Confirmation of linkage to chromosome 1q for spine bone mineral density in southern Chinese

Association of handgrip strength with chronic diseases and multimorbidity: a cross-sectional study

The prevalence of chronic diseases has risen along with increased longevity. Co-occurrence of two or more chronic diseases in an individual (multimorbidity) is prevalent and poses a huge burden to individuals and the society. However, determinants of multimorbidity are largely unknown. Handgrip strength is a general indicator of muscle strength and linked with premature mortality. However, its role in multimorbidity has never been evaluated. To investigate the relationships between handgrip strength and multiple chronic diseases and multimorbidity, and to assess the usefulness of age and handgrip as a marker of chronic diseases and multimorbidity in a community dwelling sample of men and women, we analyzed a cross-sectional cohort with 1,145 subjects (748 men and 397 women) aged 50 years and older living in Hong Kong. Low handgrip strength was significantly associated with increased odds of having five and three chronic diseases in men and women, respectively, after controlling for age, body mass index, history of smoking, educational level, marital level and comorbidity. Multivariable-adjusted handgrip strength was significantly decreased with the number of chronic diseases in men (trend, P = 0.001), but the trend in women was marginal (trend, P = 0.06). Conversely, multivariable-adjusted age was significantly increased with the number of chronic diseases in women (trend, P = 0.033), but not in men (trend, P = 0.118). In conclusion, handgrip strength is associated with multiple chronic diseases and multimorbidity in men and women after adjustment of confounding factors. It shows a linear trend of association with the number of chronic diseases in men, but not in women. Since handgrip strength is a biomarker of multiple physiological systems, its augmentation may be a feasible strategy to improve general health and decrease likelihood of having multiple chronic diseases and hence, premature mortality.

Quantitative trait loci associated with the humoral innate immune response in chickens were confirmed in a cross between Green-Legged Partridgelike and White Leghorn

Natural antibodies (NA) create a crucial barrier at the initial steps of the innate humoral immune response. The main role of NA in the defense system is to bind the pathogens at early stages of infection. Different pathogens are recognized by the presence of highly conserved antigen determinant [e.g., lipopolysaccharide (LPS) in gram-negative bacteria or lipoteichoic acid (LTA) in gram-positive bacteria]. In chickens, a different genetic background of NA binds LPS and LTA antigens, encoded by different QTL. The main objective of this work was to confirm known QTL associated with LPS and LTA NA. For this purpose a chicken reference population was created by crossing 2 breeds: a commercial layer, White Leghorn, and a Polish indigenous chicken, Green-Legged Partridgelike. The chromosomal regions analyzed harbored to GGA3, GGA5, GGA6, GGA8, GGA9, GGA10, GGA14, GGA15, GGA18, and GGAZ. The data collected consisted of the NA titers binding LPS and LTA (determined by ELISA at 12 wk of age) as well as the genotypes (30 short tandem repeat markers; average of 3 markers/chromosome, collected for generations F(0), F(1), and F(2)). The analyses were performed with 3 statistical models (paternal and maternal half-sib, line cross, and linkage analysis and linkage disequilibrium) implemented in GridQTL software (http://www.gridqtl.org.uk/). The QTL study of humoral innate immune response traits resulted in the confirmation of 3 QTL associated with NA titers binding LPS (located on GGA9, GGA18, and GGAZ) and 2 QTL associated with NA titers binding LTA (located on GGA5 and GGA14). A set of candidate genes within the regions of the validated QTL has been proposed.

Suggestive linkage to chromosome 1q for bone mineral apparent density in Brazilian sister adolescents

OBJECTIVE

To investigate linkage to chromosome 1q and 11q region for lumbar spine, femoral neck and total body BMD and volumetric BMD in Brazilian sister adolescents aged 10-20-year-old and 57 mothers.

METHODS

We evaluated 161 sister pairs (n=329) aged 10-20 years old and 57 of their mothers in this study. Physical traits and lifestyle factors were collected as covariates for lumbar spine (LS), femoral neck (FN) and total body (TB) BMD and bone mineral apparent density (BMAD). We selected nine microsatellite markers in chromosome 1q region (spanning nearly 33cM) and eight in chromosome 11q region (spanning nearly 34cM) to perform linkage analysis.

RESULTS

The highest LOD score values obtained from our data were in sister pairs LS BMAD analysis. Their values were: 1.32 (P<0.006), 2.61 (P<0.0002) and 2.44 (P<0.0004) in D1S218, D1S2640 and D1S2623 markers, respectively. No significant LOD score was found with LS and FN BMD/BMAD in chromosome 11q region. Only TB BMD showed significant linkage higher than 1.0 for chromosome 11q region in the markers D11S4191 and D11S937.

