Genetic determination of variation and covariation of peak bone mass at the hip and spine

Developing and comparing deep learning and machine learning algorithms for osteoporosis risk prediction

Introduction

Osteoporosis, characterized by low bone mineral density (BMD), is an increasingly serious public health issue. So far, several traditional regression models and machine learning (ML) algorithms have been proposed for predicting osteoporosis risk. However, these models have shown relatively low accuracy in clinical implementation. Recently proposed deep learning (DL) approaches, such as deep neural network (DNN), which can discover knowledge from complex hidden interactions, offer a new opportunity to improve predictive performance. In this study, we aimed to assess whether DNN can achieve a better performance in osteoporosis risk prediction.

Methods

By utilizing hip BMD and extensive demographic and routine clinical data of 8,134 subjects with age more than 40 from the Louisiana Osteoporosis Study (LOS), we developed and constructed a novel DNN framework for predicting osteoporosis risk and compared its performance in osteoporosis risk prediction with four conventional ML models, namely random forest (RF), artificial neural network (ANN), k-nearest neighbor (KNN), and support vector machine (SVM), as well as a traditional regression model termed osteoporosis self-assessment tool (OST). Model performance was assessed by area under 'receiver operating curve' (AUC) and accuracy.

Results

By using 16 discriminative variables, we observed that the DNN approach achieved the best predictive performance (AUC = 0.848) in classifying osteoporosis (hip BMD T-score ≤ -1.0) and non-osteoporosis risk (hip BMD T-score > -1.0) subjects, compared to the other approaches. Feature importance analysis showed that the top 10 most important variables identified by the DNN model were weight, age, gender, grip strength, height, beer drinking, diastolic pressure, alcohol drinking, smoke years, and economic level. Furthermore, we performed subsampling analysis to assess the effects of varying number of sample size and variables on the predictive performance of these tested models. Notably, we observed that the DNN model performed equally well (AUC = 0.846) even by utilizing only the top 10 most important variables for osteoporosis risk prediction. Meanwhile, the DNN model can still achieve a high predictive performance (AUC = 0.826) when sample size was reduced to 50% of the original dataset.

Conclusion

In conclusion, we developed a novel DNN model which was considered to be an effective algorithm for early diagnosis and intervention of osteoporosis in the aging population.

The genetic polymorphisms of key genes in WNT pathway (LRP5 and AXIN1) was associated with osteoporosis susceptibility in Chinese Han population

BACKGROUND

Genetic factors play a critical role in the pathogenesis of osteoporosis. The imbalance of WNT/β-catenin will cause the occurrence of osteoporosis. LRP5 and AXIN1 play an important role in the classical Wnt/β-catenin signaling pathway. Our study was aimed to determine the association between five candidate single nucleotide polymorphisms (SNPs) of LRP5 or AXIN1 and osteoporosis susceptibility in Chinese Han population.

METHODS

A total of 599 osteoporosis patients and 599 healthy individuals were recruited for this case-control study. Agena MassARRAY was used to genotype SNPs. The association between SNPs and osteoporosis susceptibility in different genetic models was analyzed by PLINK software. We used false-positive report probability (FPRP) analysis to detect whether the positive results were just chance or noteworthy observations. Multifactor dimension reduction (MDR) was used to analyze the interaction of SNP-SNP in the osteoporosis risk. Finally, haplotype analysis was performed by plink1.07 and Haploview software.

RESULTS

We found that LRP5 rs11228240, AXIN1 rs2301522, and rs9921222 were significantly associated with the osteoporosis susceptibility. The results of subgroup analysis showed that LRP5 rs11228240 (protective factor) and AXIN1 rs2301522 (risk factor) were associated with the susceptibility of osteoporosis among participants who were age >60 years, female or BMI ≤ 24; AXIN1 rs9921222 significantly increased the risk of osteoporosis among participants with BMI ≤ 24. The genotype Ars2301522Crs9921222 could increase the susceptibility of osteoporosis (p = 0.026). The rs11228219LPR5, rs11228240 LPR5, rs2301522AXIN1, and rs9921222AXIN1 four-site model was the best model for predicting the osteoporosis risk (test accuracy = 0.541; CVC = 10/10).

CONCLUSIONS

The LRP5-rs11228240, AXIN1-rs2301522, and AXIN1- rs9921222 were associated with osteoporosis susceptibility in Chinese Han population.

Effective SLOPE: EffectS of Lifestyle interventions in Older PEople with obesity: a systematic review and network meta-analysis protocol

INTRODUCTION

Obesity is highly prevalent in older adults aged 65 years or older. Different lifestyle interventions (diet, exercise, self-management) are available but benefits and harms have not been fully quantified comparing all available health promotion interventions. Special consideration must be given to functional outcomes and possible adverse effects (loss of muscle and bone mass, hypoglycaemia) of weight loss interventions in this age group. The objective of this study is to synthesise the evidence regarding the effects of different types and modalities of lifestyle interventions, or their combinations, on physical function and obesity-related outcomes such as body composition in older adults with obesity.

METHODS AND ANALYSES

Six databases (Medline, Embase, Cochrane Central Register of Controlled Trials, Cumulated Index to Nursing and Allied Health Literature (CINAHL), Psychinfo and Web of Science) and two trial registries (Clinicaltrials.gov and the WHO International Clinical Trials Registry Platform) will be searched for randomised controlled trials of lifestyle interventions in older adults with obesity. Screening (title/abstract and full-text) and data extraction of references as well as assessment of risk of bias and rating of the certainty of evidence (Grading of Recommendations, Assessment, Development and Evaluation for network meta-analyses) will be performed by two reviewers independently. Frequentist random-effects network meta-analyses will be conducted to determine the pooled effects from each intervention.

ETHICS AND DISSEMINATION

We will submit our findings to peer-reviewed journals and present at national and international conferences as well as in scientific medical societies. Patient-targeted dissemination will involve local and national advocate groups.

PROSPERO REGISTRATION NUMBER

CRD42019147286.

Purinergic P2X7 receptor functional genetic polymorphisms are associated with the susceptibility to osteoporosis in Chinese postmenopausal women

Osteoporosis (OP) is a major public health problem worldwide. Genetic factors are considered to be major contributors to the pathogenesis of OP. The purinergic P2X7 receptor (P2X7R) has been shown to play a role in the regulation of osteoblast and osteoclast activity and has been considered as an important candidate gene for OP. A case-control study was performed to investigate the associations of functional single nucleotide polymorphisms (SNPs) in the P2X7R gene (rs2393799, rs7958311, rs1718119, rs2230911, and rs3751143) with susceptibility to OP in 400 Chinese OP patients and 400 controls. Results showed that rs3751143 was associated with OP; in particular, carriers of the C allele and CC/(AC + CC) genotypes were at a higher risk of OP, but no significant association of rs2230911, rs7958311, rs1718119, and rs2393799 with OP risk was observed. Analysis of the haplotypes revealed one haplotype (rs1718119G-rs2230911G-rs3751143C) that appeared to be a significant "risk" haplotype with OP. The rs3751143 polymorphism was associated with osteoclast apoptosis; ATP-induced caspase-1 activity of osteoclasts with AC and CC genotypes is lower than that of osteoclasts with AA genotype in vitro. The findings suggest that the P2X7R rs3751143 functional polymorphism might contribute to OP susceptibility in Chinese postmenopausal women.

