Genetic and environmental correlations between bone phenotypes and anthropometric indices in Chinese

Genome-wide association study using family-based cohorts identifies the WLS and CCDC170/ESR1 loci as associated with bone mineral density

Background

Osteoporosis is a common and debilitating bone disease that is characterised by a low bone mineral density (BMD), a highly heritable trait. Genome-wide association studies (GWAS) have proven to be very successful in identifying common genetic variants associated with BMD adjusted for age, gender and weight, however a large portion of the genetic variance for this trait remains unexplained. There is evidence to suggest significant genetic correlation between body size traits and BMD. It has also recently been suggested that unintended bias can be introduced as a result of adjusting a phenotype for a correlated trait. We performed a GWAS meta-analysis in two populations (total n = 6,696) using BMD data adjusted for only age and gender, in an attempt to identify genetic variants associated with BMD including those that may have potential pleiotropic effects on BMD and body size traits.

Results

We observed a single variant, rs2566752, associated with spine BMD at the genome-wide significance level in the meta-analysis (P = 3.36 × 10⁻⁰⁹). Logistic regression analysis also revealed an association between rs2566752 and fracture rate in one of our study cohorts (P = 0.017, n = 5,654). This is an intronic variant located in the wntless Wnt ligand secretion mediator (WLS) gene (1p31.3), a known BMD locus which encodes an integral component of the Wnt ligand secretion pathway. Bioinformatics analyses of variants in moderate LD with rs2566752 produced strong evidence for a regulatory role for the variants rs72670452, rs17130567 and rs1430738. Expression quantitative trait locus (eQTL) analysis suggested that the variants rs12568456 and rs17130567 are associated with expression of the WLS gene in whole blood, cerebellum and temporal cortex brain tissue (P = 0.034–1.19 × 10⁻²³). Gene-wide association testing using the VErsatile Gene-based Association Study 2 (VEGAS2) software revealed associations between the coiled-coil domain containing 170 (CCDC170) gene, located adjacent to the oestrogen receptor 1 (ESR1) gene, and BMD at the spine, femoral neck and total hip sites (P = 1.0 × 10⁻⁰⁶, 2.0 × 10⁻⁰⁶ and 2.0 × 10⁻⁰⁶ respectively).

Conclusions

Genetic variation at the WLS and CCDC170/ESR1 loci were found to be significantly associated with BMD adjusted for only age and gender at the genome-wide level in this meta-analysis.

New models for large prospective studies: is there a risk of throwing out the baby with the bathwater?

Manolio et al. (Am J Epidemiol. 2012;175:859-866) proposed that large cohort studies adopt novel models using "temporary assessment centers" to enroll up to a million participants to answer research questions about rare diseases and "harmonize" clinical endpoints collected from administrative records. Extreme selection bias, we are told, will not harm internal validity, and "process expertise to maximize efficiency of high-throughput operations is as important as scientific rigor" (p. 861). In this article, we describe serious deficiencies in this model as applied to the United States. Key points include: 1) the need for more, not less, specification of disease endpoints; 2) the limited utility of data collected from existing administrative and clinical databases; and 3) the value of university-based centers in providing scientific expertise and achieving high recruitment and retention rates through community and healthcare provider engagement. Careful definition of sampling frames and high response rates are crucial to avoid bias and ensure inclusion of important subpopulations, especially the medically underserved. Prospective hypotheses are essential to refine study design, determine sample size, develop pertinent data collection protocols, and achieve alliances with participants and communities. It is premature to reject the strengths of large national cohort studies in favor of a new model for which evidence of efficiency is insufficient.

Sex difference between body composition and weight-bearing bone mineral density in Korean adult twins: healthy twin study

We performed a monozygotic (MZ) cotwin-control study using the MZ twin pair difference in bone mineral density (BMD) to assess the relationship between body composition and BMD at weight-bearing sites. This study controlled for common genetic factors and applied only to environmental factors, using 185 MZ twin pairs aged 30-50 years (140 male subjects, 230 female subjects). As expected, total lean mass (TLM) was greater in males and total fat mass (TFM) was greater in females. In male twins, TLM was associated with BMD at the legs, pelvis, and spine, with percent BMD increases of 0.41 (95% confidence interval [CI] 0.17-0.64), 0.62 (95% CI 0.35-0.89), and 0.27 (95% CI 0.01-0.54) for every 1 kg. In female twins, TFM was associated with BMD at the legs and pelvis, with percent BMD increases of 0.10 (95% CI 0.03-0.17) and 0.10 (95% CI 0.02-0.18) for every 1 kg. The results support the hypothesis that skeletal muscle and bone mass in middle-aged men are linked. In contrast, this association was not shown in women, and the impact of TFM on BMD was significant. Therefore, there were sex differences in the relationship of body composition on BMD.

