR3, SOST, KL, CALCR, LEP, CSF1R, PTN, GNRH2, FGFR2, and MEPE were associated with vBMD and SNPs in CYP11B1, DVL2, DLX5, WNT4, and PAX7 were associated with CSA in independent study samples (p < 0.005).

INRODUCTION

Vertebral bone mineral density and cross-sectional area are important determinants of vertebral bone strength. Little is known about the specific genetic variants that influence these phenotypes in humans.

METHODS

We investigated the potential genetic variants associated with vertebral trabecular volumetric BMD and CSA measured by quantitative computed tomography. We initially tested for association between these phenotypes and 4608 tagging and potentially functional single nucleotide polymorphisms (SNPs) in 383 candidate genes in 862 community-dwelling Caucasian men aged ≥ 65 years in the Osteoporotic Fractures in Men Study.

RESULTS

SNP associations were then validated by genotyping an additional 1,156 randomly sampled men from the same cohort. We identified 11 SNPs in 10 genes (TGFBR3, SOST, KL, CALCR, LEP, CSF1R, PTN, GNRH2, FGFR2, and MEPE) that were consistently associated with trabecular vBMD and five SNPs in five genes (CYP11B1, DVL2, DLX5, WNT4, and PAX7) that were consistently associated with CSA in both samples (p < 0.005).

CONCLUSION

None of the SNPs associated with trabecular vBMD were associated with CSA. Our findings raise the possibility that at least some of the loci for vertebral trabecular BMD and bone size may be distinct.

Bone mass and bone size in pre- or early pubertal 10-year-old black and white South African children and their parents

Genetic factors are thought to maintain bone mass in socioeconomically disadvantaged black South Africans. We compared bone mass between environmentally disadvantaged black and advantaged white children and their parents, after determining the most appropriate method by which to correct bone mineral content (BMC) for size. We collected data from 419 healthy black and white children of mean age 10.6 years (range 10.0-10.9), 406 biological mothers, and 100 biological fathers. Whole-body, femoral neck, lumbar spine, and mid- and distal one-third of radius bone area (BA) and BMC were measured by dual-energy X-ray absorptiometry. Power coefficients (PCs) were calculated from the linear-regression analyses of ln(BMC) on ln(BA) and used to correct site-specific BMC for bone size differences. Heritability (½h(2), %) by maternal and paternal descent was estimated by regressing children's Z scores on parents' Z scores. Correcting BMC for height, weight, and BA(PC) accounted for the greatest variance of BMC at all skeletal sites. In so doing, BMC in blacks was up to 2.6 times greater at the femoral neck and lumbar spine. Maternal and paternal heritability was estimated to be ~30% in both black and white subjects. These results may in part explain the lower prevalence of fragility fractures at the hip in black South African children when compared to whites. Heritability was comparable between environmentally disadvantaged black and advantaged white South African children and similar to that reported for Caucasians in other parts of the world.

VKORC1 common variation and bone mineral density in the Third National Health and Nutrition Examination Survey

Osteoporosis, defined by low bone mineral density (BMD), is common among postmenopausal women. The distribution of BMD varies across populations and is shaped by both environmental and genetic factors. Because the candidate gene vitamin K epoxide reductase complex subunit 1 (VKORC1) generates vitamin K quinone, a cofactor for the gamma-carboxylation of bone-related proteins such as osteocalcin, we hypothesized that VKORC1 genetic variants may be associated with BMD and osteoporosis in the general population. To test this hypothesis, we genotyped six VKORC1 SNPs in 7,159 individuals from the Third National Health and Nutrition Examination Survey (NHANES III). NHANES III is a nationally representative sample linked to health and lifestyle variables including BMD, which was measured using dual energy x-ray absorptiometry (DEXA) on four regions of the proximal femur. In adjusted models stratified by race/ethnicity and sex, SNPs rs9923231 and rs9934438 were associated with increased BMD (p = 0.039 and 0.024, respectively) while rs8050894 was associated with decreased BMD (p = 0.016) among non-Hispanic black males (n = 619). VKORC1 rs2884737 was associated with decreased BMD among Mexican-American males (n = 795; p = 0.004). We then tested for associations between VKORC1 SNPs and osteoporosis, but the results did not mirror the associations observed between VKORC1 and BMD, possibly due to small numbers of cases. This is the first report of VKORC1 common genetic variation associated with BMD, and one of the few reports available that investigate the genetics of BMD and osteoporosis in diverse populations.

