Genome studies and linkage in primary osteoarthritis

Evolution and advancements in genomics and epigenomics in OA research: How far we have come

OBJECTIVE

Osteoarthritis (OA) is the most prevalent musculoskeletal disease affecting articulating joint tissues, resulting in local and systemic changes that contribute to increased pain and reduced function. Diverse technological advancements have culminated in the advent of high throughput "omic" technologies, enabling identification of comprehensive changes in molecular mediators associated with the disease. Amongst these technologies, genomics and epigenomics - including methylomics and miRNomics, have emerged as important tools to aid our biological understanding of disease.

DESIGN

In this narrative review, we selected articles discussing advancements and applications of these technologies to OA biology and pathology. We discuss how genomics, deoxyribonucleic acid (DNA) methylomics, and miRNomics have uncovered disease-related molecular markers in the local and systemic tissues or fluids of OA patients.

RESULTS

Genomics investigations into the genetic links of OA, including using genome-wide association studies, have evolved to identify 100+ genetic susceptibility markers of OA. Epigenomic investigations of gene methylation status have identified the importance of methylation to OA-related catabolic gene expression. Furthermore, miRNomic studies have identified key microRNA signatures in various tissues and fluids related to OA disease.

CONCLUSIONS

Sharing of standardized, well-annotated omic datasets in curated repositories will be key to enhancing statistical power to detect smaller and targetable changes in the biological signatures underlying OA pathogenesis. Additionally, continued technological developments and analysis methods, including using computational molecular and regulatory networks, are likely to facilitate improved detection of disease-relevant targets, in-turn, supporting precision medicine approaches and new treatment strategies for OA.

Association of IL-17A-197G/A and IL-17F-7488T/C polymorphisms and osteoarthritis susceptibility: A meta-analysis

AIM

This meta-analysis was conducted with the aim of collecting and synthesizing the existing evidence on the association of interleukin-17A (IL-17A)-197G/A and IL-17F-7488T/C gene polymorphisms and osteoarthritis (OA) susceptibility.

METHODS

Six electronic databases including PubMed, EMBASE, Web of Science, Cochrane Library, CNKI, and Wanfang were systematically searched for potentially relevant studies previous to June 2019. The strengths of association were estimated by summary odds ratios (ORs) and 95% confidence intervals (95%CIs) in a model-free approach. Heterogeneity test and sensitivity analysis were also conducted to guarantee the reliability of this study.

RESULTS

Six eligible case-control studies comprising 1989 OA patients and 2116 healthy controls were obtained for the meta-analysis. Dominant model was confirmed to be the optimal genetic model (MM + Mm vs mm). The pooled estimate supported that IL-17A-197G/A and IL-17F-7488T/C polymorphisms were significantly associated with OA susceptibility in the overall population (IL-17A-197G/A: GG + GA vs AA, OR = 0.69, 95%CI 0.57-0.80; P < .001; IL-17F-7488T/C, TT + TC vs CC, OR = 0.46, 95%CI 0.29-0.71, P < .001). However, subgroup analyses suggested the association only existed in Asians and knee OA.

CONCLUSION

The findings of the present study indicate that IL-17A-197G/A and IL-17F-7488T/C polymorphisms are positively associated to reduced risk of knee OA, especially in Asian populations.

Association between ADAM12 Single-Nucleotide Polymorphisms and Knee Osteoarthritis: A Meta-Analysis

Objective

ADAM12 polymorphisms may be associated with the risk of knee osteoarthritis (KOA), but currently available evidence remains controversial. We performed this meta-analysis to confirm whether ADAM12 polymorphisms were associated with susceptibility of KOA.

Methods

A comprehensive literature search in PubMed, EMBASE, and ISI Web of Science was conducted to identify observational studies assessing the association between ADAM12 polymorphisms and susceptibility of KOA. The strength of association was indicated as odds ratio (OR) and the corresponding 95% confidence interval (95%CI). Four types of genetic model (additive model, dominant model, recessive model, and allele model) were evaluated for each included study. Subgroup analysis by ethnicity was performed.

Results

Seven case-control studies comprising a total of 3512 KOA patients and 5405 healthy controls were included in the meta-analysis. A significant association between rs1871054 and increased KOA risk was found in each genetic model. No significant association was found between KOA and rs3740199, rs1044122, or rs1278279 in any genetic model.

Conclusion

Based on the findings of our study, there was a modest but statistically significant association between rs1871054 and risk of KOA in Asian population, while other polymorphisms (rs3740199, rs1044122, or rs1278279) in ADAM12 were not associated with KOA in any population.