DISCUSSION/CONCLUSIONS

Our results provided suggestive linkage for LS BMAD at D1S2640 marker in adolescent sister pairs and suggest a possible candidate gene (LHX4) related to adolescent LS BMAD in this region. These results reinforce chromosome 1q21-23 as a candidate region to harbor one or more bone formation/maintenance gene. In the other hand, it did not repeat for chromosome 11q12-13 in our population.

Identification of QTL genes for BMD variation using both linkage and gene-based association approaches

Low bone mineral density (BMD) is a risk factor for osteoporotic fracture with a high heritability. Previous large scale linkage study in Northern Chinese has identified four significant quantitative trait loci (QTL) for BMD variation on chromosome 2q24, 5q21, 7p21 and 13q21. We performed a replication study of these four QTL in 1,459 Southern Chinese from 306 pedigrees. Successful replication was observed on chromosome 5q21 for femoral neck BMD with a LOD score of 1.38 (nominal p value = 0.006). We have previously identified this locus in a genome scan meta-analysis of BMD variation in a white population. Subsequent QTL-wide gene-based association analysis in 800 subjects with extreme BMD identified CAST and ERAP1 as novel BMD candidate genes (empirical p value of 0.032 and 0.014, respectively). The associations were independently replicated in a Northern European population (empirical p value of 0.01 and 0.004 for CAST and ERAP1, respectively). These findings provide further evidence that 5q21 is a BMD QTL, and CAST and ERAP1 may be associated with femoral neck BMD variation.

Bone mineral density is linked to 1p36 and 7p15-13 in a southern Chinese population

Genome-wide linkage scans have identified a number of quantitative trait loci (QTLs) affecting bone mineral density (BMD), mainly in the Caucasian population. In this study, we aim to determine whether seven well-replicated QTLs also contribute to BMD variation in the southern Han Chinese population. Thirty-three microsatellite markers in the proximity of seven QTLs were genotyped in 1,459 subjects from 306 families ascertained through a proband with BMD Z-score equal to or less than -1.3 at either the lumbar spine or hip. Regression-based multipoint linkage analysis was performed. In the entire study population, good linkage evidence of total hip BMD to 7p14 [maximum log of odds (LOD) score (MLS) = 2.75; nominal P = 0.0002] and 1p36 (MLS = 1.6, P = 0.003) was revealed. In the subgroup analysis of 1,166 female subjects, MLS of 3.42, 2.65, 2.42, and 1.54 were obtained on 7p12 for total hip, lumbar spine, trochanter, and femoral neck BMD, respectively. A suggestive linkage signal was achieved at 7p14-15 with a MLS of 3.38 and 3.15 for trochanter and total hip BMD in the 678 premenopausal women, and at 7p12 for femoral neck and total hip BMD with MLS of 2.22 and 3.04 in postmenopausal women. Subgroup analysis of premenopausal women also provided additional evidence of suggestive linkage of total hip BMD to 1p36, with a MLS of 2.84 at 17.07 cM. Thus, linkage of BMD to 1p36 and 7p15-13 is confirmed in southern Chinese. Computational prioritization strategy and published genome-wide association studies suggested RERE and SFRP4 as two promising candidate genes in which variants responsible for the linkage signal may be identified by follow-up gene-wide association studies.

Genetic epidemiology of age-related osteoporosis and its clinical applications

Osteoporosis is an important and complex disorder that is highly prevalent worldwide. This disease poses a major challenge to modern medicine and its treatment is associated with high costs. Numerous studies have endeavored to decipher the pathogenesis of this disease. The clinical assessment of patients often incorporates information about a family history of osteoporotic fractures. Indeed, the observation of an increased risk of fracture in an individual with a positive parental history of hip fracture provides strong evidence for the heritability of osteoporosis. The onset and progression of osteoporosis are generally controlled by multiple genetic and environmental factors, as well as interactions between them, with rare cases determined by a single gene. In an attempt to identify the genetic markers of complex diseases such as osteoporosis, there has been a move away from traditional linkage mapping studies and candidate gene association studies to higher-density genome-wide association studies. The advent of high-throughput technology enables genotyping of millions of DNA markers in the human genome, and consequently the identification and characterization of causal variants and loci that underlie osteoporosis. This Review presents an overview of the major findings since 2007 and clinical applications of these genome-wide linkage and association studies.