Socioeconomic status and bone mineral density in adults by race/ethnicity and gender: the Louisiana osteoporosis study

Low bone mineral density (BMD) and osteoporosis have become a public health problem. We found that non-Hispanic white, black, and Asian adults with extremely low education and personal income are more likely to have lower BMD. This relationship is gender-specific. These findings are valuable to guide bone health interventions.

INTRODUCTION

The evidence is limited regarding the relationship between socioeconomic status (SES) and bone mineral density (BMD) for minority populations in the USA, as well as the relationship between SES and BMD for men. This study explored and examined the relationship between SES and BMD by race/ethnicity and gender.

METHODS

Data (n = 6568) from the Louisiana Osteoporosis Study (LOS) was examined, including data for non-Hispanic whites (n = 4153), non-Hispanic blacks (n = 1907), and non-Hispanic Asians (n = 508). General linear models were used to estimate the relationship of SES and BMD (total hip and lumbar spine) stratified by race/ethnicity and gender. Adjustments were made for physiological and behavioral factors.

RESULTS

After adjusting for covariates, men with education levels below high school graduate experienced relatively low hip BMD than their counterparts with college or graduate education (p < 0.05). In addition, women reporting a personal annual income under $20,000 had relatively low hip and spine BMD than their counterparts with higher income level(s) (p < 0.05).

CONCLUSIONS

Establishing a conclusive positive or negative association between BMD and SES proved to be difficult. However, individuals who are at an extreme SES disadvantage are the most vulnerable to have relatively low BMD in the study population. Efforts to promote bone health may benefit from focusing on men with low education levels and women with low individual income.

Is GSN significant for hip BMD in female Caucasians?

Low bone mineral density (BMD) is a risk factor for osteoporosis. Osteoporosis is more prevalent in females than in males. So far, the pathophysiological mechanisms underlying osteoporosis are unclear. Peripheral blood monocytes (PBMs) are precursors of bone-resorbing osteoclasts. This study aims to identify PBM-expressed proteins (genes) influencing hip BMD in humans. We utilized three independent study cohorts (N=34, 29, 40), including premenopausal Caucasians with discordant hip BMD. We studied PBM proteome-wide protein expression profiles in cohort 1 and identified 57 differentially expressed proteins (DEPs) between low vs. high BMD subjects. One protein gelsolin (GSN), after validation by Western blotting, was subject to follow-up. We compared GSN mRNA level in PBM between low vs. high BMD subjects in cohorts 2 and 3. We genotyped SNPs across GSN in 2286 unrelated Caucasians (cohort 4) and 1627 Chinese (cohort 5) and tested their association with hip BMD in females and males, respectively. We discovered and validated that GSN protein expression level in PBM was down-regulated 3.0-fold in low vs. high BMD subjects (P<0.05). Down-regulation of GSN in PBM in low BMD subjects was also observed at mRNA level in both cohort 2 and cohort 3. We identified that SNP rs767770 was significantly associated with hip BMD in female Caucasians (P=0.0003) only. Integrating analyses of the datasets at DNA, RNA, and protein levels from female Caucasians substantiated that GSN is highly significant for hip BMD (P=0.0001). We conclude that GSN is a significant gene influencing hip BMD in female Caucasians.

No association of the polymorphisms of the frizzled-related protein gene with peak bone mineral density in Chinese nuclear families

Background

The Wnt/beta-catenin signaling pathway plays an important role in skeletal development. Polymorphisms of frizzled-related protein (FRZB), an antagonist of this pathway, may generate variations in bone mineral density (BMD). In this study, we analyzed the association between FRZB genotypes and peak BMD variation in the spines and hips of two relatively large samples of Chinese female-offspring and male-offspring nuclear families.

Methods

We recruited 1,260 subjects from 401 female-offspring nuclear families and 1,296 subjects from 427 male-offspring nuclear families and genotyped four tagging single nucleotide polymorphisms (tagSNPs) (rs6433993, rs409238, rs288324, and rs4666865) spanning the entire FRZB gene. The SNPs rs288326 and rs7775, which are associated with hip osteoarthritis, were not selected in this study because of their low minor allele frequencies (MAFs) in Chinese people. The quantitative transmission disequilibrium test (QTDT) was used to analyze the association between each SNP and haplotype with peak BMD in female- and male-offspring nuclear families.

Results

In the female-offspring nuclear families, we found no evidence of an association between either single SNPs or haplotypes and peak BMD in the spine or hip. In the male-offspring nuclear families, no within-family association was observed for either SNPs or haplotypes, although a significant total association was found between rs4666865 and spine BMD (P = 0.0299).

Conclusion

Our results suggest that natural variation in FRZB is not a major contributor to the observed variability in peak BMD in either Chinese females or males. Because ethnic differences in the FRZB genotypes may exist, other studies in different population are required to confirm such results.

Comparison of whole genome linkage scans in premenopausal and postmenopausal women: no bone-loss-specific QTLs were implicated

This study was conducted to investigate if there exist bone-loss-specific quantitative trait loci (QTLs) for females. Genome-wide linkage scans were conducted in total, premenopausal, and postmenopausal women, respectively. No QTLs exclusively were found in postmenopausal women, suggesting that no bone-loss-specific QTL was implicated independent of BMD in our sample.

INTRODUCTION

Bone mineral density (BMD) in elderly women is determined jointly by peak bone mass achieved before menopause and by subsequent bone loss upon and after menopause. Peak bone mass is under strong genetic control, but whether bone loss has genetic determination independent of peak BMD is unknown.

MATERIALS AND METHODS

To investigate if there exist bone-loss-specific quantitative trait loci (QTLs) for females, we conducted genome-wide linkage scans in 2,582 Caucasian females from 451 pedigrees including 1,486 premenopausal and 1,096 postmenopausal women. Linkage analyses were performed in the total sample and premenopausal and postmenopausal women subgroups, respectively, and the results were compared.

RESULTS

No linkage evidence was found exclusively in postmenopausal women. Linkage signals identified are largely consistent in the total, premenopausal, and postmenopausal samples. For example, for spine BMD, for the total sample, a significant linkage was obtained on 15q13 (LOD = 3.67), and LOD scores of 1.52 and 2.49 were achieved on 15q13 in premenopausal and postmenopausal women, respectively.

