The heritability of bone mineral density, ultrasound of the calcaneus and hip axis length: a study of postmenopausal twins

Population based studies have demonstrated that having a first degree relative with a hip fracture is predictive of future hip fractures. Postmenopausal bone mineral density (BMD), ultrasound of calcaneus and hip axis length are associated with hip fracture, with the association for ultrasound and hip axis length being independent of BMD. The aim of this study was to determine the genetic component of these three important risk factors. We performed a classical twin study using 500 normal female twins, 128 identical and 122 non-identical pairs, aged 50 to 70 years. We measured bone mineral density at multiple sites, hip axis length (distance from the inner rim of the acetabulum to the greater trochanter), broadband ultrasound attenuation and velocity of sound of the calcaneus. Bone density had a strong genetic component at all sites with estimates of heritability ranging from 0.46 to 0.84. Hip axis length and velocity of sound had major genetic components with estimates of 0.62 and 0.61 respectively, which remained virtually unchanged after adjustment for bone mineral density. Broadband ultrasound attenuation had a moderate genetic component with an estimate of 0.53, which was reduced further to 0.45 after adjustment for BMD. In summary, all three bone measurements, which are independently associated with hip fracture, are independently heritable. This study suggests that a combination of different genetic factors acting on the structure, dimensions and density of bone may explain the importance of family history as a risk factor for hip fracture.

Cardiovascular diseases and risk of hip fracture

CONTEXT

Recent studies indicate common etiologies for cardiovascular disease (CVD) and osteoporotic fractures.

OBJECTIVES

To examine the relation between CVD and risk of hip fracture in twins and evaluate the relative importance of genetics and lifestyle factors in this association.

DESIGN, SETTING, AND PARTICIPANTS

A cohort of all 31,936 Swedish twins born from 1914-1944 was followed up from the age of 50 years. The National Patient Registry identified twins with CVDs and fractures from 1964 through 2005. Time-dependent exposures using Cox proportional hazard regression models were evaluated.

MAIN OUTCOME MEASURE

Time to hip fracture after diagnosis of CVD.

RESULTS

The crude absolute rate of hip fractures was 12.6 per 1000 person-years after a diagnosis of heart failure, 12.6 per 1000 person-years after a stroke, 6.6 per 1000 person-years after a diagnosis of peripheral atherosclerosis, and 5.2 per 1000 person-years after a diagnosis of ischemic heart disease compared with 1.2 per 1000 person-years for those without a CVD diagnosis. The multivariable-adjusted hazard ratio (HR) of hip fracture after a diagnosis of heart failure was 4.40 (95% confidence interval [CI], 3.43-5.63); after a stroke, the HR was 5.09 (95% CI, 4.18-6.20); after a diagnosis of peripheral atherosclerosis, the HR was 3.20 (95% CI, 2.28-4.50); and after an ischemic heart disease event, the HR was 2.32 (95% CI, 1.91-2.84). Identical twins without heart failure and stroke also had, after their co-twins had been exposed to these respective diseases, an increased rate of hip fracture. These sibling twins pseudoexposed for heart failure had a multivariable-adjusted HR of 3.74 (95% CI, 1.97-7.10) for hip fracture, whereas pseudoexposure for stroke had an HR of 2.29 (95% CI, 1.20-4.35).

CONCLUSIONS

A diagnosis of CVD was significantly associated with risk of subsequent hip fracture. Increased risks in co-twins without an index diagnosis suggest genetic factors in the association between CVD and osteoporotic fractures.

A family history of fracture and fracture risk: a meta-analysis

The aims of the present study were to determine whether a parental history of any fracture or hip fracture specifically are significant risk factors for future fracture in an international setting, and to explore the effects of age, sex and bone mineral density (BMD) on this risk. We studied 34,928 men and women from seven prospectively studied cohorts followed for 134,374 person-years. The cohorts comprised the EPOS/EVOS study, CaMos, the Rotterdam Study, DOES and cohorts at Sheffield, Rochester and Gothenburg. The effect of family history of osteoporotic fracture or of hip fracture in first-degree relatives, BMD and age on all clinical fracture, osteoporotic fracture and hip fracture risk alone was examined using Poisson regression in each cohort and for each sex. The results of the different studies were merged from the weighted beta coefficients. A parental history of fracture was associated with a modest but significantly increased risk of any fracture, osteoporotic fracture and hip fracture in men and women combined. The risk ratio (RR) for any fracture was 1.17 (95% CI=1.07-1.28), for any osteoporotic fracture was 1.18 (95% CI=1.06-1.31), and for hip fracture was 1.49 (95% CI=1.17-1.89). The risk ratio was higher at younger ages but not significantly so. No significant difference in risk was seen between men and women with a parental history for any fracture (RR=1.17 and 1.17, respectively) or for an osteoporotic fracture (RR=1.17 and 1.18, respectively). For hip fracture, the risk ratios were somewhat higher, but not significantly higher, in men than in women (RR=2.02 and 1.38, respectively). A family history of hip fracture in parents was associated with a significant risk both of all osteoporotic fracture (RR 1.54; 95CI=1.25-1.88) and of hip fracture (RR=2.27; 95% CI=1.47-3.49). The risk was not significantly changed when BMD was added to the model. We conclude that a parental history of fracture (particularly a family history of hip fracture) confers an increased risk of fracture that is independent of BMD. Its identification on an international basis supports the use of this risk factor in case-finding strategies.

