A genome-wide association study suggests that a locus within the ataxin 2 binding protein 1 gene is associated with hand osteoarthritis: the Treat-OA consortium

To identify the susceptibility gene in hand osteoarthritis (OA) the authors used a two-stage approach genome-wide association study using two discovery samples (the TwinsUK cohort and the Rotterdam discovery subset; a total of 1804 subjects) and four replication samples (the Chingford Study, the Chuvasha Skeletal Aging Study, the Rotterdam replication subset and the Genetics, Arthrosis, and Progression (GARP) Study; a total of 3266 people). Five single-nucleotide polymorphisms (SNPs) had a likelihood of association with hand OA in the discovery stage and one of them (rs716508), was successfully confirmed in the replication stage (meta-analysis p = 1.81×10⁻⁵). The C allele conferred a reduced risk of 33% to 41% using a case–control definition. The SNP is located in intron 1 of the A2BP1 gene. This study also found that the same allele of the SNP significantly reduced bone density at both the hip and spine (p<0.01), suggesting the potential mechanism of the gene in hand OA might be via effects on subchondral bone. The authors' findings provide a potential new insight into genetic mechanisms in the development of hand OA.

Genetic and environmental determinants on bone loss in postmenopausal Caucasian women: a 14-year longitudinal twin study

SUMMARY

This longitudinal twin study documented that genetic factors explain 44-56% of the between-individual variance in bone loss at femoral neck, lumbar spine, and forearm in postmenopausal Caucasian women, providing a rationale for identifying the specific genes involved.

INTRODUCTION

Although there is a significant genetic effect on peak BMD, until recently, no substantive studies on heritability of bone loss in human were available. The aim of the study was to estimate the heritability of the bone loss at multiple sites in postmenopausal Caucasian women.

METHODS

Postmenopausal female monozygotic (MZ) and dizygotic (DZ) twins aged 40 or above at baseline were selected from the TwinsUK registry and followed up for an average of 8 years (range 5-14 years). All twins were noncurrent hormone replacement therapy users and not on any osteoporosis treatment. They had dual-energy X-ray absorptiometry (DXA) scans of their hip, lumbar spine, and forearm several times (range 2-9) during the follow-up period. Individual bone losses at femoral neck, lumbar spine, and forearm were estimated by linear regression modeling. Structural equation modeling was utilized to estimate the heritability of the bone loss.

RESULTS

A total of 712 postmenopausal Caucasian female twins (152 MZ and 204 DZ pairs) were included. MZ twins were older and had slightly lower BMD at all sites than DZ twins. DZ twins had slightly higher bone loss at lumbar spine, but similar at femoral neck and forearm compared to MZ twins. Intraclass correlation coefficients (ICC) for the bone loss at all sites were significantly higher in MZ than DZ twin pairs (p = 0.0045, 0.0003, and 0.0007 for femoral neck, lumbar spine, and forearm, respectively), indicating a significant genetic influence on bone loss at these sites. After adjustment for age at baseline and weight change during the follow-up, the heritability estimate was 47% (95% CI 27-63%) for bone loss at femoral neck, 44% (95% CI 27-58%) for lumbar spine, and 56% (95% CI 44-65%) for forearm.

CONCLUSIONS

Our data suggest that up to 56% of the between-individual variance in bone loss is due to genes, providing a rationale to identify specific genetic factors for bone loss.

Natural history and risk factors for bone loss in postmenopausal Caucasian women: a 15-year follow-up population-based study

In this 15-year follow-up study, we found that the estimated rate of bone loss at the femoral neck (FN) for women aged 45-68 was linear at a rate of 1.67% per year, but quadratic for lumbar spine (LS) at a rate of 3.12% initially, and slowing down with age. We also confirmed the protective role of HRT, increasing weight, and lean mass in long-term bone loss.

INTRODUCTION

The objective was to describe the natural history of bone loss and explore the role of environmental factors in postmenopausal women over a 15-year period.

METHODS

Bone mineral density (BMD) at the FN and the LS were measured in postmenopausal women from the Chingford Study. Height, weight, HRT status, and calcium/vitamin D supplement were assessed at each visit. Osteoarthritis of hip and spine was assessed by X-ray at baseline and at year 8.

