Two new single-nucleotide polymorphisms in the COL1A1 upstream regulatory region and their relationship to bone mineral density

Large-scale evidence for the effect of the COLIA1 Sp1 polymorphism on osteoporosis outcomes: the GENOMOS study

BACKGROUND

Osteoporosis and fracture risk are considered to be under genetic control. Extensive work is being performed to identify the exact genetic variants that determine this risk. Previous work has suggested that a G/T polymorphism affecting an Sp1 binding site in the COLIA1 gene is a genetic marker for low bone mineral density (BMD) and osteoporotic fracture, but there have been no very-large-scale studies of COLIA1 alleles in relation to these phenotypes.

METHODS AND FINDINGS

Here we evaluated the role of COLIA1 Sp1 alleles as a predictor of BMD and fracture in a multicenter study involving 20,786 individuals from several European countries. At the femoral neck, the average (95% confidence interval [CI]) BMD values were 25 mg/cm2 (CI, 16 to 34 mg/cm2) lower in TT homozygotes than the other genotype groups (p < 0.001), and a similar difference was observed at the lumbar spine; 21 mg/cm2 (CI, 1 to 42 mg/cm2), (p = 0.039). These associations were unaltered after adjustment for potential confounding factors. There was no association with fracture overall (odds ratio [OR] = 1.01 [CI, 0.95 to 1.08]) in either unadjusted or adjusted analyses, but there was a non-significant trend for association with vertebral fracture and a nominally significant association with incident vertebral fractures in females (OR = 1.33 [CI, 1.00 to 1.77]) that was independent of BMD, and unaltered in adjusted analyses.

CONCLUSIONS

Allowing for the inevitable heterogeneity between participating teams, this study-which to our knowledge is the largest ever performed in the field of osteoporosis genetics for a single gene-demonstrates that the COLIA1 Sp1 polymorphism is associated with reduced BMD and could predispose to incident vertebral fractures in women, independent of BMD. The associations we observed were modest however, demonstrating the importance of conducting studies that are adequately powered to detect and quantify the effects of common genetic variants on complex diseases.

Assessment of linkage and association of 13 genetic loci with bone mineral density

Bone mineral density (BMD), an important risk factor for osteoporosis, is a complex trait likely affected by multiple genes. The linkage and/or association of 13 polymorphic loci of seven candidate genes (estrogen receptor alpha [ERalpha] and beta [ERbeta], calcium-sensing receptor, vitamin D receptor, collagen type 1alpha1, low-density lipoprotein [LDL] receptor-related protein 5 [LRPS], and transforming growth factor beta1) were evaluated in 177 southern Chinese pedigrees of 674 subjects, with each pedigree identified through a proband having a BMD Z score of -1.28 or less at the hip or spine. A suggestive linkage was detected between the IVS1-351A/G polymorphism of ERalpha and spine BMD, and between the 1082G/A, 1730G/A, and D14S1026 polymorphisms of ERbeta and BMD at both spine and hip. The quantitative transmission disequilibrium test (QTDT) detected total family association between 1730G/A of ERbeta and BMD at spine and hip; between D14S1026 of ERbeta and hip BMD; and between the 266A/G and 2220C/T polymorphisms of LRP5 and hip BMD. Similar total family associations were detected when only the females were analyzed. In addition, the IVS1-397T/C polymorphism of ERalpha was associated with spine BMD, and the 266A/G and 2220C/T polymorphisms of LRP5 were associated with femoral neck BMD in the females. A within-family association was detected with the IVS1-397T/C polymorphism of ERalpha, and the 266A/G and 2220C/T polymorphisms of LRP5 in the females. The effect of each polymorphism on BMD variance ranged from 1% to 4%. In conclusion, ERalpha, ERbeta and LRP5 are important candidate genes determining BMD variation, especially in females.

Genetic determinants of osteoporosis

PURPOSE OF REVIEW

Osteoporosis is a common disease with a strong genetic component characterised by reduced bone mass and an increased risk of fragility fractures. Several advances have been made over recent years in understanding the genetic basis of susceptibility to osteoporosis. This paper will review recent developments in this area.