Genetic Liability to Fractures in the Elderly

BACKGROUND

The genetic impact on the causation of osteoporotic fractures is unclear. A large twin study is ideally suited to determine the genetic liability to categories of fracture at various ages.

METHODS

A cohort of all 33 432 Swedish twins born from 1896 to 1944 was used to evaluate the genetic liability to fracture occurrence in the elderly. The Swedish Inpatient Registry and computer-assisted telephone interviews enabled us to identify 6021 twins with any fracture, 3599 with an osteoporotic fracture, and 1055 with a hip fracture after the age of 50 years.

RESULTS

Genetic variation in liability to fracture differed considerably by type of fracture and age. Less than 20% of the overall age-adjusted fracture variance was explained by genetic variation. The age-adjusted heritability of any osteoporotic fracture was slightly greater (0.27; 95% confidence interval [CI], 0.09-0.28), and for hip fracture alone, it was 0.48 (95% CI, 0.28-0.57). Heritability was not attenuated after further adjustment for several known osteoporotic covariates but was considerably greater for first hip fractures before the age of 69 years (0.68; 95% CI, 0.41-0.78) and between 69 and 79 years (0.47; 95% CI, 0.04-0.62) than for hip fractures after 79 years of age (0.03; 95% CI, 0.00-0.26).

CONCLUSIONS

The importance of genetic factors in propensity to fractures depends on fracture site and age. The search for susceptibility genes and environmental factors that may modulate expression of these genes in younger elderly patients with hip fracture, the most devastating osteoporotic fracture, should be encouraged. Prevention of fractures in the oldest elderly should focus on lifestyle interventions.

Plasma homocysteine, folate, and vitamin B 12 and the risk of hip fracture: the hordaland homocysteine study

Homocysteine and related factors were evaluated as risk factors for subsequent hip fractures among 4766 elderly men and women. High levels of homocysteine and low levels of folate predicted fracture, whereas vitamin B12 and genotypes were not related to fracture risk. High homocysteine may be a modifiable risk factor for hip fracture.

INTRODUCTION

Elevated plasma total homocysteine (tHcy) and deficiencies of folate and vitamin B12 are associated with risk of osteoporosis and fracture. We examined whether plasma levels of tHcy, folate, and vitamin B12 and the methylenetetrahydrofolate reductase (MTHFR) 677C-->T and 1298C-->T polymorphisms predicted hip fracture.

MATERIALS AND METHODS

This was a population-based prospective study of 2639 women and 2127 men who were 65-67 yr at enrollment in 1992-1993. Information on hip fracture was obtained from computerized records of discharge diagnoses from all hospitalizations in the region in the period between enrollment and November 30, 2005. Cox proportional hazard regression was used to estimate fracture risk according to levels of plasma tHcy, folate, and vitamin B12 and for different genotypes.

RESULTS

Over a median follow-up period of 12.6 yr, hip fracture was recorded in 184 (7.0%) women and 90 (4.2%) men. The adjusted hazard ratio (95% CI) for fracture in subjects with high (>or=15 microM) compared with low levels (<9.0 microM) of tHcy was 2.42 (1.43-4.09) among women and 1.37 (0.63-2.98) among men. Dose-response analyses indicated a positive association between plasma tHcy and risk of fracture in both sexes and a negative association between plasma folate and risk of fracture among women only. Plasma vitamin B12 level or MTHFR genotype was not significantly related to risk of fracture after adjustments for confounding factors. The association between tHcy and risk of hip fracture was only slightly weakened by adjustments for plasma levels of vitamin B12 and folate.

CONCLUSIONS

tHcy seems to be a predictor for hip fracture among elderly men and women. Folate was a predictor among women only, whereas vitamin B12 and MTHFR genotype did not predict hip fracture. Our data corroborate the hypothesis that homocysteine may play a role in the pathogenesis of osteoporotic fractures.

Apolipoprotein E polymorphism: A new genetic marker of hip fracture risk--The Study of Osteoporotic Fractures

Hip fractures are common and devastating events. The apolipoprotein E*4 (APOE) allele, associated with Alzheimer's disease, has also been associated with osteoporosis in hemodialysis patients. We prospectively studied 1750 women, age >/=65 years, who underwent measurements of hip and calcaneal bone mineral density (BMD), were typed for APOE and followed for approximately 7.0 years for the occurrence of fractures and falls. Women with at least one APOE*4 allele had an increased risk of hip fracture, relative hazard (RH) (95% confidence interval) = 1.90 (1.05-3.41) and wrist fracture, RH = 1.67 (1.01-2.77) compared with women without APOE*4, even after adjusting for age, cognitive function, falling, and BMD. The effect of APOE*4 on hip fracture was greatest among women with additional (>/=3) other risk factors. Women with an APOE*4 allele were also likely to report a maternal history of fracture. The average number of falls per year did not differ by APOE*4: 0.46 for APOE*4 women and 0.41 for women without an APOE*4 allele. Women with an APOE*4 allele experienced greater weight loss which contributed to faster rates of bone loss. We conclude that women with the APOE*4 polymorphism are at substantially increased risk of hip and wrist fracture that is not explained by bone density, impaired cognitive function, or falling. Possible alternate explanations include an effect of APOE on vitamin K, bone turnover, or weight loss. The APOE polymorphism may be a candidate gene for hip fractures among community dwelling nondemented women.