Muscle power and physical activity are associated with bone strength in older men: The osteoporotic fractures in men study

The purpose of these analyses was to explore whether physical activity score, leg power or grip strength were associated with tibia and radius estimates of bone strength, cortical density, or total bone area. Peripheral quantitative computed tomography (pQCT) was used to compare tibial and radial bone volumetric density (vBMD, mg/cm(3)), total (ToA, mm(2)) and cortical (CoA, mm(2)) bone area, and estimates of bone compressive strength (bone strength index, BSI) and bending strength (polar strength strain index, SSIp) in a subset (n=1171) of men (> or = 65 years) who participated in the multi-site Osteoporotic Fractures in Men (MrOS) study. Physical activity was assessed by questionnaire (PASE), leg power by Nottingham Power Rig, and grip strength by a hand-held Dynamometer. Participants were categorized into quartiles of PASE, grip strength or leg power. The model was adjusted for age, race, clinic, weight, and limb length. In the tibia, BSI (+7%) and SSIp (+4%) were highest in the most active physically quartile compared to the least active (p<0.05). At the 4% site of the tibia, men with the greatest leg power had both greater ToA (+5%, p<0.001) and BSI (+5.3%, p=0.086) compared to men with the least leg power. At the 66% site of the tibia, the men with the highest leg power, compared to the men with the lowest leg power, had greater ToA (+3%, p=0.045) SSIp (+5%, p=0.008). Similar results were found at both the distal and midshaft of the radius. The findings of this study suggest the importance of maintaining levels of physical activity and muscle strength in older men to prevent bone fragility.

Influence of heredity and environment on peak bone density: a parent-offspring study

The aim of the study was to determine the relative influence of heredity and environment on peak bone density and also to estimate the risk of having low peak bone density if the bone density of parents is low. The study comprised 83 families (48 daughters and 35 sons and their parents). The children were at an age when bone density is at its peak at most skeletal sites (22.2+/-1.8 girls; 23.1+/-1.2 boys). Bone mineral density (BMD; g/cm(2)) was determined by dual-energy X-ray absorptiometry. Anthropometric measurements were made, and calcium intake and physical activity were assessed. Heredity accounted for 22-42% of the variation in BMD of the children, depending on the skeletal site. Heritability for cortical BMD of mid-radius was considerably lower than that for spinal trabecular BMD. Children whose parents had low BMDs (T-score< or =-1) were 1.1 times more likely to inherit low BMD. Child BMD depended significantly on parent BMD and also on physical activity. In our study, heredity accounted for the total BMD variation more than the environmental factors. This influence was lower in the cortical than in the trabecular parts of the skeleton. Optimal environmental factors, such as physical activity, may influence the risk of inheriting low BMD.

Rate of bone loss is greater in young Mexican American men than women: the San Antonio Family Osteoporosis Study

Little is known about the progression of bone loss during young adulthood and whether it differs between men and women. As part of the San Antonio Family Osteoporosis Study we tested whether bone mineral density (BMD) changed over time in men or women, and whether the rate of BMD change differed between the sexes. BMD of the proximal femur, spine, radius, and whole body was measured in 115 men and 202 pre-menopausal women (ages 25 to 45 years; Mexican American ancestry) by dual-energy x-ray absorptiometry at two time points (5.6 years apart), from which annual percent change-in-BMD was calculated. Likelihood-based methods were used to test whether change-in-BMD differs from zero or differs between men and women. In men, percent change-in-BMD was significantly greater than zero for the 1/3 radius (i.e. indicating a gain of BMD; Bonferroni-adjusted p<0.01), less than zero for the femoral neck, lumbar spine, ultradistal radius, and whole body (i.e. indicating a loss of BMD; p<0.01 for all), and not different than zero for the total hip (p=0.24). In women, percent change-in-BMD was greater than zero for the total hip, 1/3 radius, and whole body (p<0.01 for all), less than zero for the ultradistal radius (p<0.01), and not significantly different than zero for the femoral neck and lumbar spine (p=1.0 for both). For all skeletal sites, men experienced greater decrease in BMD (or less increase in BMD) than women; this result was observed both with and without adjustment for age, BMI, and change-in-BMI (p<0.05 for all). These results suggest that significant bone loss occurs at some skeletal sites in young men and women, and that loss of BMD is occurring significantly faster, or gain of BMD is occurring significantly slower, in young men compared to young women.