IL1R1 gene polymorphisms are associated with knee osteoarthritis risk in the Chinese Han population

IL1R1, encoding interleukin 1 receptor type 1, is located in the IL-1 gene cluster and is involved in the pathogenesis of hand, hip, and knee osteoarthritis (OA) in different ethnicities. However, the link between IL1R1 polymorphisms and OA risk in the Chinese Han population is unknown. We studied the association between five IL1R1 polymorphisms (rs10490571, rs12712127, rs956730, rs3917225, and rs3917318) and OA risk by analyzing the genotypes of 298 knee OA patients and 297 controls using Sequenom MassARRAY technology. Logistic regression analysis after adjusting for gender and age revealed significant differences in the allele frequencies of IL1R1 rs956730 and IL1R1 rs3917225 between patients and controls. In addition, IL1R1 rs3917225 was associated with increased risk of knee OA with or without adjustment by age and gender in the dominant model (adjusted OR= 1.47, 95%CI: 1.04-2.07, P = 0.030), the recessive model (adjusted OR= 1.75, 95%CI: 1.08-2.85, P= 0.023), and the additive model (adjusted OR= 1.40, 95%CI: 1.09-1.79, P = 0.007). This study is the first to report that IL1R1 polymorphisms are associated with knee OA susceptibility in the Northwestern Chinese Han population.

DVWA gene polymorphisms and osteoarthritis

BACKGROUND

Osteoarthritis (OA) is a degenerative joints disorder influenced by genetic predisposition. We reported that rs11718863 DVWA SNP was represented in Sicilian with a more severe Kellgren and Lawrence (KL) radiographic grade, displaying its predictive role as OA marker progression. Here, we describe the DVWA SNPs: rs11718863, rs7639618, rs7651842, rs7639807 and rs17040821 probably able to induce protein functional changes.

FINDINGS

Sixty-one Sicilian patients with knee OA and 100 healthy subjects were enrolled. Clinical and radiographic evaluation was performed using AKSS scores and KL. Linkage Disequilibrium (LD) analyses were performed in order to verify whether the SNPs segregate as haplotype. All DVWA SNPs'MinorAllele Frequencies (MAF) were greater than in the European. The rs7639618 SNP showed a statistical association with KL. Our analyses show that a LD exists among rs11718863 and rs7639618, as well as between rs7651842, rs7639807 and rs17040821 SNPs. We also observed that three out of the 161 individuals investigated were simultaneously homozygous carriers of the rs7651842, rs7639807 and rs17040821 MAF alleles.

CONCLUSIONS

In summary, the purpose of this preliminary research was to highlight possible associations between DVWA SNPs and OA clinical and radiographic data. This work represents a multidisciplinary medicine approach to study OA where clinical, radiological and genetic evaluation could contribute to better define OA grading.

Association of PPARγ gene polymorphisms with osteoarthritis in a southeast Chinese population

Primary osteoarthritis (OA) is a leading cause of disability in developed countries. Currently no satisfactory treatment to stop disease progression exists. Recent studies suggest that activation of the transcription factor peroxisome proliferator-activated receptor gamma (PPARγ) is an interesting therapeutic target for this disease. PPARγ is a transcription factor important for adipogenesis and adipocyte differentiation. Agonists of PPARγ inhibit inflammation and reduce generation of cartilage degradation products both in vitro and in vivo, and reduce the development/progression of cartilage lesions in OA animal models. However, there are no studies to assess the role of PPARγ in OA susceptibility of human peripheral joints in a Chinese population. We conducted a case-control study in a southeast Chinese population to determine the association of PPARγ gene polymorphisms (rs1801282, rs12629751, rs2292101, rs4135275 and rs1175543) with OA. One-hundred knee OA cases and 100 controls were studied. Statistically significant differences were detected in genotype and allele frequencies between OA and control groups in this population. For knee OA, the highest risk was associated with the variant allele T of the single nucleotide polymorphism rs12629751 (odds ratio (OR): 0.341, 95% confidence interval (CI):0.173-0.673, P = 0.002), and allele T of SNP rs12629751 (chi-square: 9.546, P = 0.002) could be considered as a risk factor of knee OA. Therefore, PPARγ mutation could be associated with the incidence of OA in a Chinese population. There is a significant association between the PPARγ polymorphism rs12629751 and susceptibility to knee OA in a southeast Chinese population.