CONCLUSIONS

We did not find any QTLs exclusively in postmenopausal women; hence, no specific QTL for bone loss was implicated independent of BMD in our female sample.

Interactions of interleukin-6 gene polymorphisms with calcium intake and physical activity on bone mass in pre-menarche Chinese girls

This study assessed independent associations and interactions of IL-6 promoter alleles (-174G/C and -634C/G), calcium intake and physical activity with bone mass among pre-menarche Chinese girls. The -634 CC carriers, greater calcium intake and physical activity were associated with better bone mass. The gene-bone association was more pronounced among girls with high physical activity or with low calcium intake.

INTRODUCTION

The association between interleukin (IL)-6 promoter polymorphisms and bone mass remains in debate. This cross-sectional study examined the association between the IL-6 promoter alleles (-174G/C and -634C/G) and bone mass, and assessed if the association could be modified by calcium intake or physical activity in pre-menarche Chinese girls.

METHODS

Two-hundred and twenty-eight healthy pre-menarche girls aged 9-11 years were recruited from primary schools in Guangzhou, China by sending letters to parents. None of them had diseases or medications known to affect bone metabolism. The IL-6 promoter genotypes were determined by PCR-RFLP, and BMD and BMC at the total body, lumbar spine, total hip and femoral neck were measured by DXA. Calcium intake and physical activity were assessed by face-to-face questionnaire interview.

RESULTS

One hundred and seventy-six subjects completed the entire study. We did not detect gene polymorphism at the IL-6 -174G/C locus, all were GG homozygotes. The IL-6 -634C/G polymorphism was significantly associated with both BMD and BMC even after adjusting for age and weight. Girls with CC genotype had higher levels of BMC and BMD than G allele carriers (+8.3% for the total body BMC, and +2.9%, +5.8%, and +5.7% for BMDs at the total body, total hip, and femoral neck, respectively; P < 0.05). The favorable effect of physical activity on BMDs at the total hip and femoral neck was much more pronounced in CC carriers than in G allele carriers, and the CC genotype associated higher BMDs at the total hip and femoral neck were observed only in girls with high level physical activity (P for interactions = 0.036 and 0.021, adjusted for age and weight). Calcium had a more benefit to the total body BMC in G allele carriers than in CC carriers, and the G allele-associated lower total body BMC was found only in subjects with low calcium intake.

CONCLUSION

The IL-6 -634C/G polymorphism was significantly associated with BMD and the association might be modified by calcium intake or physical activity in pre-menarche Chinese girls.

Impact of genetics on low bone mass in adults

Low bone mass in adults is a major risk factor for low-impact fractures and is considered of complex origin because of interaction of environmental and genetic factors, each with modest effect. The objective was to assess the relative impact of genetics and environment and quantify the risk in relatives of osteopenic individuals. We studied 440 Icelandic nuclear families with 869 first-degree relatives of both sexes. Index cases (male or female) had BMD in the lumbar spine or hip >1.5 SD less than sex-matched controls. Heritability of BMD was estimated by maximum likelihood method, and variance component analysis was used to partition the genetic and environmental effects. Relative risk of low BMD (< -1 SD) in first-degree relatives was estimated, and heritable decrement in BMD was calculated compared with controls. Heritability was estimated as 0.61-0.66. Relative risk among first-degree relatives was 2.28, and the yield of screening was as high as 36%. The genetic influence was consistent with one or a few genes with considerable effect in addition to multiple genes each with a small effect. The genetic deficit in BMD was already present before 35 yr of age and equaled bone loss during 8-30 yr after menopause. We confirmed that genetics are more important than environment to low bone mass in adults. Our results are consistent with a few underlying genes with considerable effect. The prevalence among first-degree relatives of both sexes is common, suggesting that screening them should be cost effective and informative to elucidate the underlying genetics.

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

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

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

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

INTRODUCTION

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

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

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

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

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

Disruption of four-and-a-half LIM 2 decreases bone mineral content and bone mineral density in femur and tibia bones of female mice

Four-and-a-half LIM 2 (FHL2) is a member of a family of LIM domain proteins which mediate protein-protein interactions. FHL2 acts as a coactivator and binds to important regulators of bone formation such as insulin-like growth factor binding protein (IGFBP)-5, androgen receptor, and beta-catenin. We hypothesized that FHL2 is an important regulator of bone formation. We evaluated growth and skeletal parameters in FHL2 knockout (KO) and wild-type (WT) mice at 4, 8, and 12 weeks of age. At 4 weeks of age, lack of FHL2 reduced femur, tibia, and total bone mineral content (BMC) and body weight in all mice. A gender-by-treatment interaction (P <or= 0.05) was observed for several parameters due to a greater reduction in females. Specifically, femur BMC was reduced 11-27% at 8 and 12 weeks of age and BMD was reduced 7-13% at all ages in female KO mice (P < 0.05). A similar reduction was observed in the tibias at 8 weeks of age. A 6% reduction (P = 0.07) in femur cortical thickness was observed at 12 weeks of age in female KO mice. Interestingly, a gender-specific reduction in IGFBP-5 expression was observed in the femurs of female KO mice. During differentiation of bone marrow stromal cells into osteoblasts, expression of osteocalcin, alkaline phosphatase, and bone sialoprotein was reduced 47-96% in FHL2 KO cells (P < 0.001). In conclusion, FHL2 is an important regulator of peak bone mass, lack of FHL2 produces gender- and site-specific effects on bone accretion and IGFBP-5 expression, and FHL2 is important for optimal osteoblast differentiation in vitro.

Exclusion mapping of chromosomes 1, 4, 6 and 14 with bone mineral density in 79 Caucasian pedigrees

Low bone mineral density (BMD) is a major determinant of osteoporosis and is under strong genetic control. A large number of linkage and association studies for BMD variation have been conducted, with the results being largely inconsistent. Linkage exclusion analysis is a useful tool for gene mapping but has never been used on BMD. In the present study, we conducted a linkage exclusion mapping for BMD variation on chromosomes 1, 4, 6 and 17 in 79 Caucasian pedigrees. For hip BMD variation, several genomic regions were excluded for effect sizes of 10% or greater, including regions of 61-77 cM at 1p35-p34, 167-196 cM at 1q21-q23 and 261-291 cM at 1q42-q44; 85-112 cM at 4q21-q25 and 146-150 cM at 4q31; and 77-85 cM at 6p12-q13. For spine BMD, we were able to exclude the regions of 168-189 cM at 1q21-q23, 92-94 cM at 4q21 and 106-107 cM at 4q24 and 56-103 cM at 17q12-q25, as having effect sizes of 10% or greater. These results suggest that a number of candidate genes located in the excluded regions, such as interleukin 6 receptor (IL6R) gene, type I collagen alpha 1 (COL1A1) gene and bone morphogenetic protein-3 (BMP3) gene are unlikely to have a substantial effect on BMD variation in this Caucasian population. Along with previous studies searching for genes underlying BMD variation, the current study has further delineated the genetic basis of BMD variation and provided valuable information for future genetic studies.