Polymorphisms in the vitamin D receptor gene and bone mass, bone turnover and osteoporotic fractures

BACKGROUND

Vitamin D is essential for normal bone metabolism. Polymorphisms in exon 2, intron 8 and exon 9 of the vitamin D receptor (VDR) gene have previously been found to be associated with bone mass and bone turnover.

MATERIALS AND METHODS

We examined the effect of these polymorphisms, separately and in combination, on bone mineral density (BMD), bone turnover, and the prevalence of osteoporotic fractures in 192 osteoporotic patients and 207 normal controls. The four polymorphisms were determined by RFLP using Fok I (T2-C), Bsm I (intron 8), Apa I (intron 8) and Taq I (T1055-C) after PCR.

RESULTS

We did not find any association between the Fok I polymorphism and bone mass, bone turnover or prevalence of osteoporotic fractures. We found that BB + Bb-genotypes were more frequent in patients with osteoporotic fractures (chi2 = 3.50, P = 0. 06). Furthermore, BMD of the intertrochanteric region (P < 0.0001, ANOVA) as well as the total hip (P < 0.01, ANOVA) were higher in individuals with the bb-genotype. The Apa I and the Taq I polymorphisms were not distributed differently among osteoporotic patients and normal controls. Apa I was not associated with differences in BMD. BMD of the intertrochanteric region was higher in individuals with the TT-genotype compared with individuals with the Tt- or tt-genotypes (P < 0.01, ANOVA), while no differences could be demonstrated in BMD of the lumbar spine, femoral neck, trochanter or Wards triangle. Combining the genotypes generally reflected the differences caused by the Bsm I polymorphism.

CONCLUSION

We have found that the B-allele of the Bsm I polymorphism in the 3' untranslated region of the VDR was associated with low BMD at the hip, and tended to be associated with osteoporotic fractures. The translation initiation polymorphism in the VDR does not affect BMD and is not associated with osteoporotic fractures in men or women.

The genetics of proximal femur geometry, distribution of bone mass and bone mineral density

To estimate genetic effects on femoral neck geometry and the distribution of bone mineral within the proximal femur a cross-sectional twin analysis was carried out at a university hospital that compared correlations in these traits in pairs of mono- and dizygotic female twins. Monozygotic (MZ, n = 51 pairs, age 49.1 +/- 9.3 years) and dizygotic (DZ, n = 26 pairs, age 45.7 +/- 11.3 years) twins were randomly selected from a larger sample of twins previously studied. Measurements of bone mineral density (BMD), femoral neck angles and length, cross-sectional area and moment of interia, the center of mass of the narrowest cross-section of the femoral neck, and BMDs of regions within the femoral neck were made. A summary index of the resistance of the femoral neck to forces experienced in a fall with impact on the greater trochanter (Fall Index, FI) was calculated. MZ pair intraclass correlations (rMZ) were significantly (p < 0.05) different from zero for all bone mass and femoral geometry variables (0.35 < rMZ < 0.82). DZ pair correlations (rDZ) were lower than rMZ for all variables (0.04 < rDZ < 0.52) except femoral neck length (rDZ = 0.38, rMZ = 0.36). After adjustment for BMD of the femoral neck, rMZ was significantly greater than rDZ, yielding high heritability estimates for regional BMDs (0.72 < H2 < 0.78), the center of mass of the femoral neck (H2 = 0.70, -0.04 to 1.43 95% CI) and the resistance of the femoral neck to forces experienced in a fall (FI, H2 = 0.94, 0.06 to 1.85 95% CI), but not for femoral neck length. Adjustments for age did not alter these findings. It is concluded that there are significant familial influences on the distribution of femoral bone mass and on the calculated structural strength of the proximal femur, but not on femoral neck length. If the assumptions of the twin model are correct, this is evidence for genetic factors influencing these traits.

Family history and risk of osteoporotic fracture. Study of Osteoporotic Fractures Research Group

The importance of family history of fractures as a risk factor for fractures is unclear. The aim of this study was to test the hypothesis that family history of fracture increased a woman's risk of hip, wrist and other osteoporotic fracture and determine whether the influence of family history is independent of low bone density. We tested this hypothesis in a prospective study of 9704 Caucasian women, age 65 years or older, by assessing family history and bone density of the radius and calcaneus at baseline; 7963 women had femoral bone density measurements two years later. Fractures occurring during an average of 7.1 years of follow-up since baseline and 5.2 years since the second examination were confirmed by radiographic report. After adjusting for age, risk of hip fracture was increased in those with a maternal (1.48; 95% CI = 1.03-2.11); sister's (1.83; 1.20-2.80) or brother's history of hip fracture (2.26; 1.16-4.42). Risk of wrist fracture was increased by maternal (1.52; 1.10-2.11) and paternal (2.41; 1.14-5.07) history of wrist fracture. Adjustment for bone density did not consistently and substantially affect the strength of the associations. Family history of hip fracture was not associated with an increased risk of wrist fracture and family history of wrist fracture did not increase the risk of hip fracture. We conclude that family history is an important risk factor for fracture that may act, at least in part, through means besides bone density. Furthermore, the effect of family history is not a general but site-specific predisposition to fracture.

