Genome scan for QTLs underlying bone size variation at 10 refined skeletal sites: genetic heterogeneity and the significance of phenotype refinement

Genetics of Skeletal Evolution in Unusually Large Mice from Gough Island

Organisms on islands often undergo rapid morphological evolution, providing a platform for understanding mechanisms of phenotypic change. Many examples of evolution on islands involve the vertebrate skeleton. Although the genetic basis of skeletal variation has been studied in laboratory strains, especially in the house mouse Mus musculus domesticus, the genetic determinants of skeletal evolution in natural populations remain poorly understood. We used house mice living on the remote Gough Island-the largest wild house mice on record-to understand the genetics of rapid skeletal evolution in nature. Compared to a mainland reference strain from the same subspecies (WSB/EiJ), the skeleton of Gough Island mice is considerably larger, with notable expansions of the pelvis and limbs. The Gough Island mouse skeleton also displays changes in shape, including elongations of the skull and the proximal vs. distal elements in the limbs. Quantitative trait locus (QTL) mapping in a large F₂ intercross between Gough Island mice and WSB/EiJ reveals hundreds of QTL that control skeletal dimensions measured at 5, 10, and/or 16 weeks of age. QTL exhibit modest, mostly additive effects, and Gough Island alleles are associated with larger skeletal size at most QTL. The QTL with the largest effects are found on a few chromosomes and affect suites of skeletal traits. Many of these loci also colocalize with QTL for body weight. The high degree of QTL colocalization is consistent with an important contribution of pleiotropy to skeletal evolution. Our results provide a rare portrait of the genetic basis of skeletal evolution in an island population and position the Gough Island mouse as a model system for understanding mechanisms of rapid evolution in nature.

Genetic perturbations that impair functional trait interactions lead to reduced bone strength and increased fragility in mice

Functional adaptation may complicate the choice of phenotype used in genetic studies that seek to identify genes contributing to fracture susceptibility. Often, genetic variants affecting one trait are compensated by coordinated changes in other traits. Bone fracture is a prototypic example because mechanical function of long bones (stiffness and strength) depends on how the system coordinately adjusts the amount (cortical area) and quality (tissue-mineral density, TMD) of bone tissue to mechanically offset the natural variation in bone robustness (total area/length). We propose that efforts aimed at identifying genes regulating fracture resistance will benefit from better understanding how functional adaptation contributes to the genotype-phenotype relationship. We analyzed the femurs of C57BL/6J-Chr(A/J)/NaJ Chromosome Substitution Strains (CSSs) to systemically interrogate the mouse genome for chromosomes harboring genes that regulate mechanical function. These CSSs (CSS-i, i=the substituted chromosome) showed changes in mechanical function on the order of -26.6 to +11.5% relative to the B6 reference strain after adjusting for body size. Seven substitutions showed altered robustness, cortical area, or TMD, but no effect on mechanical function (CSS-4, 5, 8, 9, 17, 18, 19); six substitutions showed altered robustness, cortical area, or TMD, and reduced mechanical function (CSS-1, 2, 6, 10, 12, 15); and one substitution also showed reduced mechanical function but exhibited no significant changes in the three physical traits analyzed in this study (CSS-3). A key feature that distinguished CSSs that maintained function from those with reduced function was whether the system adjusted cortical area and TMD to the levels needed to compensate for the natural variation in bone robustness. These results provide a novel biomechanical mechanism linking genotype with phenotype, indicating that genes control function not only by regulating individual traits, but also by regulating how the system coordinately adjusts multiple traits to establish function.

Association analyses of vitamin D-binding protein gene with compression strength index variation in Caucasian nuclear families

This study was conducted to test whether there exists an association between vitamin D-binding protein (DBP) gene and compression strength index (CSI) phenotype. Candidate gene association analyses were conducted in total sample, male subgroup, and female subgroup, respectively. Two single-nucleotide polymorphisms (SNPs) with significant association results were found in males, suggesting the importance of DBP gene polymorphisms on the variation in CSI especially in Caucasian males.