CA repeat polymorphism of the TNFR2 gene is not associated with bone mineral density in two independent Caucasian populations

Osteoporosis has a strong genetic component, but the genes involved are poorly defined. Genome-wide scans in multiple populations have identified chromosome 1p36 as one region linked to bone mineral density (BMD). The tumor necrosis factor receptor 2 (TNFR2) at 1p36 is a positional and functional candidate gene in osteoporosis. In this study, we conducted linkage and association tests between the CA repeat polymorphism of the TNFR2 gene and BMD in two large independent samples using the quantitative transmission disequilibrium test (QTDT) program. The first group of subjects was composed of 1836 individuals from 79 multigeneration pedigrees. The second group was a randomly ascertained set of 636 individuals from 157 nuclear families. We found no evidence of association or linkage for spine or hip BMD in the samples of the multigenerational pedigrees or nuclear families. Through testing for association and for linkage, our data do not support the TNFR2 gene as a QTL underlying hip or spine BMD variation in our Caucasian populations.

Genetic determination and correlation of body mass index and bone mineral density at the spine and hip in Chinese Han ethnicity

The purpose of the present study was to evaluate the magnitude of genetic determination of spine and hip bone mineral density (BMD) and body mass index (BMI), and to explore the genetic, environmental, and phenotypic correlations among the above phenotypes in Chinese Han ethnicity. The sample was composed of at least 217 complete nuclear families in Chinese Han ethnicity. BMD at the spine and hip was measured using a dual-energy X-ray absorptiometry scanner. The heritability (h2) of BMI and BMD at the spine and hip, the genetic correlation (rhoG) and environmental correlation (rhoE) among the three phenotypes were evaluated via variance analysis, with age, sex, and age-by-sex interaction as covariates. The phenotypic correlation (rhoP) and the bivariate heritability rhoG2 were also calculated. The heritability for BMD and BMI was approximately 0.70 and approximately 0.50, respectively (p<0.0001). The common environment shared by household members (household effect) is significant for BMI variation (p=0.0004). Significant genetic, environmental, and phenotypic correlation was observed. The rhoG2 values were 0.13 for BMI/spine BMD, 0.18 for BMI/hip BMD, and 0.58 for the spine BMD/hip BMD. While BMD at the spine and hip have significant genetic determination, BMI is more likely to be affected by environmental factors than BMD. In addition, BMD at the spine and hip shares more genetic effect (pleiotropy) than BMI and BMD do in Chinese Han ethnicity, though the effects are significant for both.

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.

The (CA)n polymorphism of the TNFR2 gene is associated with peak bone density in Chinese nuclear families

Low peak bone density (PBD) in adulthood is an important determinant of osteoporotic fracture (OF) in the elderly. The tumor necrosis factor receptor 2 (TNFR2) gene has been considered as an important candidate gene for PBD due to its important role in bone turnover. In this study, we recruited a total of 1,263 subjects from 402 Chinese nuclear families composed of both parents and at least one daughter, and tested the association of the (CA)(n) polymorphism in intron 4 of the TNFR2 gene with PBD using a more contemporary quantitative transmission disequilibrium test (QTDT). Significant within-family association was detected between the CA16 allele and bone mineral density (BMD) at the lumbar spine with the P-value of 0.005 after permutations, which is still significant after correction for multiple testing. Some evidence of total-family association between the CA16 allele and lumbar spine BMD was found (P=0.021), although the significant level did not reach the empirical threshold (P< or =0.007). About 3.14% of lumbar spine BMD variation can be explained by the CA16 allele. In summary, our results suggest that the TNFR2 gene may play an important role in determining lumbar spine BMD variation in Chinese women.

No major effect of the insulin-like growth factor I gene on bone mineral density in premenopausal Chinese women

Osteoporosis is a major public health problem, mainly characterized by low bone mineral density (BMD). BMD is a complex trait that is determined by multiple genes. Insulin-like growth factor I (IGF-I) is an important growth factor of bone and thus IGF-I gene has been considered as an attractive candidate gene for osteoporosis. A few studies on the relationship between variants of the IGF-I gene and BMD variation, via traditional association and/or linkage methods, have yielded conflicting results. In this study, we simultaneously tested association and/or linkage of a cytosine-adenine (CA) repeat polymorphism at 1 kb upstream of the transcription initiation site of the IGF-I gene with BMD variation in a large cohort of premenopausal Chinese women. A total of 1263 subjects from 402 Chinese nuclear families were examined. Each family consists of both parents and at least one daughter aged between 20 and 45 years. BMDs (g/cm(2)) at the lumbar spine and hip were measured using dual-energy X-ray absorptiometry (DXA). Applying the QTDT (quantitative transmission disequilibrium tests) progam, we did not find significant evidence of association or linkage between the CA repeat polymorphism of the IGF-I gene and BMD variation at any skeletal site. Our data do not support the IGF-I gene having major effect on BMD variation in premenopausal Chinese women.

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.

Risk of wrist fracture in women is heritable and is influenced by genes that are largely independent of those influencing BMD

Using a classical twin design study, we estimated the genetic contribution to liability of wrist fracture in women to be statistically and clinically significant. BMD is highly heritable, but statistical models showed very little overlap of shared genes between the two traits.

INTRODUCTION

Studies have observed contradictory evidence for genetic effects influencing the outcome of osteoporotic fracture, in part because of the methodological problems involved in analyzing age-related "censored" outcomes. Although a shared genetic etiology is often assumed between fracture and low BMD, this has not been shown to be the case.

MATERIALS AND METHODS

In a study of 6570 white healthy female volunteer twins between 18 and 80 years of age, we identified and validated 220 nontraumatic wrist fracture cases. From this we estimated the population prevalence, case-wise twin concordance, heritability in liability to wrist fracture (WF), and the genetic contribution to WFs controlling for age by analyzing the survival outcome using generalized linear mixed models implemented in Winbugs software. We included forearm BMD as a co-variate in some of the models to test whether there is a shared genetic etiology between WFs and BMD.

RESULTS

The prevalence of WFs in women was estimated to be 3.3% with a case-wise concordance in monozygotic twins of 0.28 and 0.11 in dizygotic twins. The additive polygenic heritability in liability was approximately 54%, and a significant genetic etiology was confirmed by analyzing WFs as a survival outcome. The magnitude of the genetic influence on risk of WFs reduced very little when BMD was included as a co-variate in the survival analysis model.