RECENT FINDINGS

Twin studies have shown that genetic factors contribute to osteoporosis by influencing bone mineral density and other determinants of fracture risk such as ultrasound properties of bone, skeletal geometry, and bone turnover. In the normal population, many different genes contribute to the regulation of these phenotypes by interacting with environmental factors such as diet and exercise. Whereas the effect size of individual genes is small, meta-analysis has been successfully used in many cases to define the role of individual polymorphisms in predisposing to osteoporosis. Linkage studies in humans and experimental animals have identified several quantitative trait loci that regulate osteoporosis-related phenotypes, and many genes that cause monogenic bone diseases have been identified by use of this approach. It has been found that subtle polymorphisms in some of these genes also contribute to regulation of bone mass in the normal population.

SUMMARY

Research has recently begun to clarify the genes and genetic variants that predispose to osteoporosis and regulation of bone mass. Clinical applications of this research include the identification of genetic markers for assessment of fracture risk and the identification of novel molecular targets for the design of drugs that can be used to treat bone disease.

Association of interleukin 10 haplotype with low bone mineral density in Korean postmenopausal women

Osteoporosis is a disease characterized by exaggerated loss of bone mass, with as much as 50 to 85% of the variation in bone mineral density (BMD) commonly accepted as being genetically determined. Although intensive studies have attempted to elucidate the genetic effects of polymorphisms on BMD and/or osteoporosis in several genes, the genes involved are still largely unknown. The possible associations of genetic variants in five-candidate genes (IL10, CCR3, MCP1, MCP2 and GC) with spinal BMD were investigated in Korean postmenopausal women (n = 370). Fourteen SNPs in five candidate genes were genotyped, and the haplotypes of each gene constructed. The associations of adjusted spinal BMD by age, year since menopause (YSM) and body mass index (BMI), with genetic polymorphisms, were analyzed using multiple regression models. Genetic association analysis of Korean postmenopausal women revealed that IL10 -592A > C and/or IL10 ht2 were associated with decreased bone mass, whereas no significant associations were observed with all polymorphisms in other genes. The levels of spinal BMD in individuals bearing the IL10 -592CC genotype were lower (0.78 +/- 0.16) than those in others (0.85 +/- 0.17) (P = 0.02), and the BMD of IL10 ht2 bearing individuals were also lower (0.82 +/- 0.15) than those in others (0.85 +/- 0.17) (P = 0.04). Our results suggest that variants of IL10 might play a role in the decreased BMD, although additional study might need to be followed-up in a more powerful cohort.

Common variants at the PCOL2 and Sp1 binding sites of the COL1A1 gene and their interactive effect influence bone mineral density in Caucasians

BACKGROUND

Osteoporosis, mainly characterised by low bone mineral density (BMD), is a serious public health problem. The collagen type I alpha 1 (COL1A1) gene is a prominent candidate gene for osteoporosis. Here, we examined whether genetic variants at the COL1A1 gene can influence BMD variation.

METHODS

BMD was measured at nine skeletal sites in 313 Caucasian males and 308 Caucasian females. We screened four single nucleotide polymorphisms (SNPs) at the COL1A1 gene: PCOL2 (-1997 G/T) in the promoter, Sp1 (1546 G/T) in the intron 1, Gly19Cys (3911 G/A) in exon 8, and Ala897Thr (13 773 G/A) in exon 45. Univariate and multivariate association approaches were used in the analyses.

RESULTS

In multivariate analyses, we found a strong association between the PCOL2 SNP and BMD (p = 0.007 to 0.024) and a suggestive association between the Sp1 SNP and BMD (p = 0.023 to 0.048) in elderly Caucasian females. Interestingly, the interaction of these two SNPs was highly significantly associated with BMD variation (p = 0.001 to 0.003). The haplotype GG at the two SNPs had, on average, 2.7% higher BMD than non-carriers (p = 0.006 to 0.026).

CONCLUSIONS

Our data suggested that the common genetic variants at the PCOL2 and Sp1 sites, and importantly, their interactive effects, may contribute to BMD variation in elderly Caucasian females. Further studies are necessary to delineate the mechanisms underlying the effects of these common variants on BMD variation and to test their clinical relevance for general populations. In addition, our study highlighted the importance of multivariate analyses when multiple correlated phenotypes are under study.