RESULTS

A total of 955 postmenopausal women with an average age of 54.7 at baseline were included. Both FN and LS BMD decreased significantly with age (p<0.0001). The decline was larger in the LS (-3.12% per year), which showed a quadratic relationship, than in the FN (-1.67% per year) with a linear relationship. The rate of bone loss was reduced by one third annually for the FN and LS respectively in current HRT users. Change in weight was positively associated with both DeltaFN and DeltaLS BMD (beta=0.16% and 0.09% change in DeltaFN and DeltaLS BMD per kilogramme change in weight respectively, p<0.0001 for both sites). Spine OA and progression were positively associated with DeltaLS BMD (beta=1.22% change in DeltaLS BMD per grade in spine OA and 0.45% change in DeltaLS BMD for patients who progressed, p<0.0001 for spine OA and p=0.002 for spine OA progression). Spine OA (beta=0.54% change in DeltaFN BMD per grade, p<0.0001), but not progression, and hip OA were positively associated with DeltaFN BMD. Furthermore, both age and body weight at baseline were positively associated with both DeltaFN and DeltaLS BMD (beta=0.02-0.04% change in DeltaFN and DeltaLS BMD per year increase in age at baseline and 0.004-0.007% change in DeltaFN and DeltaLS BMD per kilogramme increase in weight at baseline, all p<0.0001).

CONCLUSION

This large population-based longitudinal study demonstrated that the decline of BMD over 15 years is linear with age for the FN, but quadratic for the LS. The study confirmed the protective role of HRT, increased weight and lean mass in long-term bone loss.

Bone mineral density, osteoporosis, and osteoporotic fractures: a genome-wide association study

BACKGROUND

Osteoporosis is diagnosed by the measurement of bone mineral density, which is a highly heritable and multifactorial trait. We aimed to identify genetic loci that are associated with bone mineral density.

METHODS

In this genome-wide association study, we identified the most promising of 314 075 single nucleotide polymorphisms (SNPs) in 2094 women in a UK study. We then tested these SNPs for replication in 6463 people from three other cohorts in western Europe. We also investigated allelic expression in lymphoblast cell lines. We tested the association between the replicated SNPs and osteoporotic fractures with data from two studies.

FINDINGS

We identified genome-wide evidence for an association between bone mineral density and two SNPs (p<5x10(-8)). The SNPs were rs4355801, on chromosome 8, near to the TNFRSF11B (osteoprotegerin) gene, and rs3736228, on chromosome 11 in the LRP5 (lipoprotein-receptor-related protein) gene. A non-synonymous SNP in the LRP5 gene was associated with decreased bone mineral density (rs3736228, p=6.3x10(-12) for lumbar spine and p=1.9x10(-4) for femoral neck) and an increased risk of both osteoporotic fractures (odds ratio [OR] 1.3, 95% CI 1.09-1.52, p=0.002) and osteoporosis (OR 1.3, 1.08-1.63, p=0.008). Three SNPs near the TNFRSF11B gene were associated with decreased bone mineral density (top SNP, rs4355801: p=7.6x10(-10) for lumbar spine and p=3.3x10(-8) for femoral neck) and increased risk of osteoporosis (OR 1.2, 95% CI 1.01-1.42, p=0.038). For carriers of the risk allele at rs4355801, expression of TNFRSF11B in lymphoblast cell lines was halved (p=3.0x10(-6)). 1883 (22%) of 8557 people were at least heterozygous for these risk alleles, and these alleles had a cumulative association with bone mineral density (trend p=2.3x10(-17)). The presence of both risk alleles increased the risk of osteoporotic fractures (OR 1.3, 1.08-1.63, p=0.006) and this effect was independent of bone mineral density.

INTERPRETATION

Two gene variants of key biological proteins increase the risk of osteoporosis and osteoporotic fracture. The combined effect of these risk alleles on fractures is similar to that of most well-replicated environmental risk factors, and they are present in more than one in five white people, suggesting a potential role in screening.