GWAS of bone size yields twelve loci that also affect height, BMD, osteoarthritis or fractures

Bone area is one measure of bone size that is easily derived from dual-energy X-ray absorptiometry (DXA) scans. In a GWA study of DXA bone area of the hip and lumbar spine (N ≥ 28,954), we find thirteen independent association signals at twelve loci that replicate in samples of European and East Asian descent (N = 13,608 - 21,277). Eight DXA area loci associate with osteoarthritis, including rs143384 in GDF5 and a missense variant in COL11A1 (rs3753841). The strongest DXA area association is with rs11614913[T] in the microRNA MIR196A2 gene that associates with lumbar spine area (P = 2.3 × 10-42, β = -0.090) and confers risk of hip fracture (P = 1.0 × 10-8, OR = 1.11). We demonstrate that the risk allele is less efficient in repressing miR-196a-5p target genes. We also show that the DXA area measure contributes to the risk of hip fracture independent of bone density.

Alcohol consumption, bone density, and hip fracture among older adults: the cardiovascular health study

INTRODUCTION

Previous studies have found inconsistent relationships of alcohol consumption with risk of hip fracture, and the importance of bone mineral density and risk of falls in mediating such a relationship has not been determined.

METHODS

As part of the Cardiovascular Health Study, a population-based cohort study of adults aged 65 years and older from four U.S. communities, 5,865 participants reported their use of beer, wine, and liquor yearly. We identified cases of hip fracture unrelated to malignancy or motor vehicle accidents using hospitalization discharge diagnoses. A subgroup of 1,567 participants in two communities underwent dual-energy x-ray absorptiometry scans to assess bone mineral density.

RESULTS

A total of 412 cases of hip fracture occurred during an average of 12 years of follow-up. There was a significant U-shaped relationship between alcohol intake and risk of hip fracture (p quadratic 0.02). Compared with long-term abstainers, the adjusted hazard ratios for hip fracture were 0.78 (95% confidence interval [CI], 0.61-1.00) among consumers of up to 14 drinks per week and 1.18 (95% CI, 0.77-1.81) among consumers of 14 or more drinks per week. Alcohol intake was associated with bone mineral density of the total hip and femoral neck in a stepwise manner, with approximately 5% (95% CI, 1%-9%) higher bone density among consumers of 14 or more drinks per week than among abstainers. These relationships were all similar among men and women.

CONCLUSIONS

Among older adults, moderate alcohol consumption has a U-shaped relationship with risk of hip fracture, but a graded positive relationship with bone mineral density at the hip.

Estrogen Receptor α Polymorphism and Risk of Cardiovascular Disease, Cancer, and Hip Fracture

BACKGROUND

We hypothesized that the estrogen receptor alpha (ESR1) IVS1-397T/C polymorphism affects high-density lipoprotein cholesterol response to hormone replacement therapy and risk of cardiovascular disease (CVD), cancer of reproductive organs, and hip fracture.

METHODS AND RESULTS

We studied cross-sectionally 9244 individuals from the Danish general population and followed them up for 23 to 25 years. End points were CVD (ischemic heart disease, myocardial infarction, angina pectoris, ischemic cerebrovascular disease, ischemic stroke, other ischemic cerebrovascular disease, venous thromboembolism, deep vein thrombosis, and pulmonary embolism), cancer of reproductive organs (breasts, ovaries, uterus, and prostate), and hip fracture. We also studied patients with ischemic heart disease (n=2495), ischemic cerebrovascular disease (n=856), and breast cancer (n=1256) versus general population controls. The CC, CT, and TT genotypes had general population frequencies of 21%, 50%, and 29%, respectively. Cross-sectionally, genotype did not influence high-density lipoprotein cholesterol response to hormone replacement therapy. In the cohort study, there were no differences in risks of CVD, cancer of reproductive organs, or hip fracture between genotypes. In case-control studies, risk of CVD did not differ between genotypes; however, the odds ratio for breast cancer in women with TT versus CC genotypes was 1.4 (95% CI, 1.1 to 1.7). Meta-analysis in men of 6 previous and the present 2 studies, including 4799 cases and 12,190 controls, showed odds ratios in CC versus CT and TT genotypes for fatal and nonfatal myocardial infarction of 0.81 (95% CI, 0.59 to 1.12) and 1.08 (95% CI, 0.97 to 1.21).

CONCLUSIONS

ESR1 IVS1-397T/C polymorphism does not influence high-density lipoprotein cholesterol response to hormone replacement therapy or risk of CVD, most cancers of reproductive organs, or hip fracture.