Genetic, clinical and radiographic signs in knee osteoarthritis susceptibility

INTRODUCTION

Osteoarthritis (OA) is considered to be a multifactorial and polygenic disease and diagnosis is mainly clinical and radiological. Correlation between radiographic data and clinical status has been reported. However, very few studies, especially in Caucasian people, describe the association between the Kellgren and Lawrence OA grading scale (KL) and genetic alterations to better understand OA etiopathogenesis and susceptibility. In order to update the knee OA grading, in this study we assessed the associations between KL grade, clinical features such as American Knee Society Score (AKSS), age, and polymorphisms in the principal osteoarthritis susceptibility (OS) genes in Sicilian individuals.

METHODS

In 66 Sicilian individuals affected by primary knee OA, the clinical and radiographic evaluation was performed using 2 sub-scores of AKSS (knee score (KS) and function score (FS)) and KL. The patients were also classified according to age. Online Mendelian Inheritance in Man (OMIM) and Database of Single Nucleotide Polymorphisms (dbSNP) Short Genetic Variations databases were used to select gene regions containing the following polymorphisms to analyze: FRZB rs288326 and rs7775, MATN3 rs77245812, ASPN D14 repeats, PTHR2 rs76758470, GDF5 rs143383 and DVWA rs11718863. Patient genotypes were obtained using Sanger DNA sequencing analysis.

RESULTS

In our cohort of patients a statistical association between the variables analyzed was reported in all associations tested (KL versus KS, FS and age). We observed that a mild to severe OA radiographic grade is related to severe clinical conditions and loss of articular function and that the severity of symptoms increases with age. Concerning the genotyping analysis, our results revealed a significant statistical association between KL grading and GDF5 rs143383 and DVWA rs11718863 genetic alterations. The latter was also associated with a more severe radiographic grade, displaying its predictive role as OA marker progression. Statistically significant association between clinical, radiographic and genetic signs observed, suggests extending the actual grading of knee OA based mainly on X-ray features.

CONCLUSIONS

This work represents a multidisciplinary and translational medicine approach to study OA where clinical, radiological, and OS5 and OS6 SNPs evaluation could contribute to better define grading and progression of OA and to the development of new therapies.

Relationship between vitamin D receptor gene (VDR) polymorphisms, vitamin D status, osteoarthritis and intervertebral disc degeneration

The vitamin D endocrine system is involved in bony and cartilaginous metabolisms and alterations in the homeostasis of this system could be associated to pathological conditions of cartilaginous tissue. In this context, the presence of polymorphisms in the vitamin D receptor gene (VDR), in association with the susceptibility to common osteochondral diseases, was largely investigated. The aim of this review was to summarize data present in literature, analyzing the association of the VDR polymorphisms, vitamin D status and knee cartilage and intervertebral disc pathologies, trying to suggest links between the different specific pathologies analyzed. Concerning the association between VDR polymorphisms and cartilaginous tissue diseases, we found controversial reports. However, the great majority of papers reported an association with lumbar disc degeneration, whereas about half of the studies found an association with osteoarthritis. A further association between VDR polymorphisms (in linkage disequilibrium) and the presence of specific characteristics of these diseases, in particular the formation of osteophytes, was evidenced. Finally, the influence of vitamin D status on these pathologies was evaluated, trying to evidence the relation between the presence of particular genetic variants in the VDR and vitamin D levels or to show whether a particular vitamin D status could predispose to the development or progression of such diseases, however, no significant associations were found. In the future, given the role of vitamin D system in the cartilaginous tissue metabolism, it could be interesting to perform functional and tissue specific studies to analyze the interplay between the different VDR variants and its ligand.

Association of a functional polymorphism in the promoter region of TLR-3 with osteoarthritis: a two-stage case-control study

Recent studies have suggested that polymorphisms in toll-like receptor 9 (TLR-9), an endosomal TLR, are associated with knee osteoarthritis (OA). TLR-3, -7, and -8 are also found on the surface of endosomes and to investigate whether similar associations exist with polymorphisms in these TLR genes we performed a two-stage case-control study and genotyped 11 TLR single nucleotide polymorphisms (SNPs) in 823 OA cases and 594 healthy controls by polymerase chain reaction restriction fragment length polymorphism assays. Real-time PCR was performed to assess the functional expression of an identified promoter polymorphism in TLR-3 following dexamethasone stimulation of articular chondrocytes. An association between TLR-3 SNPs at rs3775296 and rs3775290 and OA was identified in both populations. In males the allelic frequencies of TLR-7 rs179010 and TLR-8 rs5744080 were significantly different between OA cases and healthy controls. The ATCA, CTCA, and CCTA haplotypes of TLR-3 were associated with OA susceptibility. A significant difference in TLR-3 gene expression following dexamethasone treatment was seen among the various genotypes of rs3775296 (p = 0.004). Our findings indicate that a SNP in the promoter region of TLR-3 is associated with elevated TLR-3 gene expression and susceptibility to knee OA in a Chinese Han population.