Association of ALPL and ENPP1 gene polymorphisms with bone strength related skeletal traits in a Chuvashian population

Mineralization of the extracellular matrix of bone is an essential element of bone development, maintenance and repair. ALPL and ENPP1 genes and their products are known to be central in local regulation of bone mineralization. The present study investigates potential associations of ENPP1 and ALPL polymorphisms with several phenotypes reflecting bone size and hand BMD. The study sample included 310 Caucasian nuclear families. Forty SNPs in ALPL and 14 SNPs in ENPP1 genetic loci as well as pairwise haplotypes were tested for association with bone strength related traits. Our findings suggest that the region corresponding to exons 7 through 9 of the ALPL gene harbors functional polymorphism affecting both bone size at various skeletal sites (p-value ranged from 0.01 to 0.0001) and hand bone mineral density (p-value=0.0007). The other important finding of consistent association between bone size phenotypes and the 3' untranslated region of ENPP1 gene (p-value ranged from 0.01 to 0.001) imply functional significance of this region to bone growth. The considered anthropometric and radiographic bone phenotypes are closely related to bone fragility thus suggesting a role for both genes in osteoporosis. Further research is required to validate the relevancy of the potentially functional regions identified by our and other studies to normal and pathologic bone development as well as to determine the relevancy of the polymorphisms in ALPL and ENPP1 gene loci to clinical practice.

Evidence for major pleiotropic effects on bone size variation from a principal component analysis of 451 Caucasian families

AIM

To identify pleiotropic quantitative trait loci (QTL) influencing bone size (BS) at different skeletal sites in Caucasians.

METHODS

In a sample containing 3899 Caucasians from 451 pedigrees, 410 microsatellite markers spaced approximately 8.9 cM apart across the human genome were genotyped. Phenotypical and genetic correlations of BS at lumbar spine, hip (femoral neck, trochanter, and intertrochanter regions), and wrist (ultradistal, mid-distal, and one-third distal sites) were determined using bivariate quantitative genetic analysis. A principal component analysis (PCA) was performed to obtain principal component (PC) factors that were then subjected to variance components linkage analysis to identify regions linked to the PC.

RESULTS

Genetic correlations of BS at different skeletal sites ranged from 0.40 to 0.79 (P<0.001). The PCA yielded a PC named PCtotal, which explained up to 76% of the total (co)variation of all the BS at the 7 skeletal sites for the whole sample. We identified a QTL influencing the BS of multiple skeletal sites on chromosome 7 at 140 cM [logarithm of odds (LOD)=2.85] in the overall sample. Sex-specific evidence for linkage was observed on chromosome 11 at 53 cM (LOD =2.82) in the male-only data subset.

CONCLUSION

Our study identified several genomic regions that may have pleiotropic effects on different skeletal sites. These regions may contain genes that play a critical role in overall bone development and osteoporosis at multiple skeletal sites, hence are biologically and clinically important.

Bivariate linkage study of proximal hip geometry and body size indices: the Framingham study

Femoral geometry and body size are both characterized by substantial heritability. The purpose of this study was to discern whether hip geometry and body size (height and body mass index, BMI) share quantitative trait loci (QTL). Dual-energy X-ray absorptiometric scans of the proximal femur from 1,473 members in 323 pedigrees (ages 31-96 years) from the Framingham Osteoporosis Study were studied. We measured femoral neck length, neck-shaft angle, subperiosteal width (outer diameter), cross-sectional bone area, and section modulus, at the narrowest section of the femoral neck (NN), intertrochanteric (IT), and femoral shaft (S) regions. In variance component analyses, genetic correlations (rho ( G )) between hip geometry traits and height ranged 0.30-0.59 and between hip geometry and BMI ranged 0.11-0.47. In a genomewide linkage scan with 636 markers, we obtained nominally suggestive linkages (bivariate LOD scores > or =1.9) for geometric traits and either height or BMI at several chromosomes (4, 6, 9, 15, and 21). Two loci, on chr. 2 (80 cM, BMI/shaft section modulus) and chr. X (height/shaft outer diameter), yielded bivariate LOD scores > or =3.0; although these loci were linked in univariate analyses with a geometric trait, neither was linked with either height or BMI. In conclusion, substantial genetic correlations were found between the femoral geometric traits, height and BMI. Linkage signals from bivariate linkage analyses of bone geometric indices and body size were similar to those obtained in univariate linkage analyses of femoral geometric traits, suggesting that most of the detected QTL primarily influence geometry of the hip.

Effects of genes, sex, age, and activity on BMC, bone size, and areal and volumetric BMD

Quantitative genetic analyses of bone data for 710 inter-related individuals 8-85 yr of age found high heritability estimates for BMC, bone area, and areal and volumetric BMD that varied across bone sites. Activity levels, especially time in moderate plus vigorous activity, had notable effects on bone. In some cases, these effects were age and sex specific.

INTRODUCTION

Genetic and environmental factors play a complex role in determining BMC, bone size, and BMD. This study assessed the heritability of bone measures; characterized the effects of age, sex, and physical activity on bone; and tested for age- and sex-specific bone effects of activity.