Pre-B-cell leukemia homeobox 1 (PBX1) shows functional and possible genetic association with bone mineral density variation

Bone mineral density (BMD) is one of the major determinants of risk for osteoporotic fracture. Multiple studies reveal that peak bone mass is under strong genetic influence. One of the major susceptibility loci for peak spine BMD has been mapped to chromosome 1q21-q23 in the Caucasian population. We have previously replicated this finding in Southern Chinese pedigrees and detected a maximum multipoint log of odds (LOD) score of 2.36 in this region. To further fine-map this region, 380 single-nucleotide polymorphic (SNP) markers were genotyped in 610 sibpairs from 231 families. Several markers were identified in the association analysis as important candidates underlying BMD variation. Among them, successful replication was demonstrated for SNPs in pre-B-cell leukemia homeobox 1 (PBX1) gene in two other unrelated case-control cohorts. The functional role of PBX1 in bone metabolism was examined in vitro using human bone-derived cells (HBDC) and murine MC3T3-E1 pre-osteoblasts. PBX1 mRNA was constitutively expressed in both HBDC and MC3T3-E1 cells. Immunostaining revealed that PBX1 is localized in the nucleus compartment. Silencing of PBX1 by RNAi in MC3T3-E1 cells decreased the expression of Runx2 and Osterix, the critical transcription factors for osteogenesis, but accelerated cell proliferation and bone nodule formation. Overall, our data suggest a genetic and functional association of PBX1 with BMD.

Identification of LTBP2 on chromosome 14q as a novel candidate gene for bone mineral density variation and fracture risk association

CONTEXT

Low bone mineral density (BMD) is a major risk factor for osteoporotic fracture. Chromosome 14q has previously been linked to BMD variation in several genome-wide linkage scans in Caucasian populations.

OBJECTIVE

Our objective was to replicate and identify the novel candidate genes in the quantitative trait loci (QTL) at chromosome 14q QTL.

SUBJECTS AND METHODS

Eighteen microsatellite markers were genotyped for a 117-cM interval in 306 Southern Chinese pedigrees with 1459 subjects. Successful replication of the QTL was confirmed within this region for trochanter and total hip BMD. Using a gene prioritization approach as implemented in the Endeavour program, we genotyped 65 single-nucleotide polymorphisms in the top five ranking candidate genes within the linkage peak in 706 and 760 case-control subject pairs with extremely high and low trochanter and total hip BMD, respectively.

RESULTS

Single-marker and haplotype analyses revealed that ESR2 and latent TGF-beta binding protein 2 (LTBP2) had significant associations with trochanter and total hip BMD. Multiple logistic regression revealed a strong genetic association between LTBP2 gene locus and total hip BMD variation (P=0.0004) and prevalent fracture (P=0.01). Preliminary in vitro study showed differential expression of LTBP2 gene in MC3T3-E1 mouse preosteoblastic cells in culture.

CONCLUSIONS

Apart from ESR2, LTBP2 is a novel positional candidate gene in chromosome 14q QTL for BMD variation and fracture.

Molecular genetic studies of gene identification for osteoporosis

This review comprehensively summarizes the most important and representative molecular genetics studies of gene identification for osteoporosis published up to the end of September 2007. It is intended to constitute a sequential update of our previously published reviews covering the available data up to the end of 2004. Evidence from candidate gene-association studies, genome-wide linkage and association studies, as well as functional genomic studies (including gene-expression microarray and proteomics) on osteogenesis and osteoporosis, are reviewed separately. Studies of transgenic and knockout mice models relevant to osteoporosis are summarized. The major results of all studies are tabulated for comparison and ease of reference. 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.

A differential association of ALOX15 polymorphisms with bone mineral density in pre- and post-menopausal women

OBJECTIVE

The 12/15-lipoxygenase gene ALOX15 is reported to be a negative regulator of BMD in knockout mice. Nonetheless results are controversial as over-expression of ALOX15 protects against inflammation-related bone loss. The aim of the present study is to systematically study the relation of ALOX15 polymorphisms in BMD variation in southern Chinese women.

METHODS

Ten tag single nucleotide polymorphisms (SNP) were genotyped in 942 subjects with either low BMD (defined by a BMD Z score < or =-1.28 at either the hip or spine) or high BMD (Z score > or =+1). Single locus and haplotype associations were performed using logistic regression with adjustment of age, height and weight.

RESULTS

The variant 'G' allele of rs2619112 was associated with a reduced risk of low BMD at the femoral neck in pre-menopausal women (OR = 0.442, p = 0.007) but an increased risk in post-menopausal women (OR = 1.727, p = 0.042). Haplotype analysis revealed findings similar to the single locus tests.

CONCLUSION

The variant alleles of rs2619112 and rs916055 and their haplotypes of ALOX15 are associated with high BMD in pre-menopausal women but low BMD in post-menopausal women. This suggests that ALOX15 is a dual modulator of BMD variation with opposing effects in pre- and post-menopausal women.