The genetics and functional analysis of primary osteoarthritis susceptibility

Recent genome-wide association scans (GWASs) along with several adequately powered candidate gene studies have yielded a number of risk alleles for osteoarthritis (OA). This number is now sufficiently large to allow conclusions to be drawn regarding the nature of genetic susceptibility, including the fact that the risk alleles have variable effects depending on sex, ethnicity and on the skeletal site of the disease. Several of the alleles that have emerged from the GWASs are within or close to highly plausible candidate genes, including RUNX2 and CHST11. However, the majority of risk alleles do not map to genes previously reported to play a role in musculoskeletal biology, indicating that the GWAS datasets are telling us something new about the OA disease process. Functional studies have so far revealed that effects on gene expression are likely to be one of the main mechanisms through which OA susceptibility is acting. Epigenetic mechanisms such as DNA methylation also influence OA risk, and integration of genetic, transcriptomic and epigenetic data will allow us to use the genetic discoveries for informed development of new OA biological treatments.

Genetic association analysis of GDF5 and ADAM12 for knee osteoarthritis

OBJECTIVES

To examine two single-nucleotide polymorphisms (SNPs) for their association with knee osteoarthritis (OA) susceptibility in Korean cohort.

METHODS

Two thousand four hundred and sixty-two subjects aged 50 years and older were assessed for OA at the knee, were genotyped with two SNPs (GDF5; rs143383 and ADAM12; rs3740199). Radiographs were read by two examiners that used an atlas of radiographic features to obtain a global Kellgren/Lawrence (K/L) score. Genomic DNA was extracted from peripheral blood using a QIAamp DNA Blood Mini Kit. GDF5 genotyping was performed by high resolution melting analysis. ADAM12 genotyping was performed by TaqMan assay. The allele frequencies were assessed by counting alleles. Associations were tested by calculating the odds ratios (ORs) and 95% confidence intervals (95% CIs), using logistic regression analysis with adjustments for age, gender and body mass index (BMI).

RESULTS

Of this cohort, 725 subjects had radiographic OA (defined as a K/L score of ≥ 2). The mean age of the OA patients (females: 76.4%) was 67.4 (7.9) years. In GDF5, we observed a T-allele frequency of 74.1% in our controls, compared with that of 73.7% in patients (P = 0.72; OR 0.97, 95% CI; 0.83-1.13). In ADAM12, the frequency of G-allele in the case (54.6%) versus the control (55.0%) was calculated (P = 0.94, OR 1.01, 95% CI; 0.88-1.15). There was no significant difference in the genotype frequencies between the patients and healthy controls.

CONCLUSION

The associations of two SNPs with OA that were noted in previous studies, were not found in the Korean OA cohort.

Association study of the candidate gene for knee osteoarthritis in Koreans

The aim of this study was to examine a single-nucleotide polymorphism (SNP) rs7639618 of double von Willebrand factor (DVWA) gene for the association with osteoarthritis (OA) susceptibility in Korean cohort. The study was a part of the Korean cohort study. Two thousand four hundred sixty-two subjects aged 50 years and older who were derived from the cohort and who were assessed for OA at the knee were genotyped. The anteroposterior extended-view weight-bearing radiographs of the knees were obtained. Of the subjects, 725 subjects had radiographic OA. Genomic DNA was extracted from peripheral blood using a QIAamp DNA Blood Mini Kit (Qiagen, Valencia, CA). Genotyping was performed using High Resolution Melt or the Taq-Man allelic discrimination assay and the Rotor-Gene 6000 (Corbett Research, Sydney,Australia). Associations were tested by calculating the odds ratios (ORs) and 95% confidence intervals (95% CIs), using logistic regression analysis with adjustments for age, gender, and body mass index (BMI). The mean age of the OA patients (females: 554 subjects, 76.4%) was 67.4 (7.9) years. The intraobserver agreement was high for the identification of osteophytes (κ: 0.80) and joint space narrowing (κ: 0.70). There was no significant difference (all P values > 0.05) in the genotype or allele frequencies between the patients with OA and healthy controls. There was also no significant difference when the cases were adjusted by age, gender, and BMI. The associations of DVWA SNPs with OA were noted in previous studies and were not found in the Korean OA cohort.