INTRODUCTION

CSI of the femoral neck (FN) is a newly developed phenotype integrating information about bone size, body size, and bone mineral density. It is considered to have the potential to improve the performance of risk assessment for hip fractures because it is based on a combination of phenotypic traits influencing hip fractures rather than a single trait. CSI is under moderate genetic determination (with a heritability of approximately 44% found in this study), but the relevant genetic study is still rather scarce.

METHODS

Based on the known physiological role of DBP in bone biology and the relatively high heritability of CSI, we tested 12 SNPs of the DBP gene for association with CSI variation in 405 Caucasian nuclear families comprising 1,873 subjects from the Midwestern US. Association analyses were performed in the total sample, male and female subgroups, respectively.

RESULTS

Significant associations with CSI were found with two SNPs (rs222029, P = 0.0019; rs222020, P = 0.0042) for the male subgroup. Haplotype-based association tests corroborated the single-SNP results.

CONCLUSIONS

Our findings suggest that the DBP gene might be one of the genetic factors influencing CSI phenotype in Caucasians, especially in males.

Differentially expressed genes strongly correlated with femur strength in rats

The region of chromosome 1q33-q54 harbors quantitative trait loci (QTL) for femur strength in COPxDA and F344xLEW F2 rats. The purpose of this study is to identify the genes within this QTL region that contribute to the variation in femur strength. Microarray analysis was performed using RNA extracted from femurs of COP, DA, F344 and LEW rats. Genes differentially expressed in the 1q33-q54 region among these rat strains were then ranked based on the strength of correlation with femur strength in F2 animals derived from these rats. A total of 214 genes in this QTL region were differentially expressed among all rat strains, and 81 genes were found to be strongly correlated (r(2)>0.50) with femur strength. Of these, 12 candidate genes were prioritized for further validation, and 8 of these genes (Ifit3, Ppp2r5b, Irf7, Mpeg1, Bloc1s2, Pycard, Sec23ip, and Hps6) were confirmed by quantitative PCR (qPCR). Ingenuity Pathway Analysis suggested that these genes were involved in interferon alpha, nuclear factor-kappa B (NFkB), extracellular signal-related kinase (ERK), hepatocyte nuclear factor 4 alpha (HNF4A) and tumor necrosis factor (TNF) pathways.

A bivariate whole genome linkage study identified genomic regions influencing both BMD and bone structure

Areal BMD (aBMD) and areal bone size (ABS) are biologically correlated traits and are each important determinants of bone strength and risk of fractures. Studies showed that aBMD and ABS are genetically correlated, indicating that they may share some common genetic factors, which, however, are largely unknown. To study the genetic factors influencing both aBMD and ABS, bivariate whole genome linkage analyses were conducted for aBMD-ABS at the femoral neck (FN), lumbar spine (LS), and ultradistal (UD)-forearm in a large sample of 451 white pedigrees made up of 4498 individuals. We detected significant linkage on chromosome Xq27 (LOD = 4.89) for LS aBMD-ABS. In addition, we detected suggestive linkages at 20q11 (LOD = 3.65) and Xp11 (LOD = 2.96) for FN aBMD-ABS; at 12p11 (LOD = 3.39) and 17q21 (LOD = 2.94) for LS aBMD-ABS; and at 5q23 (LOD = 3.54), 7p15 (LOD = 3.45), Xq27 (LOD = 2.93), and 12p11 (LOD = 2.92) for UD-forearm aBMD-ABS. Subsequent discrimination analyses indicated that quantitative trait loci (QTLs) at 12p11 and 17q21 may have pleiotropic effects on aBMD and ABS. This study identified several genomic regions that may contain QTLs important for both aBMD and ABS. Further endeavors are necessary to follow these regions to eventually pinpoint the genetic variants affecting bone strength and risk of fractures.