Is telomere length in peripheral blood lymphocytes correlated with cancer susceptibility or radiosensitivity?

Mean terminal restriction fragment (TRF) lengths in white blood cells (WBCs) have been previously found to be associated with breast cancer. To assess whether this marker could be used as a test for breast cancer susceptibility in women, TRF length was measured in 72 treated female breast cancer patients and 1696 unaffected female controls between the ages of 45 and 77 from the Twin Research Unit at St Thomas' Hospital, as well as 140 newly diagnosed breast cancer cases and 108 mammographically screened unaffected controls from Guy's Hospital. Mean TRF was also tested for correlation with chromosome radiosensitivity and apoptotic response in the Guy's Hospital patients. After adjusting for age, smoking and body mass index, there was no significant difference in TRF lengths between the treated breast cancer patients and unaffected controls (P=0.71). A positive correlation between age-adjusted apoptotic response and mean TRF in newly diagnosed untreated breast cancer patients (P=0.008) was identified but no significant difference in TRF lengths between breast cancer patients and unaffected controls was detected (P=0.53). This suggests that TRF lengths in WBC, is not a marker of breast cancer susceptibility and does not vary significantly between affected women before and after treatment.

Lumbar disc disease shows linkage to chromosome 19 overlapping with a QTL for hand OA

OBJECTIVE

Cervical and lumbar degenerative disc disease (CDD and LDD, respectively) form part of the spine osteoarthritis (OA) phenotype and are known to be influenced by genetic factors. A genome-wide linkage analysis was performed to identify new chromosomal regions of interest.

METHODS

Dizygotic healthy female twin volunteers (n = 348) from the TwinsUK register who had magnetic resonance imaging scans 10 years ago coded for degenerative disease, were identified. Multipoint genome-wide linkage analysis was conducted using 737 highly polymorphic markers of approximate spacing 10 cM.

RESULTS

The mean age of the twins was 52 years. Significant linkage peaks (log of the odds (LOD) >3) were identified for LDD at three chromosomal regions. These included chromosome 1 (position 285 cM), chromosome 5 (position 175 cM) and chromosome 19 (position 80 cM). The peak on chromosome 19 had LOD = 4.06, and the empirical p = 6.7x10(-4) confirmed reliability of the linkage signal. It lies close to a linkage peak previously obtained by our group for hand OA.

CONCLUSIONS

This genome-wide linkage study of CDD and LDD shows evidence of linkage for LDD on chromosome 19. The region of interest is likely to harbour genes that are common to LDD and hand OA.

Association between KLOTHO gene and hand osteoarthritis in a female Caucasian population

OBJECTIVE

Osteoarthritis (OA) is a common complex disease with strong heritable components. In this study, we investigated the association between four putatively functional genetic variants in KLOTHO gene, a strong ageing-related gene, and hand OA in a large female Caucasian population.

METHODS

Subjects (n=1015, age range 33-74 years) were selected from the TwinsUK Registry. Radiographs of both hands were taken for each individual with standard posteroanterior view. The presence/absence of radiographic OA, osteophyte and joint space narrowing (JSN) was assessed using a standard atlas. Four putatively functional single nucleotide polymorphisms (SNPs) in KLOTHO gene were genotyped using allelic discrimination assay. Association was initially estimated using Pearson's chi(2) or Fisher's exact test at allelic and genotypic levels. The direction and magnitude of significant association were further investigated by robust logistic regression with age as a covariate.

RESULTS

We found significant association between SNP G-395A and the presence/absence of radiographic hand OA and osteophyte, but not JSN. Allele G significantly increased the risk for radiographic hand OA and osteophytes with odds ratios (ORs) of 1.44 (P=0.008, 95% confidence interval (CI) 1.09-1.91) and 1.36 (P=0.006, 95% CI 1.09-1.70), respectively. From logistic regression modelling, genotype GG showed more than three-fold increased risk for both radiographic hand OA (OR=3.10, 95% CI 1.10-8.76) and osteophyte (OR=3.10, 95% CI 1.10-8.75) when compared to genotype AA. After adjustment for age, ORs for genotype GG further increased to 4.39 (P=0.006, 95% CI 1.51-12.74) for radiographic hand OA and to 4.47 (P=0.005, 95% CI 1.56-12.77) for osteophytes.