CONCLUSIONS

There is an important genetic contribution to the risk of WFs, but for the most part, these genes are unlikely to play a direct etiological role in the development of low BMD. If these results are confirmed for other sites, fracture and low BMD will have their own specific genetic risk factors that are unlikely to be shared between the two traits. This has important clinical and research implications.

Association and linkage analyses of interleukin-6 gene 634C/G polymorphism and bone phenotypes in Chinese

In this study, we tested the interleukin-6 (IL-6) gene as an important candidate gene for its linkage and association with the variation of bone phenotypes (bone mineral density [BMD] and bone size) in young Chinese female subjects. We genotyped the IL-6 gene at the -634C/G restriction fragment length polymorphism (RFLP) site (ID, RS1800796) in 1263 individuals from 402 Chinese nuclear families, composed of both parents and at least one healthy daughter (mean age +/- SD, 31.4 +/- 5.8 years). Using the daughters' bone phenotypes, we tested total-family association, within-family association (via transmission disequilibrium test, [TDT]), and linkage, between the -634C/G marker and bone phenotypes at the spine and the hip. No significant association or linkage was found for bone size and BMD, although a trend was observed for linkage between the IL-6 gene -634C/G marker and L1-4 spinal BMD (adjusted for age, weight, and height). Our results, together with the findings from other studies, indicate that the IL-6 gene, although important for postmenopausal bone loss, may have a limited impact on peak bone mass variation in a Chinese population.

Heritability of spinal trabecular volumetric bone mineral density measured by QCT in the Diabetes Heart Study

The heritability of trabecular volumetric bone mineral density (BMD) determined by quantitative computed tomography (QCT) has not yet been reported. The purpose of this study was to investigate the heritability of BMD as determined by QCT and DXA in 124 women and 120 men (age 39-83 years, BMI 17-75, 84% type 2 diabetics) from 101 families (232 sibling pairs) in the Diabetes Heart Study. Volumetric BMD had a heritability (h2) estimate of 0.73 (SE = 0.15, P < 0.0001) at the lumbar spine and 0.71 (SE = 0.15, P < 0.0001) at the thoracic spine. Areal BMD heritability estimates were 0.56 for PA spine, 0.43 for total hip, 0.43 for femoral neck, 0.45 for distal radius, 0.42 for mid-radius, and 0.52 for whole body (all P < 0.01). After accounting for familial correlation using generalized estimating equations, volumetric BMD was inversely associated with age (r = -0.52, P < 0.0001) and duration of diabetes (r = -0.24, P < 0.01) and positively associated with body weight (r = 0.25, P < 0.01). In multivariate analysis, adjustment for age, sex, and race lowered the h2 estimates for volumetric BMD at the lumbar (h2 = 0.41, P < 0.01) and thoracic (h2 = 0.48, P < 0.001) spine, increased the h2 estimate for areal BMD at the mid radius (h2 = 0.58, P < 0.0001), and had little effect on the h2 estimate for areal BMD at other sites (h2 = 0.41-0.55, all P < 0.01). Additional adjustment for BMI, duration of diabetes, and physical activity had little effect on the h2 estimates for volumetric BMD or areal BMD except at the hip where they were lowered (h2 = 0.31-0.33, all P < 0.05). These data suggest that, like areal BMD, volumetric BMD is highly heritable and may be used in designing linkage studies to locate genes governing bone metabolism.

A second-stage genome scan for QTLs influencing BMD variation

Low bone mineral density (BMD) is a major risk factor for osteoporotic fracture. To identify genomic regions harboring quantitative trait loci (QTLs) contributing to BMD variation, we performed a two-stage genome screen. The first stage involved genotyping of a sample of 53 pedigrees with 630 individuals using 400 microsatellite markers spaced at approximately 10-cM intervals throughout the genome. Ten genomic regions with multi- and/or two-point LOD scores greater than 1.5 were observed. In the present second-stage study, 60 microsatellite markers, with a mean spacing of about 5 cM, were genotyped in these regions in an expanded sample of 79 pedigrees that contained 1816 subjects. Each pedigree was ascertained through a proband with extreme BMD at the hip or spine. BMD at the spine (L1-4), hip (the femoral neck, trochanter, and intertrochanteric region), and wrist (the ultradistal region) was measured by dual-energy X-ray absorptiometry (DXA) and was adjusted for age, sex, height, and weight. Two-point and multipoint linkage analyses were performed for each BMD site using statistical genetic methods that are implemented in the computer package SOLAR. Several regions (7q11, 10q26, 12q13, and 12q24) achieved LOD scores in excess of 1 in the second-stage followup study. The current results replicate some of our previous linkage findings and also highlight some of the difficulties facing microsatellite linkage mapping for complex human diseases.

Test of linkage and/or association between the estrogen receptor alpha gene with bone mineral density in Caucasian nuclear families

Extensive studies have been performed on the association between the estrogen receptor alpha (ER-alpha) gene and bone mineral density (BMD). Despite considerable efforts, the studies using limited markers and relatively small sample size have yielded largely inconsistent results. In this study, 1873 Caucasian subjects from 405 nuclear families containing 1512 sib pairs were recruited. BMD at the lumbar spine (LS) and femoral neck (FN) was measured by dual-energy X-ray absorptiometry (DXA). Seven single-nucleotide polymorphisms (SNPs) spanning from exon 1 to 8 in the ER-alpha gene were genotyped. The program QTDT (quantitative transmission disequilibrium test) was applied to test linkage and/or association of the ER-alpha gene and BMD variation using individual SNP markers and reconstructed haplotypes. Linkage disequilibrium (LD) was generally detected for SNPs in the ER-a gene (P < 0.05). Associations were observed between SNP rs932477 and FN BMD (P = 0.028), and between the most predominant three-marker haplotype (GCG) containing SNP rs932477 and FN BMD (P = 0.010). Within-family association (present only with both linkage and association) between SNP rs2228480 (G2014A) and FN BMD (P = 0.015) was observed. The most predominant seven-SNP haplotype (TCGCGGG) was associated with higher LS BMD (P = 0.015). However, after correction for multiple testing, these associations did not reach statistical significance. Denser markers may be necessary to better define the relationship between the ER-alpha gene and BMD variation in our sample.

Genetic determinants of osteoporosis susceptibility in a female Ashkenazi Jewish population

PURPOSE

To determine the heritability of low bone mineral density (BMD) at the hip in Ashkenazi Jewish families.

METHODS

BMD at hip was accessed by dual x-ray absorptiometry (DEXA) in 166 female subjects from 61 families. Variance component analysis was used to estimate genetic contributions.

RESULTS

We observed significant genetic contributions to age-adjusted BMD at the femoral neck as measured by heritability 0.67 (P < 0.0001).