Polymorphisms of the VDR, ER and COLIA1 genes and osteoporotic hip fracture in elderly postmenopausal women

In view of the reported associations between osteoporosis and polymorphisms of the vitamin D receptor (VDR), collagen Ialpha1 (COLIA1) and estrogen receptor (ER) genes, an association study was performed between VDR, COLLIA1, and ER genotypes and bone mineral density, biochemical markers of bone turnover and hip fracture occurrence in Belgian older postmenopausal women. The gene polymorphisms were evaluated by restriction fragment length polymorphism analyses, using the restriction enzymes BsmI (VDR), AccB7I (COLIA1), and PvuII and XbaI (ER), respectively. As expected, bone mineral density and biochemical analyses demonstrated significant differences between hip fracture patients and elderly controls. However, no significant differences in genotype distributions or allele frequencies were observed between the cases (n = 135, age 78 +/- 9 years) and controls (n = 239, age 76 +/- 4 years) for any of the gene polymorphisms. Stratification of both study populations according to VDR, COLIA1 or ER genotype did not reveal any statistically significant difference in bone density or bone turnover between subgroups with different genotypes. In conclusion, despite its limited statistical power the outcome of this study does not support the hypothesis of a major contribution of the VDR, COLIA1 or ER polymorphisms to explain variations in bone mineral density or bone turnover, or to identify elderly women at risk of osteoporotic hip fracture.

Missense polymorphisms of the WNT16 gene are associated with bone mass, hip geometry and fractures

Two missense polymorphisms of WNT16 were associated with hip bone mineral density (BMD), the buckling ratio of the femoral neck, calcaneal ultrasound and hip fractures in individuals under 80 years of age. These results confirm the association of the WNT16 gene with bone mass and osteoporotic fractures.

INTRODUCTION

Osteoporosis has a strong genetic component. Wnt ligands stimulate the differentiation of osteoblast precursors and play a major role in skeletal homeostasis. Therefore, the aim of this study was to explore the association of allelic variants of the WNT16 gene with BMD, other structural parameters of bone and osteoporotic hip fractures.

METHODS

Six single nucleotide polymorphisms were analysed in 1,083 Caucasian individuals over 49 years of age.

RESULTS

Two missense polymorphisms (rs2908004 and rs2707466) were associated with femoral neck BMD, with average differences across genotypes of 35 mg/cm(2) (p = 0.00037 and 0.0015, respectively). Likewise, the polymorphisms were associated with calcaneal quantitative ultrasound parameters (p = 0.00004 and 0.0014, respectively) and the buckling ratio, an index of cortical instability of the femoral neck (p = 0.0007 and 0.0029, respectively). Although there were no significant differences in the genotype frequency distributions between 294 patients with hip fractures and 670 controls, among the subgroup under 80 years of age, TT genotypes were underrepresented in patients with fractures (odds ratio 0.50; CI 0.27-0.94).

CONCLUSION

Common missense polymorphisms of the WNT16 gene are associated with BMD at the hip, calcaneal ultrasound and the buckling ratio of the femoral neck, as well as with hip fractures in individuals under 80 years of age. Overall, these results confirm the association of the WNT16 locus with BMD identified in genome-wide association studies and support its role in determining the risk of osteoporotic fractures.

Wnt pathway genes in osteoporosis and osteoarthritis: differential expression and genetic association study

In comparison with hip fractures, increased expression of genes in the Wnt pathway and increased Wnt activity were found in bone samples and osteoblast cultures from patients with osteoarthritis, suggesting the involvement of this pathway in subchondral bone changes. No consistent differences were found in the genetic association study.

INTRODUCTION

This study aims to explore the allelic variations and expression of Wnt pathway genes in patients with osteoporosis and osteoarthritis.

METHODS

The expression of 86 genes was studied in bone samples and osteoblast primary cultures from patients with hip fractures and hip or knee osteoarthritis. The Wnt-related activity was assessed by measuring AXIN2 and in transfection experiments. Fifty-five SNPs of the LRP5, LRP6, FRZB, and SOST genes were analyzed in 1,128 patients.

RESULTS

Several genes were differentially expressed in bone tissue, with the lowest values usually found in hip fracture and the highest in knee osteoarthritis. Overall, seven genes were consistently upregulated both in tissue samples and in cell cultures from patients with knee osteoarthritis (BCL9, FZD5, DVL2, EP300, FRZB, LRP5, and TCF7L1). The increased expression of AXIN2 and experiments of transient transfection of osteoblasts with the TOP-Flash construct confirmed the activation of Wnt signaling. Three SNPs of the LRP5 gene and one in the LRP6 gene showed marginally significant differences in allelic frequencies across the patient groups, but they did not resist multiple-test adjustment.

CONCLUSIONS

Genes in the Wnt pathway are upregulated in the osteoarthritic bone, suggesting their involvement not only in cartilage distortion but also in subchondral bone changes.

Family history of appendicular fracture and risk of osteoporosis: a population-based study

Family and twin studies demonstrate a strong genetic component to osteoporosis, suggesting that a positive family history for this disease may be an important clinical risk factor. We have therefore explored the extent to which a history of wrist fracture in a female first-degree relative was associated with an increased risk of prevalent fracture at both appendicular and vertebral sites in a cross-sectional study design. One thousand and three Caucasian women (age range 45-64 years) were studied from a UK population cohort. Bone mineral density (BMD) was measured at the lumbar spine and femoral neck using dual-energy X-ray absorptiometry. Appendicular fractures (wrist and hip) were recorded by questionnaire and validated from radiographs and hospital records. Vertebral fractures were assessed using radiologic survey of the thoracolumbar spine and semi-automated morphometric analysis. A positive family history of osteoporotic fracture (hip and/or wrist) in either a mother and/or sister was reported in 138 of the 1003 women. When compared with those with a negative family history of fracture, BMD was significantly reduced in those with a positive history at both the spine (p = 0.02) and the hip (p = 0.02). In total, there were 63 validated fragility fractures found in the 1003 women (16 wrist, 6 hip and 41 vertebral). Family history of osteoporotic fracture was associated with an increased total risk for osteoporotic fracture, with an odds ratio (95% confidence interval) of 2.02 (1.02, 3.78). Site-specific analysis showed that a positive family history of wrist fracture was associated with a considerably elevated risk of wrist fracture, with an odds ratio of 4.24 (1.44, 12.67). These increases in risk remained after adjustment for BMD, suggesting that other genetic factors account for the familial risk of osteoporosis and fracture.