Genomic expression analysis of rat chromosome 4 for skeletal traits at femoral neck

Hip fracture is the most devastating osteoporotic fracture type with significant morbidity and mortality. Several studies in humans and animal models identified chromosomal regions linked to hip size and bone mass. Previously, we identified that the region of 4q21-q41 on rat chromosome (Chr) 4 harbors multiple femoral neck quantitative trait loci (QTLs) in inbred Fischer 344 (F344) and Lewis (LEW) rats. The purpose of this study is to identify the candidate genes for femoral neck structure and density by correlating gene expression in the proximal femur with the femoral neck phenotypes linked to the QTLs on Chr 4. RNA was extracted from proximal femora of 4-wk-old rats from F344 and LEW strains, and two other strains, Copenhagen 2331 and Dark Agouti, were used as a negative control. Microarray analysis was performed using Affymetrix Rat Genome 230 2.0 arrays. A total of 99 genes in the 4q21-q41 region were differentially expressed (P < 0.05) among all strains of rats with a false discovery rate <10%. These 99 genes were then ranked based on the strength of correlation between femoral neck phenotypes measured in F2 animals, homozygous for a particular strain's allele at the Chr 4 QTL and the expression level of the gene in that strain. A total of 18 candidate genes were strongly correlated (r(2) > 0.50) with femoral neck width and prioritized for further analysis. Quantitative PCR analysis confirmed 14 of 18 of the candidate genes. Ingenuity pathway analysis revealed several direct or indirect relationships among the candidate genes related to angiogenesis (VEGF), bone growth (FGF2), bone formation (IGF2 and IGF2BP3), and resorption (TNF). This study provides a shortened list of genetic determinants of skeletal traits at the hip and may lead to novel approaches for prevention and treatment of hip fracture.

Pleiotropic patterns of quantitative trait loci for 70 murine skeletal traits

Quantitative trait locus (QTL) studies of a skeletal trait or a few related skeletal components are becoming commonplace, but as yet there has been no investigation of pleiotropic patterns throughout the skeleton. We present a comprehensive survey of pleiotropic patterns affecting mouse skeletal morphology in an intercross of LG/J and SM/J inbred strains (N = 1040), using QTL analysis on 70 skeletal traits. We identify 798 single-trait QTL, coalescing to 105 loci that affect on average 7-8 traits each. The number of traits affected per locus ranges from only 1 trait to 30 traits. Individual traits average 11 QTL each, ranging from 4 to 20. Skeletal traits are affected by many, small-effect loci. Significant additive genotypic values average 0.23 standard deviation (SD) units. Fifty percent of loci show codominance with heterozygotes having intermediate phenotypic values. When dominance does occur, the LG/J allele tends to be dominant to the SM/J allele (30% vs. 8%). Over- and underdominance are relatively rare (12%). Approximately one-fifth of QTL are sex specific, including many for pelvic traits. Evaluating the pleiotropic relationships of skeletal traits is important in understanding the role of genetic variation in the growth and development of the skeleton.

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.

Sex-specific genetic loci for femoral neck bone mass and strength identified in inbred COP and DA rats

INTRODUCTION

Hip fracture is the most devastating osteoporotic fracture type with significant morbidity and mortality. Several studies in humans identified chromosomal regions linked to hip size and bone mass. Animal models, particularly the inbred rat, serve as complementary approaches for studying the genetic influence on hip fragility. The purpose of this study is to identify sex-independent and sex-specific quantitative trait loci (QTLs) for femoral neck density, structure, and strength in inbred Copenhagen 2331 (COP) and Dark Agouti (DA) rats.