Genome-wide pleiotropy of osteoporosis-related phenotypes: the Framingham Study

Genome-wide association studies offer an unbiased approach to identify new candidate genes for osteoporosis. We examined the Affymetrix 500K + 50K SNP GeneChip marker sets for associations with multiple osteoporosis-related traits at various skeletal sites, including bone mineral density (BMD, hip and spine), heel ultrasound, and hip geometric indices in the Framingham Osteoporosis Study. We evaluated 433,510 single-nucleotide polymorphisms (SNPs) in 2073 women (mean age 65 years), members of two-generational families. Variance components analysis was performed to estimate phenotypic, genetic, and environmental correlations (rho(P), rho(G), and rho(E)) among bone traits. Linear mixed-effects models were used to test associations between SNPs and multivariable-adjusted trait values. We evaluated the proportion of SNPs associated with pairs of the traits at a nominal significance threshold alpha = 0.01. We found substantial correlation between the proportion of associated SNPs and the rho(P) and rho(G) (r = 0.91 and 0.84, respectively) but much lower with rho(E) (r = 0.38). Thus, for example, hip and spine BMD had 6.8% associated SNPs in common, corresponding to rho(P) = 0.55 and rho(G) = 0.66 between them. Fewer SNPs were associated with both BMD and any of the hip geometric traits (eg, femoral neck and shaft width, section moduli, neck shaft angle, and neck length); rho(G) between BMD and geometric traits ranged from -0.24 to +0.40. In conclusion, we examined relationships between osteoporosis-related traits based on genome-wide associations. Most of the similarity between the quantitative bone phenotypes may be attributed to pleiotropic effects of genes. This knowledge may prove helpful in defining the best phenotypes to be used in genetic studies of osteoporosis.

Candidate gene analysis of femoral neck trabecular and cortical volumetric bone mineral density in older men

In contrast to conventional dual-energy X-ray absorptiometry, quantitative computed tomography separately measures trabecular and cortical volumetric bone mineral density (vBMD). Little is known about the genetic variants associated with trabecular and cortical vBMD in humans, although both may be important for determining bone strength and osteoporotic risk. In the current analysis, we tested the hypothesis that there are genetic variants associated with trabecular and cortical vBMD at the femoral neck by genotyping 4608 tagging and potentially functional single-nucleotide polymorphisms (SNPs) in 383 bone metabolism candidate genes in 822 Caucasian men aged 65 years or older from the Osteoporotic Fractures in Men Study (MrOS). Promising SNP associations then were tested for replication in an additional 1155 men from the same study. We identified SNPs in five genes (IFNAR2, NFATC1, SMAD1, HOXA, and KLF10) that were robustly associated with cortical vBMD and SNPs in nine genes (APC, ATF2, BMP3, BMP7, FGF18, FLT1, TGFB3, THRB, and RUNX1) that were robustly associated with trabecular vBMD. There was no overlap between genes associated with cortical vBMD and trabecular vBMD. These findings identify novel genetic variants for cortical and trabecular vBMD and raise the possibility that some genetic loci may be unique for each bone compartment.