MATERIALS AND METHODS

Measures of bone size and areal and volumetric density (aBMD and vBMD, respectively) were obtained by DXA and pQCT on 710 related individuals (466 women) 8-85 yr of age. Measures of activity included percent time in moderate + vigorous activity (%ModVig), stair flights climbed per day, and miles walked per day. Quantitative genetic analyses were conducted to model the effects of activity and covariates on bone outcomes.

RESULTS

Accounting for effects of age, sex, and activity levels, genes explained 40-62% of the residual variation in BMC and BMD and 27-75% in bone size (all p<0.001). Decline in femoral neck (FN), hip, and spine aBMD with advancing age was greater among women than men (age-by-sex interaction; all p <or= 0.05). %ModVig had the most notable effect on bone; high activity was associated with higher aBMD at all sites, but the magnitude of this effect varied. Activity among men was associated with higher FN BMC and cross-sectional area (CSA) at the 4% radius, but this was not observed among women (sex-by-activity interaction, both p <or= 0.05). Younger women had greater cortical vBMD (Cort-vBMD) than younger men, with minimal difference between low and high activity levels. Influence of activity was greater in older women: older women with low activity had lower Cort-vBMD than older men, but older women with high activity had higher Cort-vBMD than older men (age-by-sex-by-activity interaction, p=0.04).

CONCLUSIONS

High heritability estimates for DXA and pQCT measures varied across bone sites. Percent time spent in moderate to vigorous activity had the most notable effect on bone, and in some cases, this effect was age or sex specific.

Proximal hip geometry is linked to several chromosomal regions: genome-wide linkage results from the Framingham Osteoporosis Study

INTRODUCTION

Femoral geometry contributes to bone strength and predicts hip fracture risk. The purpose of this study was to evaluate heritability (h(2)) of geometric indices of the proximal hip and to perform whole-genome linkage analyses of these traits, adjusted for body size.

METHODS

DXA scans of the proximal femur from 1473 members of 323 pedigrees (age range 31-96 years) from the population-based Framingham Osteoporosis Study were obtained. Using the hip structural analysis program, we measured femoral neck length (FNL, cm) and neck-shaft angle (NSA); subperiosteal width (WID, cm), cross-sectional area (CSA, cm(2)); and section modulus (Z, cm(3)) at the narrowest section of the neck (NN), intertrochanteric (IT) and femoral shaft (S) regions. Linkage analyses were performed for the above indices with a set of 636 markers using variance components maximum likelihood method.

RESULTS

Substantial genetic influences were found for all geometric phenotypes, with h(2) values between 0.28 (NSA) and 0.70 (IT_WID). Adjustment for height and BMI did not alter h(2) of NSA and FNL but decreased h(2) of the cross-sectional indices. We obtained substantial linkage (multipoint LOD >3.0) for S_Z at 2p21 and 21q11 and S_WID at Xq25-q26. Inclusion of height and BMI as covariates resulted in much lower LOD scores for S_Z, whereas linkage signals for S_Z at 4q25, S_CSA at 4q32 and S_CSA and S_Z at 15q21 increased after the adjustment. Linkage of FNL at 1q and 13q, NSA at 2q and NN_WID at 16q did not change after the adjustment.

CONCLUSION

Suggestive linkages of bone geometric indices were found at 1q, 2p, 4q, 13q, 15q and Xq. The identification of significant linkage regions after adjustment for BMI and height may point to QTLs influencing femoral bone geometry independent of body size.

Genetic and environmental correlations between obesity phenotypes and age at menarche

OBJECTIVE

To assess the extent that the genetic and environmental factors contribute to the phenotypic correlations between obesity traits and age at menarche (AAM), and also to examine the influence of AAM on obesity in both pre- and postmenopausal women.

METHODS

F ive hundred and twelve pedigrees with 2667 Caucasian female subjects from two to four generations were recruited. Fat mass and lean mass (both in kg) were measured by dual-energy X-ray absorptiometry scanner. Body mass index (BMI) (kg/m(2)) was calculated. We performed bivariate quantitative genetic analyses in the total sample containing 2667 Caucasian women. We also selected 206 unrelated premenopausal women and 140 unrelated postmenopausal women from the total sample, and computed the respective phenotypic correlation between obesity and AAM in these two subgroups.

RESULTS

For fat mass, lean mass and BMI, we detected their significant negative genetic correlations with AAM after adjustment for significant covariates, which were -0.3170 (P<0.001), -0.1721 (P<0.05) and -0.3665 (P<0.001), respectively. However, their environmental correlations with AAM were all nonsignificant (P>0.05), ranging from -0.0016 to 0.0192. In the premenopausal subgroup, significant associations were observed between fat mass and AAM (rho=-0.231, P<0.01) as well as between BMI and AAM (rho=-0.257, P<0.01). In the postmenopausal subgroup, no such associations were observed.

CONCLUSION

Our results for the first time suggested that significant phenotypic association between obesity phenotypes and AAM is mainly attributable to shared genetic rather than environmental factors, and AAM may have stronger effects on obesity phenotypes in pre- than in postmenopausal women.

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.