CONCLUSION

There is significant genetic determination in decreased BMD at the femoral neck in an Ashkenazi Jewish female population. These results warrant further gene mapping studies in this population to identify osteoporosis susceptibility loci.

Complex segregation analyses of bone mineral density in Chinese

China has the largest population in the world; approximately 7% of the total population suffers from primary osteoporosis. Osteoporosis is mainly characterized by low bone mineral density (BMD). In the present study, familial correlation and segregation analyses for spine and hip BMDs have been undertaken for the first time in a Chinese sample composed of 401 nuclear families with a total of 1260 individuals. The results indicate a major gene of additive inheritance for hip BMD, whereas there is no evidence of a major gene influencing spine BMD. Significant familial residual effects are found for both traits, and heritability estimates (+/-SE) for spine and hip BMDs are 0.807(0.099) and 0.897(0.101), respectively. Sex and age differences in genotype-specific average BMD are also observed. This study provides the first evidence quantifying the high degree of genetic determination of BMD variation in the Chinese.

High heritability of bone size at the hip and spine in Chinese

Bone size, an independent determinant of bone strength, is an important risk factor for osteoporotic fracture. In the present study, we investigated the magnitude of the genetic determination of bone size at the spine and hip and their genetic covariation (if any) in a population of Chinese residing in Shanghai City of P.R. China. The subjects were 50 healthy full-sib pairs of females, 188 mother-daughter pairs, and 128 husband-wife pairs selected from 401 nuclear families. Bone size (centimeters squared) was measured at the spine and hip by dual-energy X-ray absorptiometry (DEXA). The narrow-sense heritabilities h2 (SE) of bone size at the spine and hip were 0.63 (0.14) and 0.45 (0.14) respectively when estimated by full-sib pairs, and 0.60 (0.07) and 0.69 (0.07) respectively when estimated by mother-daughter pairs. Marginally significant genetic correlation was observed between the spine and hip bone size. The significantly and moderately high h2 values for bone size demonstrated in this study warrant a subsequent genetic study to search for the genes or genomic regions underlying the phenotype in Chinese.

Linkage and association of the CA repeat polymorphism of the IL6 gene, obesity-related phenotypes, and bone mineral density (BMD) in two independent Caucasian populations

Genetic factors play an important role in osteoporosis and obesity, two serious public health problems in the world. We investigated the relationships between obesity-related phenotypes, bone mineral density (BMD) and the CA repeat polymorphism of the IL6 gene in two large independent samples using the quantitative transmission disequilibrium test (QTDT). The first sample consisted of 1,816 individuals from 79 multigenerational pedigrees. Each pedigree was identified through a proband with BMD Z-scores </=-1.28 at the hip or spine. The second sample was a randomly ascertained set of 636 individuals from 157 nuclear families. Ten alleles containing 9-18 CA repeats were identified in our Caucasian populations. For body mass index (BMI), fat mass and percentage fat mass (PFM), highly significant (P<0.01) or significant (P<0.05) results were found for linkage in our sample of nuclear families and for association in the multigenerational pedigrees. We also observed weak evidence for linkage (P=0.069) with spine BMD and for association with hip BMD in the sample of multigenerational pedigrees. Our results suggest that genetic variation in or near the IL6 locus may be involved in the etiology of obesity and osteoporosis.

Estrogen receptor alpha gene polymorphisms and peak bone density in Chinese nuclear families

PBD is an important determinant of osteoporotic fractures. Few studies were performed to search for genes underlying PBD variation in Chinese populations. We tested linkage and/or association of the estrogen receptor alpha gene polymorphism with PBD in 401 Chinese nuclear families. This study suggests the ER-alpha gene may have some minor effects on PBM variation in the Chinese population. Low peak bone density (PBD) in adulthood is an important determinant of osteoporotic fractures in the elderly. PBD variation is mainly regulated by genetic factors. Extensive molecular genetics studies have been performed to search for genes underlying PBD variation, largely in whites. Few studies were performed in Chinese populations. In this study, we simultaneously test linkage and/or association of the estrogen receptor alpha (ER-alpha) gene polymorphism with PBD in 401 Chinese nuclear families (both parents plus their female children) of 1260 subjects, with the 458 children generally between 20 and 40 years of age. All the subjects were genotyped by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) at polymorphic PvuII and XbaI sites inside the ER-alpha gene. Bone mineral density was measured at the lumbar spine (L1-L4) and hip (femoral neck, trochanter, and intertrochanteric region). Raw bone mineral density values were adjusted by age, height, and weight as covariates. We detected marginally significant results for within-family association (transmission disequilibrium; p = 0.054) between the spine bone mineral density variation and the ER-alpha XbaI genotypes. For the hip bone mineral density variation, significant (p < 0.05) linkage results were generally found for the two intragenic markers. Analyses of the haplotypes defined by the two markers confer further evidence for linkage of the ER-alpha with the hip PBD variation. In conclusion, this study suggests that the ER-alpha gene may have minor effects on PBD variation in our Chinese population.

Several genomic regions potentially containing QTLs for bone size variation were identified in a whole-genome linkage scan

Bone size is an important determinant of osteoporotic fractures. For a sample of 53 pedigrees that contains more than 10,000 relative pairs informative for linkage analyses, we performed a whole-genome linkage scan using 380 microsatellite markers to identify genomic regions that may contain QTLs of bone size (two dimensional measurement by dual energy X-ray absorptiometry). We conducted two- and multi-point linkage analyses. Several potentially important genomic regions were identified. For example, the genomic region 17q23 may contain a QTL for wrist (ultra distal) bone size variation; a LOD score of 3.98 is achieved at D17S787 in two-point analyses and a maximum LOD score (MLS) of 3.01 is achieved in multi-point analyses in 17q23. 19p13 may contain a QTL for hip bone size variation; a LOD score of 1.99 is achieved at D19S226 in two-point analyses and a MLS of 2.83 is achieved in 19p13 in multi-point analyses. The genomic region identified on chromosome 17 for wrist bone size seems to be consistent with that identified for femur head width variation in an earlier whole-genome scan study. The genomic regions identified in this study and an earlier investigation on one-dimensional bone size measurement by radiography are compared. The two studies may form a basis for further exploration with larger samples and/or denser markers for confirmation and fine mapping studies to eventually identify major functional genes and the associated etiology for osteoporosis.