Association of a common allelic polymorphism (C677T) in the methylene tetrahydrofolate reductase gene with a reduced risk of osteoporotic fractures. A case control study in Danish postmenopausal women

Twin studies indicate a substantial genetic component in the development of osteoporosis. One of the latest studied candidate genes is the one coding for methylene tetrahydrofolate reductase (MTHFR) (C677T) in which a point mutation gives rise to a thermolabile variant of MTHFR. The aim of this study was to investigate the influence of this mutation on peripheral measures of bone density and on the odds ratios (OR) for hip and lower forearm fracture in a case control study of Danish postmenopausal women. A total of 74 women with lower forearm fracture, 41 women with hip fracture, and 207 age-matched controls were included. All had broadband ultrasound attenuation (BUA) and speed of sound (SOS) measured at the heel as well as bone mineral density (BMD) measured by dual X-ray absorptiometry at the distal forearm. The MTHFR (C677T) genotypes were determined using polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP). Only 2 of 21 individuals with the TT genotype had sustained a fracture as opposed to 46 of 142 with the CT genotype and 67 of 159 with the CC genotype (P = 0.007). Using logistic regression, the following odds ratios were found when comparing the individuals homozygotic for the C-allele with those homozygotic for the T-allele: lower forearm fracture OR = 3.93 (1.25; 12.40, P = 0.02), hip fracture OR = 6.99 (l.35; 36.92, P = 0.02) and the fractures combined OR = 4.33 (1.73; 10.81, P = 0.002). In this study, the MTHFR (C677T) genotypes were not significantly associated with BMD at the lower forearm or with ultrasound parameters measured at the calcaneus. However, a significant increase in the odds ratio of fracture was found for the wild-type C-allele.

Intake of vitamin K1 and K2 and risk of hip fractures: The Hordaland Health Study

BACKGROUND

Evidence of the effect of vitamin K on bone health is conflicting. The aim was to investigate the association between intake of vitamins K1 and K2 and subsequent risk of hip fracture in a general population sample, as well as potential effect modification by apolipoprotein E gene (APOE) status by presence of the E4 allele.

METHODS

1238 men and 1569 women 71-75 years of age were included in the community-based Hordaland Health Study 1997-1999 in Western Norway. Information on hip fracture was obtained from hospitalizations in the region from enrolment until 31 December 2009. Information on intake of vitamins K1 and K2 collected at baseline was used as potential predictors of hip fracture in Cox proportional hazards regression analyses.

RESULTS

Participants in the lowest compared to the highest quartile of vitamin K1 intake had increased risk of suffering a hip fracture (hazard ratio (HR)=1.57 [95% CI 1.09, 2.26]). Vitamin K2 intake was not associated with hip fracture. Presence of APOE4-allele did not increase the risk of hip fracture, nor was there any effect modification with vitamin K1 in relation to risk of hip fracture.

CONCLUSIONS

A low intake of vitamin K1, but not K2, was associated with an increased risk of hip fractures.

Does hip strength analysis explain the lower incidence of hip fracture in the People's Republic of China?

To explore whether there are ethnic differences in calculated hip strength that might explain the low incidence of hip fracture in China, we used Lunar DPX 'beta' version of hip strength analysis (HAS) and hip axis length (HAL) programs to compare hip geometry, calculated strength and densitometric values from Chinese subjects in Shenyang to those of Caucasian subjects in Oslo and Leuven participating in the European Prospective Osteoporosis Study (EPOS). Subjects were 210 Chinese and 403 Caucasian men and women aged 53-77 years. Parameters investigated included bone mineral density (BMD), bone mineral content (BMC), bone area (BA), cross-sectional moment of inertia (CSMI) and section modulus (both indicating strength and rigidity of the femoral neck), HAL, neck length (NL), neck diameter, tensile stress (Tstress) and compressive stress (Cstress) (indicating the stress in the femoral neck at its weakest cross section arising from walking or a standard fall, respectively), safety factor (SF, indicating the resistance to fracture for forces generated during walking) and fall index (FI, indicating the resistance to fracture from force generated during a fall in the greater trochanter). The Chinese men and women were significantly shorter and lighter than their Caucasian counterparts (P<0.01) and had significantly lower BMD, BMC and BA of the femoral neck (P<0.01). After adjusting for BA, weight and height, there was no significant ethnic difference in either gender in BMC. CSMI and section modulus were significantly lower, and HAL, NL and neck diameter were significantly shorter in the Chinese men and women (P<0.01). These differences all remained after adjusting for weight and height. There were no significant differences in Tstress, Cstress, SF and FI between ethnic groups in either gender. Most of the parameters of calculated hip strength in the Chinese subjects were similar to or poorer than those in the Caucasian subjects. There was no evidence to indicate that Shenyang Chinese have superior BMD or BMC or better calculated hip strength. The short HAL and NL of the population, however, could be an independent factor contributing to the low incidence of hip fracture.