MATERIALS AND METHODS

A total of 828 (405 males and 423 females) F(2) progeny derived from the inbred COP and DA strains of rats were phenotyped for femoral neck volumetric BMD (vBMD), cross-sectional area, polar moment of inertia (Ip), neck width, ultimate force, and energy to break. A whole genome screen was performed using 93 microsatellite markers with an average intermarker distance of 20 cM. Recombination-based marker maps were generated using MAPMAKER/EXP from the COP x DA F(2) data and compared with published Rat Genome Database (RGD) maps. These maps were used for genome-wide linkage analyses to detect sex-independent and sex-specific QTLs.

RESULTS

Significant evidence of linkage (p < 0.01) for sex-independent QTLs were detected for (1) femoral neck vBMD on chromosomes (Chrs) 1, 6, 10, and 12, (2) femoral neck structure on Chrs 5, 7, 10, and 18, and (3) biomechanical properties on Chrs 1 and 4. Male-specific QTLs were discovered on Chrs 2, 9, and 18 for total vBMD, on Chr 17 for trabecular vBMD, on Chr 9 for total bone area, and on Chr 15 for ultimate force. A female-specific QTL was discovered on Chr 2 for ultimate force. The effect size of the individual QTL varied between 1% and 4%.

CONCLUSIONS

We detected evidence that sex-independent and sex-specific QTLs contribute to hip fragility in the inbred rat. Several QTLs regions identified in this study are homologous to human chromosomal regions previously linked to QTLs contributing to femoral neck and related phenotypes.

A whole genome linkage scan for QTLs underlying peak bone mineral density

We conducted a whole genome linkage scan for quantitative trait loci (QTLs) underlying peak bone mineral density (PBMD). Our efforts identified several potential genomic regions for PBMD and highlighted the importance of epistatic interaction and sex-specific analyses in identifying genetic regions underlying PBMD variation.

INTRODUCTION

Peak bone mineral density (PBMD) is an important clinical risk predictor of osteoporosis and explains a large part of bone mineral density (BMD) variation.

METHODS

To detect susceptive quantitative trait loci (QTLs) for PBMD variation including consideration of epistatic and sex-specific effects, we conducted a whole genome linkage scan (WGLS) for PBMD using 2,200 Caucasians from 207 pedigrees, aged 20-50 years. All the individuals were genotyped with 410 microsatellite markers. In addition to WGLS in the total combined sample of males and females, we conducted epistatic interaction analyses, and sex-specific subgroup linkage analyses.

RESULTS

We identified several potential genomic regions that met the criteria for suggestive linkage. The most impressing region is 12p12 for hip PBMD (LOD = 2.79) in the total sample. Epistatic interaction analyses found a significant epistatic interaction between 12p12 and 22q13 (p = 0.0021) for hip PBMD. Additionally, we detected suggestive linkage evidence at 15q26 (LOD = 2.93), 2p13 (LOD = 2.64), and Xq27 (LOD = 2.64). Sex-specific analyses suggested the presence of sex-specific QTLs for PBMD variation.

CONCLUSIONS

Our efforts identified several potential regions for PBMD and highlighted the importance of epistatic interaction and sex-specific analyses in identifying genetic regions underlying PBMD variation.

Genomic regions identified for BMD in a large sample including epistatic interactions and gender-specific effects

A genome-wide linkage scan was conducted using a large white sample to identify QTLs for BMD. We found QTLs in the total sample and the gender-specific subgroups, as well as significant epistatic interactions underlying BMD variations.

INTRODUCTION

Low BMD is an important risk factor for osteoporosis and under strong genetic control.

MATERIALS AND METHODS

To identify quantitative trait loci (QTLs) for regulation of BMD, we performed a large-scale whole genome linkage scan (WGS) involving 4126 individuals from 451 families. In addition to the conventional linkage analyses in the total combined sample of males and females, we conducted epistatic interaction analyses and gender-specific linkage analyses.

RESULTS

Significant linkage was detected on 5q23 for wrist BMD (LOD = 3.39) and 15q13 for female spine BMD (LOD = 4.49). For spine BMD, we revealed significant epistatic interactions between 3p25 and 2q32 (p = 0.0022) and between 3p25 and 11q23 (p = 0.0007). We replicated several genomic regions that showed linkage with BMD in previous studies by others and ours, such as 3p21, 1p36, and Xq27.