CONCLUSIONS

Our results suggest that one variant in KLOTHO gene is associated with the susceptibility of hand OA and appears to act through osteophyte formation rather than cartilage damage.

Genetic influence on the progression of radiographic knee osteoarthritis: a longitudinal twin study

OBJECTIVE

Genetic influences on rates of osteoarthritis (OA) progression are unknown. Our aim was to estimate the heritability of progression of radiographic knee OA using a longitudinal twin study.

METHODS

Unselected monozygotic (MZ) and dizygotic (DZ) twin pairs from the TwinsUK registry were utilized. Anteroposterior radiographs were performed on both knees at baseline and follow-up using the same protocol. Radiographic features of knee OA including osteophyte and joint space narrowing (JSN) were assessed on a four-point scale using a standard atlas. Progression of knee osteophyte and JSN was defined as the difference in the corresponding score between follow-up and baseline > or =1. Liability threshold modelling using logistic regression was utilized for heritability estimation.

RESULTS

A total of 114 MZ pairs and 195 DZ pairs were studied. The average follow-up time was 7.2 years. Medial progression of osteophyte and JSN was more common than lateral progression. Prevalence of progression was generally higher in the MZs than the DZs. Similarly, concordances and tetrachoric correlations for both osteophyte and JSN were higher in the MZs than the DZs although only significant for overall and medial JSN and osteophyte. The heritability estimates were 69% [95% confidence interval (CI) 42-97%] and 80% (95% CI 50-100%) for medial osteophyte and JSN, respectively. The estimates were reduced by 7-15% after adjustment for age, body mass index (BMI), and the severity of osteophyte/JSN at baseline.

CONCLUSION

Our data documented a substantial genetic influence on the progression of knee OA--as seen in the medial compartment, providing a solid basis to search for genes involved in this highly relevant clinical trait.

The big finger: the second to fourth digit ratio is a predictor of sporting ability in women

BACKGROUND

The second to fourth finger length ratio (2d:4d) is thought to be related to diverse traits including cognitive ability, disease susceptibility, and sexuality.

OBJECTIVE

To examine the relationship between 2d:4d and sports ability in women.

METHODS

Hand radiographs from 607 women (mean age 54 years) were used to estimate 2d:4d. Ranking of sports ability was on a scale (1-5).

RESULTS

The highest achieved level of participation in any sport was significantly negatively associated with 2d:4d (b = -4.93, p = 0.01) as was the relationship between 2d:4d and running level (b = -6.81, p = 0.034). Ability in other sports also showed a negative relationship albeit non-significant.

CONCLUSIONS

These results suggest that a low 2d:4d ratio is related to increased female sports ability. It can be postulated that this ratio may predict potential sports ability. Understanding the mechanisms underpinning this relationship may give important insights into musculoskeletal fitness, health and disease.

Heritability of DNA-damage-induced apoptosis and its relationship with age in lymphocytes from female twins

Apoptosis is a physiological form of cell death important in normal processes such as morphogenesis and the functioning of the immune system. In addition, defects in the apoptotic process play a major role in a number of important areas of disease, such as autoimmune diseases and cancer. DNA-damage-induced apoptosis plays a vital role in the maintenance of genomic stability by the removal of damaged cells. Previous studies of the apoptotic response (AR) to radiation-induced DNA damage of lymphoid cells from individuals carrying germline TP53 mutations have demonstrated a defective AR compared with normal controls. We have also previously demonstrated that AR is reduced as individuals age. Results from the current study on 108 twins aged 18–80 years confirm these earlier findings that the AR of lymphoid cells to DNA damage is significantly reduced with increasing age. In addition this twin study shows, for the first time, that DNA-damage-induced AR has a strong degree of heritability of 81% (95% confidence interval 67–89%). The vital role of DNA-damage-induced apoptosis in maintaining genetic stability, its relationship with age and its strong heritability underline the importance of this area of biology and suggest areas for further study.