Genetics of osteoporosis

Genetic factors play an important role in regulating bone mineral density and other phenotypes relevant to the pathogenesis of osteoporosis such as ultrasound properties of bone, skeletal geometry, and bone turnover. Progress has been made in identifying quantitative traits for regulation of bone mineral density by linkage studies in man and mouse, but relatively few causal genes have been identified. Dramatic progress has been made in identifying the genes responsible for monogenic bone diseases and it appears that polymorphisms in many of these genes also play a role in regulating bone mineral density in the general population. Advances in knowledge about the genetic basis of osteoporosis and other bone diseases offer the prospect of developing new markers for assessment of fracture risk and the identification of novel molecular targets for the design of new drug treatments for osteoporosis.

Genetic and environmental determinants of bone mineral density in Chinese women

BMD is a complex trait determined by genetic and lifestyle factors. To assess the genetic and environmental determinants of BMD in southern Chinese women, we studied a community-based cohort of 531 pre- and postmenopausal southern Chinese women and assessed the influence of 12 candidate gene loci and lifestyle risk factors on spine and hip BMD. The candidate genes studied include estrogen receptor alpha (ESR1) and beta (ESR2), calcium sensing receptor (CASR), vitamin D receptor (VDR), collagen type Ialpha1 (COLIA1), and LDL receptor-related protein 5 (LRP5). Social, medical, reproductive history, dietary habits and lifestyle factors were determined using a structured questionnaire. Single nucleotide polymorphisms (SNPs) of the COLIA1 and LRP5 gene in Chinese were determined by direct sequencing. Nucleotide (nt) -1363C/G and -1997 G/T of COLIA1, nt 266A/G, 2220C/T and 3989C/T of LRP5 gene were analyzed. Using stepwise multiple linear regression analyses, body weight was the strongest predictor for BMD in premenopausal women (n = 262), which accounted for 15.9% of the variance at the spine, 20% at femoral neck, 17.1% at trochanter, 24.3% at total hip and 10.9% at the Ward's triangle. Other significant predictors were ESR1 Ivs1-397T/C genotype (2.2% at the spine); LRP5 2220C/T genotype (1.3% at the spine, 1.6% at the trochanter); LRP5 266A/G genotype (1.1% at Ward's triangle); age at menarche (1.3% at trochanter) and age (2.0% at Ward's triangle). As for postmenopausal women (n = 269), body weight ( approximately 25% at various sites) and age (approximately 16% at femoral neck, trochanter, total hip and Ward's triangle sites) were the strongest predictors of BMD. Other significant predictors were age at menarche (4.4% at spine, 0.7% at femoral neck, 1.4% at trochanter, and 1.4% at Ward's triangle); weight bearing physical activity (2.1% at trochanter and 1% at total hip); calcium intake (1.1% at femoral neck, 0.9% at trochanter, and 1.7% at total hip) ; height (0.7% at trochanter); and ESR2 1082A/G genotype (0.8% at trochanter). We conclude that BMD at various sites and at different time span of a woman is modified by different genetic and lifestyle factors, suggesting that BMD is highly dependent on gene-environmental interactions.

The -1997 G/T polymorphism in the COLIA1 upstream regulatory region is associated with hip bone mineral density (BMD) in Chinese nuclear families

Type I collagen is the most abundant protein of bone matrix, and the collagen type I alpha 1(COLIA1) gene has been considered one of the most important candidate genes for osteoporosis. In this study, we simultaneously tested linkage and/or association of the -1997 G/T polymorphism in the COLIA1 upstream regulatory region with the variation of bone mineral density (BMD) in 1263 subjects from 402 Chinese nuclear families, consisted of both parents and at least one healthy female offspring from 20 to 45 years of age. All the subjects were genotyped by using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). BMD of the lumbar spine (L1-L4) and hip (respective and combined phenotype of the femoral neck, trochanter, and intertrochanter) was measured by dual-energy X-ray absorptiometry (DXA). By using the tests implemented in program QTDT (quantitative transmission disequilibrium test), we found significant within-family association (via TDT) between the -1997 G/T polymorphism with BMD variation at all the hip sites (respective and combined phenotypes, P < 0.05). The amount of BMD variation explained by the -1997G/T polymorphism was 1.6%, 2.0%, 1.2%, and 1.3% at the total hip, femoral neck, trochanter, and intertrochanter, respectively. Because of the limited number of sib pairs in this sample, we did not find evidence of linkage. In summary, the -1997 G/T polymorphism in the COLIA1 gene is likely to be in linkage disequilibrium with a nearby functional polymorphism affecting hip BMD, or the -1997 G/T polymorphism itself may have an important effect on the variation of hip BMD in our Chinese sample.