Identification of Novel Loci Associated With Hip Shape: A Meta-Analysis of Genomewide Association Studies

We aimed to report the first genomewide association study (GWAS) meta-analysis of dual-energy X-ray absorptiometry (DXA)-derived hip shape, which is thought to be related to the risk of both hip osteoarthritis and hip fracture. Ten hip shape modes (HSMs) were derived by statistical shape modeling using SHAPE software, from hip DXA scans in the Avon Longitudinal Study of Parents and Children (ALSPAC; adult females), TwinsUK (mixed sex), Framingham Osteoporosis Study (FOS; mixed), Osteoporotic Fractures in Men study (MrOS), and Study of Osteoporotic Fractures (SOF; females) (total N = 15,934). Associations were adjusted for age, sex, and ancestry. Five genomewide significant (p < 5 × 10-9 , adjusted for 10 independent outcomes) single-nucleotide polymorphisms (SNPs) were associated with HSM1, and three SNPs with HSM2. One SNP, in high linkage disequilibrium with rs2158915 associated with HSM1, was associated with HSM5 at genomewide significance. In a look-up of previous GWASs, three of the identified SNPs were associated with hip osteoarthritis, one with hip fracture, and five with height. Seven SNPs were within 200 kb of genes involved in endochondral bone formation, namely SOX9, PTHrP, RUNX1, NKX3-2, FGFR4, DICER1, and HHIP. The SNP adjacent to DICER1 also showed osteoblast cis-regulatory activity of GSC, in which mutations have previously been reported to cause hip dysplasia. For three of the lead SNPs, SNPs in high LD (r2  > 0.5) were identified, which intersected with open chromatin sites as detected by ATAC-seq performed on embryonic mouse proximal femora. In conclusion, we identified eight SNPs independently associated with hip shape, most of which were associated with height and/or mapped close to endochondral bone formation genes, consistent with a contribution of processes involved in limb growth to hip shape and pathological sequelae. These findings raise the possibility that genetic studies of hip shape might help in understanding potential pathways involved in hip osteoarthritis and hip fracture. © 2018 The Authors. Journal of Bone and Mineral Research Published by Wiley Periodicals, Inc.

Estrogen receptor alpha genotype is associated with a reduced prevalence of radiographic hip osteoarthritis in elderly Caucasian women

PURPOSE

This study evaluated the association between polymorphisms in the estrogen receptor (ER) alpha gene (ESR1) and prevalent and incident radiographic hip osteoarthritis (RHOA) in a large, well-defined prospective cohort of elderly Caucasian women.

METHODS

Prevalent and incident RHOA was evaluated from all available pelvis X-rays obtained from the Study of Osteoporotic Fractures at baseline and after a mean of 8.3 years. Evaluable DNA samples were available from 4746 of these subjects. RHOA cases were defined by published methods. The ESR1 polymorphisms at intron I (Pvu II for a T/C substitution and Xba I for an A/G substitution) were genotyped in the context of a multiplex polymerase chain reaction (PCR) amplification followed by allele-specific single nucleotide polymorphism (SNP) detection with immobilized oligonucleotide probes in linear arrays. Multiple logistic regression was performed to estimate odds ratios (ORs) and 95% confidence intervals (95% CI) associated with the T/C and A/G polymorphisms.

RESULTS

RHOA was present in 12.1% of subjects, of whom 325 had joint space narrowing (JSN) score > or =3 and 130 had an osteophyte score > or =2 and JSN score > or =2. There was a significant reduction in the odds of prevalent RHOA for individuals with the C/C compared to T/T genotype at the Pvu II site with an OR of 0.71 (95% CI: 0.55-0.92) (P=0.01). Adjustments for age, weight, height, hip Bone mineral density (BMD) and estrogen use did not alter the relationship between the C/C genotype and reduced risk of RHOA, with an OR of 0.71 (95% CI: 0.54-0.94) (P=0.01). The risk of incident RHOA was reduced for the Pvu II C/C compared to the T/T genotype (P=0.11). Also, the reduced risk of incident RHOA in C/C subjects varied by estrogen use. There was no association between the Xba I G/G or G/A genotypes and RHOA with OR of 0.82 (95% CI: 0.61-1.10) (P=0.19) compared to women with A/A genotype.

CONCLUSIONS

We conclude that the C/C genotype of the ER alpha Pvu II polymorphism was associated with a modestly reduced risk of prevalent and incident RHOA in elderly Caucasian women. Additional work is required to understand how the intron I ESR1 polymorphism may alter joint degeneration.