High-density association study of 383 candidate genes for volumetric BMD at the femoral neck and lumbar spine among older men

Genetics is a well-established but poorly understood determinant of BMD. Whereas some genetic variants may influence BMD throughout the body, others may be skeletal site specific. We initially screened for associations between 4608 tagging and potentially functional single nucleotide polymorphisms (SNPs) in 383 candidate genes and femoral neck and lumbar spine volumetric BMD (vBMD) measured from QCT scans among 862 community-dwelling white men >or=65 yr of age in the Osteoporotic Fractures in Men Study (MrOS). The most promising SNP associations (p < 0.01) were validated by genotyping an additional 1156 white men from MrOS. This analysis identified 8 SNPs in 6 genes (APC, DMP1, FGFR2, FLT1, HOXA, and PTN) that were associated with femoral neck vBMD and 13 SNPs in 7 genes (APC, BMPR1B, FOXC2, HOXA, IGFBP2, NFATC1, and SOST) that were associated with lumbar spine vBMD in both genotyping samples (p < 0.05). Although most associations were specific to one skeletal site, SNPs in the APC and HOXA gene regions were associated with both femoral neck and lumbar spine BMD. This analysis identifies several novel and robust genetic associations for volumetric BMD, and these findings in combination with other data suggest the presence of genetic loci for volumetric BMD that are at least to some extent skeletal-site specific.

A comparison of principal component analysis and factor analysis strategies for uncovering pleiotropic factors

Principal component analysis (PCA) and factor analysis (FA) are often used to uncover genetic factors that contribute to complex disease phenotypes. The purpose of such an analysis is to distill a genetic signal from a large number of correlated phenotype measurements. That signal can then be used in genetic analyses (e.g. linkage analysis), presumably leading to greater success at finding genes than one would achieve with any one raw trait. Although both PCA and FA have been used this way, there has been no comparison of their performance in the literature. We compared the ability of these two procedures to extract unobserved underlying genetic components from complex simulated data on nuclear families. We first simulated seven underlying genetic and environmentally determined traits. Then we derived two sets of 50 complex (observed) traits using algebraic combinations of the underlying components. We next performed PCA and FA on the complex traits. We assessed two aspects of the performance of the methods: (1) ability to detect the underlying genetic components; (2) whether the methods worked better when applied to raw traits or to residuals (after regressing out significant environmental covariates). Our results indicate that both the methods behave similarly in most cases, although FA generally produced factors that had stronger correlations with the underlying traits. We also found that using residuals in PCA or FA analyses greatly increased the probability that the PCs or factors detected common genetic components instead of common environmental factors, except if there was statistical interaction between genetic and environmental factors.

Association analysis of WNT10B with bone mass and structure among individuals of African ancestry

Wnts comprise a family of secreted growth factors that regulate the development and maintenance of many organs. Recently, Wnt10b was shown to stimulate osteoblastogenesis and bone formation in mice. To evaluate further the role of Wnt10b in bone health in humans, we performed bidirectional sequencing of approximately 8 kb of the WNT10B gene region in 192 individuals (96 African, 96 white) to identify single nucleotide polymorphisms (SNPs). We identified 19 SNPs with minor allele frequency (MAF) > or =0.01. Ten of these SNPs were not present in the NCBI dbSNP database (build 127), whereas 10 of the 20 SNPs (50%) reported in dbSNP were not verified. We initially genotyped seven tagging SNPs that captured common (MAF > or = 0.05) variation in the region with r (2) > 0.80 and a potentially functional SNP in exon 5 in 1035 Afro-Caribbean men > or =40 yr of age. Association analysis showed three SNPs in a 3' region of linkage disequilibrium that were associated with DXA measures of hip BMD. Associations between two of these three SNPs (rs1051886, rs3741627) with hip BMD were replicated in an additional 980 Afro-Caribbean men (p < 0.05), in the combined sample of 2015 men (p < or = 0.006), and in 416 individuals > or =18 yr of age (mean, 44 yr) belonging to eight extended, multigenerational Afro-Caribbean families with mean family size >50 (3535 relative pairs; p < 0.05). Further analysis showed that rs1051886 and rs3741627 were associated with cortical cross-sectional area, periosteal circumference, and BMC in the radius, such that individuals with the minor alleles had lower biomechanical indices of long-bone bending strength. This analysis implicates the WNT10B locus as a genetic element in the regulation of bone mass and structural geometry.