Tests of linkage and/or association of TGF-beta1 and COL1A1 genes with bone mass

Transforming growth factor beta 1 (TGF-beta1) is involved in bone metabolism and collagen type I alpha 1 (COL1A1) is the most abundant protein of bone matrix. Both have been considered as candidate genes for osteoporosis. In this study, we employed the transmission disequilibrium test (TDT) to examine the relationship between each of the two genes with bone mineral density (BMD) and bone mineral content (BMC) at the spine and hip in a sample of 1668 subjects from 387 Caucasian nuclear families. For the TGF-beta1 gene, three SNPs, SNP1, SNP2, and SNP4 (located in exon 1, intron 4 and intron 5, respectively) were tested and the minor allele frequencies were 30.9%, 2.1% and 27.0%, respectively. All eight possible haplotypes (TGF1-8) were observed. For the COL1A1 gene, the minor allele frequencies of SNP5, SNP6 and SNP8 (located in exon 1, intron 1, and exon 45, respectively) were 15.2%, 18.7%, 2.0%, respectively, and only six of eight potential haplotypes (COL1-6) were obtained. In the whole sample, total associations were observed between haplotype COL5 with spine BMD (P=0.027), haplotypes COL3 and TGF4 with hip BMC (P=0.002, 0.003, respectively). Within-family associations were found for spine BMD at haplotypes TGF4 (P=0.027) in female offspring families and TGF3 (P=0.021) in male offspring families. Further studies with denser markers and larger sample size are required to eventually define the relationship between these two genes with bone mass at the spine and hip.

The VDR, COL1A1, PTH, and PTHR1 gene polymorphisms are not associated with bone size and height in Chinese nuclear families

We tested the relationship of the ApaI, Eco31I, BstBI, and (AAAG)n polymorphisms in the vitamin D receptor (VDR), collagen type I alpha-1 (COL1A1), parathyroid hormone (PTH), and parathyroid hormone (PTH)/PTH-related peptide receptor (PTHR1) genes with variations in bone size (BS) and height. Population stratification, total-family association, and within-family association were used to test these relationships in 400 Chinese nuclear families with a total of 1256 individuals. The BS at hip and spine was measured using a Hologic QDR 2000 dual-energy X-ray absorptiometry (DXA) scanner. The minor allele frequencies were 29.2%, 36.0%, and 14.0% for the VDR-ApaI, COL1A1-Eco31I, and PTH-BstBI markers, respectively. (AAAG)5 and (AAAG)6 of the PTHR1 gene are two major alleles in the Chinese people. Significant population stratification was found between the spine BS and PTHR1-(AAAG)5 (P = 0.048) and PTHR1-(AAAG)6 (P = 0.023), as well as between PTHR1-(AAAG)5 and height (P = 0.048), but we did not detect any significant within-family association or total-family association between the VDR, COL1A1, PTH, and PTHR1 gene polymorphisms and the variations in BS and height in our sample. Our results do not support that the VDR, COL1A1, PTH, and PTHR1 genes have an important influence on the variation in BS and height in our Chinese population.

Genetic determinants of bone mass

PURPOSE OF REVIEW

This review examines recent advances in the analysis of genetic determinants of bone mass. It addresses both human and animal linkage studies as well as genetic manipulations in animals, inbred mouse models, and candidate gene analyses.