Differentiation of Caucasians and Chinese at bone mass candidate genes: implication for ethnic difference of bone mass

Bone mineral density (BMD) is an important risk factor for osteoporosis and has strong genetic determination. While average BMD differs among major ethnic groups, several important candidate genes have been shown to underlie BMD variation within populations of the same ethnicity. To investigate whether important candidate genes may contribute to ethnic differences in BMD, we studied the degree of genetic differentiation among several important candidate genes between two major ethnic groups: Caucasians and Chinese. The genetic variability of these two populations (1131 randomly selected individuals) was studied at six restriction sites exhibiting polymorphisms of five important candidate genes for BMD: the BsaHI polymorphism of the calcium-sensing receptor (CASR) gene, the SacI polymorphism of the alpha2HS-glycoprotein (AHSG) gene, the PvuII and XbaI polymorphisms of the estrogen receptor alpha (ESR1) gene, the ApaI polymorphism of the vitamin D receptor (VDR) gene, and the BstBI polymorphism of the parathyroid hormone (PTH) gene. The two ethnic groups showed significant allelic and genotypic differentiation of all the polymorphisms studied. The mean FST was 0.103, which significantly differed from zero (P < 0.01). The Chinese population had lower mean heterozygosity (0.331) than the Caucasian one (0.444); the CASR-BsaHI and PTH-BstBI polymorphisms contributed most significantly to this difference. Analysis of the intra- and inter-population variability suggests that various types of natural selection may affect the observed patterns of variation at some loci. If some of the candidate genes we studied indeed underlie variation in BMD, their population differentiation revealed here between ethnic groups may contribute to understanding ethnic difference in BMD.

A whole-genome linkage scan suggests several genomic regions potentially containing quantitative trait Loci for osteoporosis

Osteoporosis is an important health problem, particularly in the elderly women. Bone mineral density (BMD) is a major determinant of osteoporosis. For a sample of 53 pedigrees that contain 1249 sibling pairs, 1098 grandparent-grandchildren pairs, and 2589 first cousin pairs, we performed a whole- genome linkage scan using 380 microsatellite markers to identify genomic regions that may contain quantitative trait loci (QTL) of BMD. Each pedigree was ascertained through a proband with BMD values belonging to the bottom 10% of the population. We conducted two-point and multipoint linkage analyses. Several potentially important genomic regions were suggested. For example, the genomic region near the marker D10S1651 may contain a QTL for hip BMD variation (with two-point analysis LOD score of 1.97 and multipoint analysis LOD score of 2.29). The genomic regions near the markers D4S413 and D12S1723 may contain QTLs for spine BMD variation (with two-point analysis LOD score of 2.12 and 2.17 and multipoint analysis LOD score of 3.08 and 2.96, respectively). The genomic regions identified in this and some earlier reports are compared for exploration in extension studies with larger samples and/or denser markers for confirmation and fine mapping to eventually identify major functional genes involved in osteoporosis.

Tests of linkage and/or association of genes for vitamin D receptor, osteocalcin, and parathyroid hormone with bone mineral density

Bone mineral density (BMD) is a major determinant of osteoporotic fractures (OFs). The heritability of BMD ranges from 50% to 90% in human populations. Extensive molecular genetic analyses have been performed through traditional linkage or association approaches to test and identify genes or genomic regions underlying BMD variation. The results, particularly those concerning the vitamin D receptor (VDR) gene, have been inconsistent and controversial. In this study, we simultaneously test linkage and/or association of the genes for VDR, osteocalcin (also known as bone Gla protein [BGP]), and parathyroid hormone (PTH) with BMD in 630 subjects from 53 human pedigrees. Each of these pedigrees was ascertained through a proband with an extreme BMD value at the hip or spine (Z score < or = -1.28). For the raw BMD values, adjusting for significant covariate effects of age, sex, and weight, we performed tests for linkage alone, association alone, and then both linkage and association. For the spine BMD, at the two markers (ApaI and FokI) inside the VDR gene we found evidence for linkage (p < 0.05) and for both linkage and association by the transmission disequilibrium test (TDT; p < 0.05); association was detected (p < 0.07) with regular statistical testing by analyses of variance (ANOVA). In addition, significant results were found for association alone (p < 0.05), linkage alone (p = 0.0005), and for linkage and association (p = 0.0019) for the intragenic marker HindIII of the BGP gene for the hip BMD. Through testing for association, linkage, and linkage and association simultaneously, our data support the VDR gene as a quantitative trait locus (QTL) underlying spine BMD variation and the BGP gene as a QTL underlying hip BMD variation. However, our data do not support the PTH gene as a QTL underlying hip or spine BMD variation. This is the first study in the broad field of bone genetics that tests candidate genes as QTLs for BMD by testing simultaneously for association alone, for linkage alone, and for association and linkage (via the TDT).

Role of genetics in osteoporosis

Osteoporosis is a disease characterized by fragile bones and high susceptibility to low-trauma fractures. It is a serious health problem, especially in elderly women. Bone mineral density (BMD) has been employed most commonly as the index for defining and studying osteoporosis. BMD has high genetic determination, with heritability ranging from 50 to 90%. Various gene-mapping approaches have been applied to identify specific genes underlying osteoporosis, largely using BMD as the study phenotype. We review here the genetic determination of osteoporosis as defined by BMD and discuss a fundamental issue we encounter in genetic research in osteoporosis: the choice of phenotype(s) to study. We briefly summarize and discuss advantages and disadvantages of various approaches used in genetic studies of osteoporosis. Finally, we review and discuss the current status for mapping and identification of genes for osteoporosis. We focus on linkage studies in humans and quantitative trait loci mapping in mice to supplement the already extensive reviews of association studies made by many investigators for candidate genes.

Relevance of the genes for bone mass variation to susceptibility to osteoporotic fractures and its implications to gene search for complex human diseases

We investigate the relevance of the genetic determination of bone mineral density (BMD) variation to that of differential risk to osteoporotic fractures (OF). The high heritability (h(2)) of BMD and the significant phenotypic correlations between high BMD and low risk to OF are well known. Little is reported on h(2) for OF. Extensive molecular genetic studies aimed at uncovering genes for differential risks to OF have focussed on BMD as a surrogate phenotype. However, the relevance of the genetic determination of BMD to that of OF is unknown. This relevance can be characterized by genetic correlation between BMD and OF. For 50 Caucasian pedigrees, we estimated that h(2) at the hip is 0.65 (P < 0.0001) for BMD and 0.53 (P < 0.05) for OF; however, the genetic correlation between BMD and OF is nonsignificant (P > 0.45) and less than 1% of additive genetic variance is shared between them. Hence, most genes found important for BMD may not be relevant to OF at the hip. The phenotypic correlation between high BMD and low risk to OF at the hip (approximately -0.30) is largely due to an environmental correlation (rho(E) = -0.73, P < 0.0001). The search for genes for OF should start with a significant h(2) for OF and should include risk factors (besides BMD) that are genetically correlated with OF. All genes found important for various risk factors must be tested for their relevance to OF. Ideally, employing OF per se as a direct phenotype for gene hunting and testing can ensure the importance and direct relevance of the genes found for the risk of OF. This study may have significant implications for the common practice of gene search for complex diseases through underlying risk factors (usually quantitative traits).