Quantitative trait locus on chromosome 1q influences bone loss in young Mexican American adults

Bone loss occurs as early as the third decade and its cumulative effect throughout adulthood may impact risk for osteoporosis in later life, however, the genes and environmental factors influencing early bone loss are largely unknown. We investigated the role of genes in the change in bone mineral density (BMD) in participants in the San Antonio Family Osteoporosis Study. BMD change in 327 Mexican Americans (ages 25-45 years) from 32 extended pedigrees was calculated from DXA measurements at baseline and follow-up (3.5 to 8.9 years later). Family-based likelihood methods were used to estimate heritability (h(2)) and perform autosome-wide linkage analysis for BMD change of the proximal femur and forearm and to estimate heritability for BMD change of lumbar spine. BMD change was significantly heritable for total hip, ultradistal radius, and 33% radius (h(2) = 0.34, 0.34, and 0.27, respectively; p < 0.03 for all), modestly heritable for femoral neck (h(2) = 0.22; p = 0.06) and not heritable for spine BMD. Covariates associated with BMD change included age, sex, baseline BMD, menopause, body mass index, and interim BMI change, and accounted for 6% to 24% of phenotype variation. A significant quantitative trait locus (LOD = 3.6) for femoral neck BMD change was observed on chromosome 1q23. In conclusion, we observed that change in BMD in young adults is heritable and performed one of the first linkage studies for BMD change. Linkage to chromosome 1q23 suggests that this region may harbor one or more genes involved in regulating early BMD change of the femoral neck.

Genetic influences on bone loss in the San Antonio Family Osteoporosis study

The genetic contribution to age-related bone loss is not well understood. We estimated that genes accounted for 25-45% of variation in 5-year change in bone mineral density in men and women. An autosome-wide linkage scan yielded no significant evidence for chromosomal regions implicated in bone loss.

INTRODUCTION

The contribution of genetics to acquisition of peak bone mass is well documented, but little is known about the influence of genes on subsequent bone loss with age. We therefore measured 5-year change in bone mineral density (BMD) in 300 Mexican Americans (>45 years of age) from the San Antonio Family Osteoporosis Study to identify genetic factors influencing bone loss.

METHODS

Annualized change in BMD was calculated from measurements taken 5.5 years apart. Heritability (h(2)) of BMD change was estimated using variance components methods and autosome-wide linkage analysis was carried out using 460 microsatellite markers at a mean 7.6 cM interval density.

RESULTS

Rate of BMD change was heritable at the forearm (h(2) = 0.31, p = 0.021), hip (h(2) = 0.44, p = 0.017), spine (h(2) = 0.42, p = 0.005), but not whole body (h(2) = 0.18, p = 0.123). Covariates associated with rapid bone loss (advanced age, baseline BMD, female sex, low baseline weight, postmenopausal status, and interim weight loss) accounted for 10% to 28% of trait variation. No significant evidence of linkage was observed at any skeletal site.

CONCLUSIONS

This is one of the first studies to report significant heritability of BMD change for weight-bearing and non-weight-bearing bones in an unselected population and the first linkage scan for change in BMD.

Genetics of osteoporosis

Osteoporosis is a frequent skeletal disorder, particularly among postmenopausal women. It affects approximately 30% of women and 12% of men above 50 years of age. It is characterized by reduced bone mass and alterations in bone microarchitecture that result in impaired bone strength and a propensity to fracture. Decreased bone mass is the consequence of an imbalance in the bone remodeling process, resulting from complex interactions between acquired and genetic factors. The former include physical activity, nutrition and other lifestyle habits, as well as the skeletal effects of some diseases and drug therapies. Genetic factors have been extensively studied during the past 15 years. We will review some important studies that exemplify the advances and the difficulties in this research field.