RECENT FINDINGS

Recent studies have implicated novel regulatory pathways in bone biology including both the neuroendocrine system and metabolic pathways linked to lipid metabolism. Variations in the lipoprotein receptor-related protein 5 (LRP5), part of the Wnt-frizzled pathway, were independently identified by linkage in high and low bone mass families. Subsequently, other high bone mass syndromes have been shown to have mutations in this gene. Neural studies have shown the skeletal regulatory activity of leptin and neuropeptide Y receptors via the hypothalamus. Subsequently, the beta-adrenergic pathway has been implicated, with important changes in bone mass. The lipoxygenase 12/15 pathway, identified through inbred mouse models and through pharmacologic studies with specific inhibitors, has also been shown to have important effects on bone mass. These studies exemplify the value of genetic models both to identify and then confirm pathways by mutational study and pharmacologic interventions. Continuing candidate gene studies often performed with multiple loci complement such discoveries. However, these studies have not focused on the clinical endpoint of fracture and few have included large enough groups to engender confidence in the associations reported, as such studies may require thousands of individuals. Interestingly, results often differ by ethnicity, age, or gender. A small proportion have examined whether relevant genes influence response to treatment.

SUMMARY

The combinations of human and animal genetic linkage studies have advanced understanding of the regulation of bone mass. Studies ranging from linkage to pharmacology provide optimism for new targets and treatments for osteoporosis.

Nmp4/CIZ regulation of matrix metalloproteinase 13 (MMP-13) response to parathyroid hormone in osteoblasts

Parathyroid hormone (PTH) regulation of matrix metalloproteinase-13 (MMP-13) expression in osteoblasts contributes to normal bone turnover. The PTH response region of the rat MMP-13 gene spans nucleotides (nt) -148 to -38 and supports binding of numerous transcription factors, including Runx2, necessary for osteoblast differentiation, c-Fos/c-Jun, and Ets-1. These trans-acting proteins mediate hormone induction via incompletely defined combinatorial interactions. Within this region, adjacent to the distal Runx2 site, is a homopolymeric(dA:dT) element (-119/-110 nt) that conforms to the consensus site for the novel transcription factor nuclear matrix protein-4/cas interacting zinc finger protein (Nmp4/CIZ). This protein regulates bone cell expression of type I collagen and suppresses BMP2-enhanced osteoblast differentiation. The aim of this study was to determine whether Nmp4/CIZ contributes to MMP-13 basal transcription and PTH responsiveness in osteoblasts. Electrophoretic mobility shift analysis confirms Nmp4/CIZ binding within the MMP-13 PTH response region. Mutation of the Nmp4/CIZ element decreases basal activity of an MMP-13 promoter-reporter construct containing the first 1329 nt of the 5'-regulatory region, and overexpression of Nmp4/CIZ protein enhances the activity of the wild-type promoter. The same mutation of the homopolymeric(dA:dT) element enhances the MMP-13 response to PTH and PGE(2). Overexpression of Nmp4/CIZ diminishes hormone induction. Mutation of both the homopolymeric(dA:dT) element and the adjacent Runx2 site further augments the PTH response. On the basis of these data and previous studies, we propose that Nmp4/CIZ is a component of a multiprotein assemblage or enhanceosome within the MMP-13 PTH response region and that, within this context, Nmp4/CIZ promotes both basal expression and hormonal synergy.

Current limitations of SNP data from the public domain for studies of complex disorders: a test for ten candidate genes for obesity and osteoporosis

BACKGROUND

Public SNP databases are frequently used to choose SNPs for candidate genes in the association and linkage studies of complex disorders. However, their utility for such studies of diseases with ethnic-dependent background has never been evaluated.

RESULTS

To estimate the accuracy and completeness of SNP public databases, we analyzed the allele frequencies of 41 SNPs in 10 candidate genes for obesity and/or osteoporosis in a large American-Caucasian sample (1,873 individuals from 405 nuclear families) by PCR-invader assay. We compared our results with those from the databases and other published studies. Of the 41 SNPs, 8 were monomorphic in our sample. Twelve were reported for the first time for Caucasians and the other 29 SNPs in our sample essentially confirmed the respective allele frequencies for Caucasians in the databases and previous studies. The comparison of our data with other ethnic groups showed significant differentiation between the three major world ethnic groups at some SNPs (Caucasians and Africans differed at 3 of the 18 shared SNPs, and Caucasians and Asians differed at 13 of the 22 shared SNPs). This genetic differentiation may have an important implication for studying the well-known ethnic differences in the prevalence of obesity and osteoporosis, and complex disorders in general.

CONCLUSION

A comparative analysis of the SNP data of the candidate genes obtained in the present study, as well as those retrieved from the public domain, suggests that the databases may currently have serious limitations for studying complex disorders with an ethnic-dependent background due to the incomplete and uneven representation of the candidate SNPs in the databases for the major ethnic groups. This conclusion attests to the imperative necessity of large-scale and accurate characterization of these SNPs in different ethnic groups.