Determination of bone size of hip, spine, and wrist in human pedigrees by genetic and lifestyle factors

Osteoporosis is a major public health problem defined as a loss of bone strength, of which bone size is an important determinant. Compared with extensive studies on bone mass, studies on the importance of factors determining variation in bone size are relatively few. In particular, the significance of genetic factors is largely unknown. In 49 pedigrees with 703 subjects bone sizes of the hip, spine, and wrist were measured by dual X-ray absorptiometry. We evaluated the contribution of genetic factors in determining variation in bone size of the hip, spine, and wrist while studying age, sex, weight, height, exercise, smoking, alcohol consumption, and the interaction among these factors as covariates for their effects on bone size. We found that, on average, males have larger bone sizes. Male bone sizes at the spine and hip increased with age; however, the effect of age in our female subjects was nonsignificant. Height invariably affected bone size at all the sites studied. Alcohol consumption and exercise generally had significant effects in increasing bone size at the spine and/or hip in both males and females. After adjusting for sex, age, weight, height, lifestyle factors, and the significant interactions among these factors, heritabilities (+/-SE) were, respectively, 0.48 (0.09), 0.64 (0.08), and 0.60 (0.09) for bone size at the hip, spine, and wrist.

Reconsidering the effects of antiresorptive therapies in reducing osteoporotic fracture

Concepts of what constitutes osteoporosis have evolved from the single criterion of low bone mass to a more inclusive consideration of bone strength, based on both quantity and quality. The evidence driving this shift is drawn from many sources. For example, recent studies of bone geometry have shown what engineers have always known: material properties and structural strength are inseparable. Genetic factors also argue against a one-dimensional (ID) view of osteoporosis. Large-scale family studies present a strong case for genetic influences on bone mass and predisposition to fracture. The contribution of aging to fracture risk has long been known, but we are only now beginning to understand what happens to bone remodeling and microstructure in an aging skeleton. The recognition that osteoporosis is far more complex than previously thought suggests that factors in addition to bone mineral density (BMD) may be useful for evaluating bone fragility and therapeutic effectiveness. Although assessment of BMD is noninvasive and widely available, the degree of increase in BMD alone fails to account for the broader effectiveness of antiresorptive agents in reducing the risk of fractures related to osteoporosis. Indeed, the very multiplicity of factors that determine fracture risk implies that response to therapy may be equally complex. Studies of response to antiresorptive agents and the cellular processes they induce are at best preliminary at this time. Although new technologies have been applied to studying bone microarchitecture, their invasive nature limits wide use. New methods are needed to provide insight into the causes and effects of bone fragility. The definition of osteoporosis, meanwhile, must still be considered a work in progress.

Characterization of genetic and lifestyle factors for determining variation in body mass index, fat mass, percentage of fat mass, and lean mass

In this study, we simultaneously characterized genetic and lifestyle factors (exercise, smoking, and alcohol consumption) in determining variation in body mass index (BMI), fat mass, percentage of fat mass (PFM), and lean mass while adjusting for the effects of age and sex. Six hundred fifty-eight Caucasian individuals from 48 pedigrees were studied for BMI. Among these individuals, 289 from 38 pedigrees were studied for fat mass, PFM, and lean mass measured by dual X-ray absorptiometry (DXA). After adjusting for age, sex, and lifestyle factors, the heritabilities (h(2)) of BMI, fat mass, PFM, and lean mass ranged from 0.52 to 0.57 with associated standard errors ranging from 0.09 to 0.14. After accounting for significant sex and age effects, exercise had significant effects for all the phenotypes studied, and the effects of smoking and alcohol consumption were not significant. Therefore, significant proportions of variation in BMI, fat mass, PFM, and lean mass were under genetic control, and exercise had a significant effect in reducing BMI, fat mass, and PFM and in increasing lean mass. This study warrants further genetic linkage analyses to search for genes for the obesity-related phenotypes measured by DXA in our population.

Body composition predicts bone mineral density and balance in premenopausal women

Low bone mineral density (BMD) and poor stability both contribute to increased risk of fractures associated with a fall. Our aim in this cross-sectional study was to determine the anthropometric and/or performance variables that best predicted BMD and stability in women. BMD, body composition, muscle strength, muscle power, and dynamic stability were evaluated in 61 women (age 40 +/- 4 years; % body fat 27% +/- 5%). In correlation analyses, BMD at all sites was significantly related to height, lean mass, strength, and leg power (r2 = 0.25-0.49). Significant inverse relationships were found between all independent variables and dynamic stability (r2 = 0.23-0.52). In stepwise regression, lean mass independently predicted BMD at the femoral neck (R2 = 0.20), total hip (R2 = 0.24), and whole body (R2 = 0.17), whereas hip abductor torque predicted 23% of the variance in trochanter BMD and added 6% to the variance in total hip BMD. Leg power was the only predictor of spine BMD (R2 = 0.14). Fat and lean mass both independently predicted poor performance on postural stability, with fat mass contributing 31% of the total variance (R2 = 0.38). In conclusion, we found lean mass to be a robust predictor of BMD in premenopausal women. Furthermore, both hip abductor torque and leg power independently predicted BMD at clinically relevant fracture sites (hip and spine). The finding that higher fat mass contributes to the majority of the variance in poor stability indicates that greater fat mass may compromise stability and, thus, increase fall risk in heavier individuals.

Determination of bone mineral density of the hip and spine in human pedigrees by genetic and life-style factors

In 40 human pedigrees with 563 subjects, we evaluated the contribution of genetic and life-style factors (exercise, smoking, and alcohol consumption) and the interactions between non-genetic factors in determining bone mineral density (BMD) of the hip and spine. In our analysis, we adjusted for age, weight, height, menopausal status in females, life-style factors, and the significant interactions among these factors. For the spine and hip BMD, heritabilities (h(2)) (+/- SE) were, respectively, 0.68 (0.21) and 0.86 (0.28) in males and 0.64 (0.13) and 0.67 (0.14) in females. Exercise had significant beneficial effects for male spine BMD and female hip BMD. Alcohol consumption experienced in our sample had significant beneficial effects on hip BMD in both sexes. Although the main effect of smoking was not significant, there were significant interaction effects between smoking and other important factors (e.g., exercise, weight, alcohol consumption). For example, for female spine BMD, exercise had significant beneficial effects in smokers; however, its effect in non-smokers was non-significant. This result indicates that exercise may reduce deleterious effects of smoking (if any) on BMD, but may have minor effects in increasing BMD in non-smokers. The various interaction effects among risk factors explicitly revealed here for the first time indicate that the detailed effects and direction of individual risk factors may depend on the presence and magnitude of other factors. Weight invariably affected BMD of the hip and spine in both sexes. Age effects were significant for hip BMD, but not for male spine BMD.