Correlates of bone mineral density among postmenopausal women of African Caribbean ancestry: Tobago women's health study

Population dynamics predict a drastic growth in the number of older minority women, and resultant increases in the number of fractures. Low bone mineral density (BMD) is an important risk factor for fracture. Many studies have identified the lifestyle and health-related factors that correlate with BMD in Whites. Few studies have focused on non-Whites. The objective of the current analyses is to examine the lifestyle, anthropometric and health-related factors that are correlated with BMD in a population based cohort of Caribbean women of West African ancestry. We enrolled 340 postmenopausal women residing on the Caribbean Island of Tobago. Participants completed a questionnaire and had anthropometric measures taken. Hip BMD was measured by DXA. We estimated volumetric BMD by calculating bone mineral apparent density (BMAD). BMD was >10% and >25% higher across all age groups in Tobagonian women compared to US non-Hispanic Black and White women, respectively. In multiple linear regression models, 35-36% of the variability in femoral neck and total hip BMD respectively was predicted. Each 16-kg (one standard deviation (SD)) increase in weight was associated with 5% higher BMD; and weight explained over 10% of the variability of BMD. Each 8-year (1 SD) increase in age was associated with 5% lower BMD. Current use of both thiazide diuretics and oral hypoglycemic medication were associated with 4-5% higher BMD. For femoral neck BMAD, 26% of the variability was explained by a multiple linear regression model. Current statin use was associated with 5% higher BMAD and a history of breast feeding or coronary heart disease was associated with 1-1.5% of higher BMAD. In conclusion, African Caribbean women have the highest BMD on a population level reported to date for women. This may reflect low European admixture. Correlates of BMD among Caribbean women of West African ancestry were similar to those reported for U.S. Black and White women.

Implementing an intervention to improve bone mineral density in survivors of childhood acute lymphoblastic leukemia: BONEII, a prospective placebo-controlled double-blind randomized interventional longitudinal study design

The BONEII study is a large two-phase study. The baseline study (Study 1) aims to estimate the prevalence of diminished bone mineral density (BMD) in patients treated for childhood acute lymphoblastic leukemia (ALL) and identify risk factors for BMD deficits. The interventional phase (Study 2) of BONEII has a placebo-controlled double-blind randomized longitudinal design to evaluate the effects of nutritional counseling and calcium and vitamin D supplementation on changes in BMD and serum and urine markers of bone metabolism. The extensive information being collected through this large study will serve as a repository of relational data about BMD and bone turnover and will support further investigations to assess the association of calcium metabolism, bone turnover, nutritional intake, lifestyle factors (such as exercise and the use of alcohol and tobacco), and the specific agents used in ALL therapy in this rapidly increasing population of childhood cancer survivors.

Pleiotropy and heterogeneity in the expression of bone strength-related phenotypes in extended pedigrees

Genetic analysis in 3,535 relative pairs from extended multigenerational families of African heritage showed that volumetric BMD is a highly heritable polygenic trait that is under compartment-specific genetic regulation. The majority of the phenotypic variation in bone size and volumetric BMD also seems to be strongly influenced by distinct genes for each trait.

INTRODUCTION

BMD and bone size contribute to bone strength and the risk of fracture. Little is known about the genetic architecture of QCT measures of volumetric BMD and bone size. We studied the contribution of genes, shared genes (pleiotropy), and shared environment to cortical and trabecular volumetric BMD and bone size using variance components analysis.

MATERIALS AND METHODS

A total of 471 individuals >or=18 yr of age (mean, 43 yr) from eight multigenerational Afro-Caribbean families (mean family size > 50; 3535 relative pairs) underwent a peripheral QCT scan of the radius and tibia and anthropometry.

RESULTS

Strong positive genetic correlations were observed for trabecular or cortical BMD measured at the tibia and radius (rho(G) > 0.82, p < 0.01), but not between trabecular and cortical BMD measured within the same anatomical site. Genetic correlations between volumetric BMD and bone length and circumference were also not statistically significant.

CONCLUSIONS

BMD is a highly heritable polygenic trait that is under compartment-specific genetic regulation. The majority of the phenotypic variation in skeletal size and density seems to be strongly influenced by distinct sets of genes for each trait.