Association between COL1A1 gene polymorphisms and bone size in Caucasians

Bone size is an important determinant of bone strength and a risk factor of osteoporotic fracture. Several studies indicate that bone size has a high heritability. Thus, a better understanding of genetic factors regulating bone size might have important clinical implications. In the present study, we examined the relationship between the collagen type I alpha 1 (COL1A1) gene and bone size at the spine, hip and wrist in a sample of 1873 subjects of Caucasian origin from 405 nuclear families. Three single-nucleotide polymorphisms (SNPs) in the COL1A1 gene were analyzed. The minor allele frequencies were 15.4, 18.8, and 1.9% for SNP1, SNP2, and SNP3, respectively. Haplotypes were reconstructed based on the family information as well as marker genotypes using the program Genehunter. We did not find evidence of population stratification, within-family association, or linkage for either single SNPs or haplotypes at any skeletal site. Suggestive evidence of total association was observed for the wrist size at SNP2 (P=0.011). After adjusting age, sex, height, and weight, subjects with the T allele of SNP2 had, on average, 3.05% smaller wrist size than noncarriers. When the subjects were divided into families with only female offspring and families with male offspring only, similar total associations were found at the wrist size for SNP2 with P-values of 0.011 and 0.010, respectively. In conclusion, the COL1A1 gene may have some effects on bone size variation at the wrist, but not at the spine or hip in our Caucasian nuclear families.

The implication of assessing a polymorphism in estrogen receptor alpha gene in the risk assessment of osteoporosis using a screening tool for osteoporosis in Asians

Both genetic and environmental factors interact to determine bone mass and the risk for developing postmenopausal osteoporosis. Recently, an Asian-specific tool, the Osteoporosis Self-Assessment Tool for Asians (OSTA), has been developed to assess the risk of osteoporosis in women. An index is calculated by multiplying the difference in body weight in kilograms and age in years by 0.2 and disregarding the decimal digits. The risk of osteoporosis is classified as high, intermediate or low according to the OSTA index less than -4, -4 to -1 and greater than -1. In the present study we examined how a single nucleotide polymorphism (SNP) in exon 8 of the estrogen receptor alpha (ERalpha) gene affected the predictive value of the OSTA index. Subjects consisted of 358 postmenopausal women who were at least 55 years old. BMDs were measured by DXA, and the SNP in the ERalpha gene was assessed by PCR-RFLP. When considering both the OSTA index and ERalpha genotype in a logistic regression model, it was found that both the OSTA index and the ERalpha genotype independently contributed to the risk of osteoporosis. The odds ratios were 1.58 (95% CI 1.26-1.91) and 2.51 (95% CI 1.42-4.44) for one unit decrement in the OSTA index and each copy of the A allele of the ERalpha genotype, respectively. The joint effect conformed more to a multiplicative model of interaction than an additive model. This suggests that persons with the high-risk genotype are at far greater risk of developing osteoporosis with advancing age or decreasing body weight, the two variables from which the OSTA index is derived. Targeting preventive measures for osteoporosis subjects with risk factors and also disease-susceptibility alleles is likely to be more cost effective.

Genetic determinants of susceptibility to osteoporosis

Osteoporosis has a strong genetic component, and clinical studies have shown that heritable factors play a key role in regulating bone mineral density, ultrasound properties of bone, skeletal geometry, and bone turnover and contribute to the pathogenesis of osteoporotic fracture. In most cases, osteoporosis is caused by the combined effects of several different genes and their interaction with environmental influences, but it can occasionally occur as the result of mutations in a single gene. Genes that have been implicated in the regulation of bone mass in humans include the genes encoding lipoprotein receptor-related protein 5, sclerostin, transforming growth factor beta-1, collagen Ialpha1, vitamin D receptor, tumor necrosis factor receptor 2, and the estrogen receptor alpha. From a clinical standpoint, advances in knowledge about the genetic basis of osteoporosis are important because they offer the prospect of developing genetic markers for the assessment of fracture risk and the opportunity to identify molecules that will be used as targets for the design of new drugs for the prevention and treatment of bone disease.