CONCLUSIONS

This study highlights the importance of large sample size, incorporation of epistatic interaction, and consideration of gender-specific effects in identifying QTLs for BMD variation. The results of this study provide a foundation for the future fine mapping and gene identification in our population.

Molecular genetic studies of gene identification for osteoporosis: a 2004 update

This review summarizes comprehensively the most important and representative molecular genetics studies of gene identification for osteoporosis published up to the end of December 2004. It is intended to constitute a sequential update of our previously published review covering the available data up to the end of 2002. Evidence from candidate gene association studies and genome-wide linkage studies in humans, as well as quantitative trait locus mapping animal models are reviewed separately. Studies of transgenic and knockout mice models relevant to osteoporosis are summarized. An important extension of this update is incorporation of functional genomic studies (including DNA microarrays and proteomics) on osteogenesis and osteoporosis, in light of the rapid advances and the promising prospects of the field. Comments are made on the most notable findings and representative studies for their potential influence and implications on our present understanding of genetics of osteoporosis. The format adopted by this review should be ideal for accommodating future new advances and studies.

Identification of a quantitative trait locus on rat chromosome 4 that is strongly linked to femoral neck structure and strength

Risk factors for osteoporotic hip fracture include reduced bone mineral density and poor structure of the femoral neck, both of which are heritable traits. Previously, we showed that despite similar body size, Fischer 344 (F344) rats have significantly different skeletal traits compared with Lewis (LEW) rats. To identify a gene or genes regulating fracture risk at the femoral neck, we mapped quantitative trait loci (QTL) for femoral neck density and structure phenotypes using a 595 F2 progeny derived from the inbred F344 and LEW strains of rats. Femoral neck phenotypes included volumetric bone mineral density (vBMD), neck width, femoral neck cross-sectional area and polar moment of inertia (Ip). A 20-cM genome-wide scan was performed using 118 microsatellite markers and linkage analysis was conducted to identify chromosomal regions harbor QTL for femoral neck phenotypes. Strong evidence of linkage (P<0.01) to femoral neck vBMD was observed on chromosomes (Chrs) 1, 2, 4, 5, 7, 10 and 15. QTL affecting femoral neck structure and biomechanical properties were detected only on Chr 4 where the F344 alleles were shown to improve femoral neck structure, whereas these alleles had no effect on bone measurements at the lumbar spine and only modest effects at the femoral midshaft. In contrast, QTL on Chrs 1, 2 and 10 affected multiple skeletal sites. Several QTL regions in this study are homologous to human chromosomal regions, where linkage to femoral neck and related phenotypes has been reported previously. These findings represent an important first step in localizing and identifying genes that influence hip fragility.

Genome-wide scan identified QTLs underlying femoral neck cross-sectional geometry that are novel studied risk factors of osteoporosis

A genome-wide screen was conducted using a large white sample to identify QTLs for FNCS geometry. We found significant linkage of FNCS parameters to 20q12 and Xq25, plus significant epistatic interactions and sex-specific QTLs influencing FNCS geometry variation.

INTRODUCTION

Bone geometry, a highly heritable trait, is a critical component of bone strength that significantly determines osteoporotic fracture risk. Specifically, femoral neck cross-sectional (FNCS) geometry is significantly associated with hip fracture risk as well as genetic factors. However, genetic research in this respect is still in its infancy.

MATERIALS AND METHODS

To identify the underlying genomic regions influencing FNCS variables, we performed a remarkably large-scale whole genome linkage scan involving 3998 individuals from 434 pedigrees for four FNCS geometry parameters, namely buckling ratio (BR), cross-sectional area (CSA), cortical thickness (CT), and section modulus (Z). The major statistical approach adopted is the variance component method implemented in SOLAR.