Determinants of hip axis length in women aged 10-89 years: a twin study

Hip axis length (HAL), a measure of femoral geometry, has been shown to predict hip fracture in white women over the age of 67 years, independently of bone mineral density at the femoral neck. A cross-sectional study of 304 pairs of female twins [176 monozygous (MZ) and 128 dizygous (DZ)], aged between 10 and 89 years, was performed to examine the influence of age, constitutional, lifestyle, and genetic factors on HAL. HAL was calculated from dual energy X-ray absorptiometry scans of the proximal femur using an automated technique with an Hologic QDR-1000W. Lean mass, fat mass, height, and weight were also measured. Maximum mean HAL was achieved by the age of 15 years. After this age there was no discernible dependency of mean HAL on age. Using within-pair differences, after adjusting for height there were no other independent constitutional or lifestyle predictors. Cross-sectionally, after adjustment for height, MZ and DZ correlations were 0.79 (95% CI: 0.73-0.84) and 0.54 (95% CI: 0.39-0.68), respectively, and independent of age. The MZ correlation exceeded the DZ correlation (p < 0.001). The best-fitting model apportioned 79% (SE 7%) of variation in height-adjusted HAL to additive genetic factors. There was marginal evidence that an environmental influence shared by twins explained 31% (SE 16%) of height-adjusted variance (p = 0.07), in which case the genetic variance was reduced to 51% (SE 15%). Adjustment for height had reduced the magnitude of total variance by 26%, and 95% of this reduction was in the additive genetic component. Applying a previously described theoretical model, approximately 10% of the increased risk of hip fracture associated with a maternal history of hip fracture could be attributed to the genetic factors determining HAL. We conclude that, in women, adult HAL is achieved by midadolescence. After adjustment for height, which is itself largely under genetic influence, other genetic factors appear to play the predominant role in explaining variation in HAL.

Femoral neck fragility in women has its structural and biomechanical basis established by periosteal modeling during growth and endocortical remodeling during aging

To gain insight into the growth- and age-related origins of bone fragility at the proximal femur, we analyzed structural and biomechanical data of the femoral neck from a study of postmenopausal women with hip fractures and their 47 premenopausal daughters. Results were expressed as standard deviations (SD) or Z-scores (mean +/- SEM) adjusted for age and weight, derived using a normal reference population of 262 premenopausal women and 370 postmenopausal women. Women with hip fractures had increased femoral neck (FN) periosteal and endocortical diameters (1.01 +/- 0.26 SD and 1.18 +/- 0.25 SD, respectively). Cortical thickness was reduced by 0.96 +/- 0.1 SD and volumetric bone mineral density (vBMD) was reduced by 1.2 +/- 0.1 SD). The section modulus was normal while the buckling ratio was increased by 1.59 +/- 0.17 SD). Their daughters had increased FN diameter by about one half that of their mothers (0.48 +/- 0.16 SD), while endocortical diameter was increased by only one third (0.44 +/- 0.13 SD). Cortical thickness and vBMD were not reduced, the section modulus was increased (0.48 +/- 0.13 SD) while the buckling ratio was normal. We infer that the larger femoral neck size in women with hip fractures is growth-related; the wider endocortical cavity and thinner cortex is the result of excessive age-related endocortical bone resorption producing a thin cortex in a larger bone predisposing to structural failure by local buckling. The structural basis of bone fragility has some features originating during growth and others during aging.

Vitamin D receptor gene polymorphisms and the risk of fractures in older women. For the Study of Osteoporotic Fractures Research Group

The association between vitamin D receptor gene polypmorphisms and bone mineral density is controversial. The relationship between vitamin D receptor genotype and risk of fracture is uncertain. To determine whether vitamin D receptor polymorphisms were associated with the risk of hip, vertebral, and other (nonhip, nonvertebral) fractures in elderly women, we conducted a case-cohort study within a prospective study of 9704 community-dwelling women aged 65 years and older. Vitamin D receptor allele and genotype frequencies in women who experienced first incident hip (n = 181), vertebral (n = 127), and other (n = 223) fractures were compared with those of control women selected randomly from the cohort. Average length of follow-up was 6.5, 3.7, and 5.4 years for women in hip, vertebral, and other fracture analyses, respectively. Vitamin D receptor polymorphisms were determined by polymerase chain reaction amplification of genomic DNA using TaqI and ApaI restriction site endonuclease digestion. All nonvertebral fractures were confirmed by X-ray reports; hip fractures were validated by review of X-ray films. Vertebral fractures were defined by morphometry using lateral spine radiography at baseline and an average of 3.7 years later. Allele or genotype frequencies did not differ between fracture cases and their respective controls. Vitamin D receptor genotype (defined by TaqI, ApaI, or the combination of TaqI and ApaI) was not significantly associated with the risk of hip, vertebral, or other fractures. For example, compared with the referent group of women with TT genotype, those with Tt and tt genotypes had similar age- and weight-adjusted risks of fracture at the hip (hazard ratios 0.9, 95% confidence interval [CI] 0.6-1.3, and 0.8, 95% CI 0.5-1.2, respectively), spine (odds ratios 1.1, 95% CI 0.7-1.8, and 0.7, 95% CI 0.4-1.3, respectively), or other skeletal site (hazard ratios 1.0, 95% CI 0. 7-1.4, and 1.0, 95% CI 0.7-1.5, respectively). These findings were not altered in additional analyses including those adjusted for and stratified by age, ethnic ancestry, calcaneal bone density, dietary calcium intake, use of calcium supplements, use of vitamin D supplements, and oral estrogen use. We conclude that Vitamin D receptor polymorphisms defined by TaqI and ApaI are not associated with the risk of fracture in older women. Our results suggest that determination of these vitamin D receptor polymorphisms is not a clinically useful test for the prediction of fracture risk in elderly women.