RESULTS

Significant linkage evidence (threshold LOD = 3.72 after correction for tests of multiple phenotypes) was found in the regions of 20q12 and Xq25 for CT (LOD = 4.28 and 3.90, respectively). We also identified eight suggestive linkage signals (threshold LOD = 2.31 after correction for multiple tests) for the respective geometry traits. The above findings were supported by principal component linkage analysis. Of them, 20q12 was of particular interest because it was linked to multiple FNCS geometry traits and significantly interacted with five other genomic loci to influence CSA variation. The effects of 20q12 on FNCS geometry were present in both male and female subgroups. Subgroup analysis also revealed the presence of sex-specific quantitative trait loci (QTLs) for FNCS traits in the regions such as 2p14, 3q26, 7q21 and 15q21.

CONCLUSIONS

Our findings laid a foundation for further replication and fine-mapping studies as well as for positional and functional candidate gene studies, aiming at eventually finding the causal genetic variants and hidden mechanisms concerning FNCS geometry variation and the associated hip fractures.

Variation in femoral length is associated with polymorphisms in RUNX2 gene

INTRODUCTION

Bone size is an important determinant of bone strength. Although it is well established that bone size traits are under the strong genetic control, genes involved in their determination are poorly characterized. The major objective of the present study was to test hypothesis of possible association between three RUNX2 SNP polymorphisms (rs2819858, rs1406846, rs2819854) and anthropometrical femoral length (FEML). In addition, the possibility of association between anthropometrical tibial length (TIBL) and stature and chosen RUNX2 polymorphisms was tested.

MATERIALS AND METHODS

The study was conducted on 265 nuclear families comprised of a total of 904 individuals. DNA samples were available for 705 individuals, belonging to 212 nuclear families. Three different transmission disequilibrium tests (TDTs), population-based and pedigree-based (PDT) association analyses were implemented in order to test the working hypothesis.

RESULTS

The results unambiguously and consistently demonstrated significant association for FEML regardless of the specific polymorphism tested and type of analysis implemented. The P values obtained by TDTs ranged between 0.0155 and 0.0007. The effect of RUNX2 polymorphisms was estimated to explain 1.9% of the total FEML variation after adjustment for sex and age. The data suggested that the strength of association between RUNX2 polymorphisms and FEML may be higher in females (P = 0.007) than in males (P = 0.046), according to PDT. Conversely, no reliable evidence of association between RUNX2 polymorphisms and either TIBL or stature was found.

CONCLUSIONS

For the first time, the evidence of association between RUNX2 polymorphisms and FEML was provided. The results of the present research contribute to the deeper understanding of the genetic architecture of femoral size and introduce the issues of site and sex dependency of the extent of RUNX2 effect. Further studies are required to confirm our findings, specifically focused on clinically oriented sites of skeleton, like femoral neck.

Linkage exclusion mapping with bone size in 79 Caucasian pedigrees

Bone size is an important risk factor of osteoporotic fractures and has strong genetic determination. However, genetic studies on bone size variation are relatively rare. In the present study, we conducted a linkage exclusion mapping for bone size variation on chromosomes 1, 4, 6, and 17 in 79 Caucasian pedigrees. For hip bone size variation, several genomic regions were excluded at effect sizes of 10% or greater, including regions of 61-77cM at 1p35-p34, 43-59cM at 4p15-p13, 1-59cM at 6p25-p21, 82-88cM at 17q23-q24, and 113-114cM at 17q25. For spine bone size, at effect sizes of 10% or greater, we excluded regions of 115-122cM at 1p31-p22, 136-141cM at 1p21, 207-260cM at 1q31-q42, 20-89cM at 4p16-q21, 11-21cM at 6p24-p23, and 1-6cM at 17p13. These results suggested that a number of candidate genes located in the excluded regions, such as the growth hormone (GH) gene, tumor necrosis factor-alpha (TNF-alpha) gene, and bone morphogenetic protein-3 (BMP3) gene, are unlikely to have a substantial effect on bone size variation in this Caucasian population.

Mapping quantitative trait loci for cross-sectional geometry at the femoral neck

A genome-wide linkage scan was performed in a sample of 79 multiplex pedigrees to identify genomic regions linked to femoral neck cross-sectional geometry. Potential quantitative trait loci were detected at several genomic regions, such as 10q26, 20p12-q12, and chromosome X.

INTRODUCTION

Bone geometry is an important determinant of bone strength and osteoporotic fractures. Previous studies have shown that femoral neck cross-sectional geometric variables are under genetic controls. To identify genetic loci underlying variation in femoral neck cross-sectional geometry, we conducted a whole genome linkage scan for four femoral neck cross-sectional geometric variables in 79 multiplex white pedigrees.

MATERIALS AND METHODS

A total of 1816 subjects from 79 pedigrees were genotyped with 451 microsatellite markers across the human genome. We performed linkage analyses on the entire data, as well as on men and women separately.

RESULTS

Significant linkage evidence was identified at 10q26 for buckling ratio (LOD = 3.27) and Xp11 (LOD = 3.45) for cortical thickness. Chromosome region 20p12-q12 showed suggestive linkage with cross-sectional area (LOD = 2.33), cortical thickness (LOD = 2.09), and buckling ratio (LOD = 1.94). Sex-specific linkage analyses further supported the importance of 20p12-q12 for cortical thickness (LOD = 2.74 in females and LOD = 1.88 in males) and buckling ratio (LOD = 5.00 in females and LOD = 3.18 in males).

CONCLUSIONS

This study is the first genome-wide linkage scan searching for quantitative trait loci underlying femoral neck cross-sectional geometry in humans. The identification of the genes responsible for bone geometric variation will improve our knowledge of bone strength and aid in development of diagnostic approaches and interventions for osteoporotic fractures.

Association and haplotype analyses of the COL1A2 and ER-alpha gene polymorphisms with bone size and height in Chinese

Bone size (BS) is another risk factor of fracture independent of BMD in determining bone strength, and height is highly related with BS. To test the effect of the estrogen receptor-alpha (ER-alpha) and collagen type I alpha 2 (COL1A2) genes on the variation of BS and height, we genotyped the PvuII and XbaI polymorphisms in the intron 1 of the ER-alpha gene and the MspI and (GT)n markers in the intron 47 and intron 1 of the COL1A2 gene in 400 Chinese nuclear families with a total of 1256 individuals. The BS at the hip and spine was measured using a Hologic QDR 2000 dual-energy X-ray absorptiometry (DXA) scanner. Population stratification, total-family association, and within-family association were used to test the relationship of BS (at the spine and hip) and height with the four polymorphisms. We also performed these association analyses with the haplotypes of the MspI and (GT)n polymorphisms in the COL1A2 gene, and with the haplotypes of the PvuII and XbaI markers in the ER-alpha gene. Weak within-family association was found between the COL1A2-MspI (P = 0.05) and the femoral neck BS, between the ER-alpha-PX (P = 0.04) and the intertrochanter BS, and between the COL1A2-(GT)(17) (P = 0.02), COL1A2-m(GT)(17) (P = 0.009) and height. Subsequent permutation tests generally confirmed the suggestive within-family association. For the weak within-family association, the proportions of phenotypic variance accounted by the COL1A2-MspI, ER-alpha-PX, COL1A2-(GT)(17), COL1A2-m(GT)(17) markers were 1.50%, 1.51%, 2.15%, and 2.43% for the corresponding phenotypes. The association results indicate that the (GT)n and MspI markers of COL1A2 gene may have some influence on the variation of both BS and height, and the XbaI and PvuII markers of ER-alpha gene may have some effect on the variation of height in Chinese but not on the variation of BS.