Hip osteoarthritis susceptibility is associated with IL1B -511(G>A) and IL1 RN (VNTR) genotypic polymorphisms in Croatian Caucasian population

Among the predisposing factors to osteoarthritis (OA), a frequent destructive joint disease, is the complex genetic heritage including the interleukin-1 family members like the IL1β (IL1B) and the IL1 receptor antagonist (IL1RN) genes. The aim of this study was to investigate allelic and genotypic frequencies of the IL1B gene single nucleotide polymorphism (SNP) at -511(G>A) and the variable number tandem repeat (VNTR) in the IL1RN gene in a Croatian Caucasian population of hip OA (HOA) cases and healthy controls. A total of 259 HOA patients with total hip replacement (THR) and 518 healthy blood donors as controls were genotyped for IL1B gene SNP -511(G>A) and the VNTR in the IL1RN gene associated with HOA. The genotype G/A (1/2) at IL1B was significantly associated with the protection of the HOA (p < 0.036, OR = 0.72, 95% CI = 0.52-0.99). The genotype G/G (1/1) had only a trend towards the susceptibility (p = 0.053, OR = 1.35, 95% CI = 0.98-1.86) to disease. None of the haplotypes IL1B -511(G>A) and IL1RN (VNTR) were found associated with the HOA. The haplotype 1-2 at these loci had only a trend to susceptibility (p = 0.065). Haplotype 1-3 had a significant male bias in diseased. Furthermore, genotype comprising 2-1/2-2 haplotypes was found significantly associated with predisposition to HOA (p = 0.027, OR = 2.23, 95% CI = 1.03-4.88), whereas genotype 1-1/2-2 with protection to disease (p = 0.028, OR = 0.65, 95% CI = 0.43-0.97). Our findings suggest that HOA in Croatian population might have a different genetic risk regarding the IL1 locus than has been reported for other Caucasian populations previously.

Dual function of β-catenin in articular cartilage growth and degeneration at different stages of postnatal cartilage development

PURPOSE

The objective of this study was to determine the role of β-catenin in normal postnatal articular cartilage growth and degeneration.

METHODS

We investigated β-catenin gene and protein expression in hip cartilage cells of normal Wistar rats at two, four, six and eight weeks of age by using reverse transcriptase polymerase chain reaction (RT-PCR) and immunohistochemistry. Primary articular chondrocytes from eight week old rats were cultured and treated with LiCl for activation of β-catenin. Collagen X and matrix metalloproteinase 13 (MMP-13) were detected by quantitative RT-PCR and immunofluorescence. A disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)-4 and 5 were detected by quantitative RT-PCR, and terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) was used for detecting cell apoptosis.

RESULTS

The highest levels of β-catenin expressions were detected in two week old rats, after which a steady decline was observed over the remaining period of observation (p < 0.05). When primary articular chondrocytes from eight week old rats were treated with LiCl, β-catenin mRNA and protein were induced (p < 0.05). Moreover, LiCl-activated β-catenin in chondrocytes was associated with significant concomitant increases in mRNA expression of collagen X and the MMP-13 encoding collagenase 3. Significantly increased mRNA expression of ADAMTS-5 was also seen in primary chondrocytes from eight week old rats after LiCl treatment (p < 0.05). The effect was specific to ADAMTS-5 since ADAMTS-4, which has similar proteolytic activity but different aggrecanase activity, was unaffected. Finally, TUNEL staining revealed that LiCl-activated β-catenin signalling led to increased cell apoptotic events in chondrocytes (p < 0.05).

CONCLUSIONS

Our findings suggest that normal spatiotemporal patterns and degrees of Wnt/β-catenin signalling are needed to maintain postnatal articular cartilage growth and function. In the early stages of cartilage development, activation of β-catenin signalling is necessary for articular cartilage growth, while in adult cartilage it leads to degeneration and osteoarthritic-like chondrocytes.

Prevalence of the Pro12Ala missense mutation in the PPARG2 gene in Kuwaiti patients with primary knee osteoarthritis

BACKGROUND AND OBJECTIVES

Peroxisome proliferator-activated receptors (PPARs) play an important role in a number of cellular and metabolic functions. This study was carried out to determine the prevalence of a missense mutation (Pro12Ala) in the PPARG2 gene in Kuwaiti Arab patients with primary knee osteoarthritis (OA) and healthy controls with the aim of identifying a possible association.

DESIGN AND SETTING

A prospective cross-sectional study carried out at three major teaching hospitals (referral centers) in the country over a one-year period.

PATIENTS AND METHODS

The prevalence of PPARG2 gene Pro12Ala missense mutation was determined in 104 Kuwaiti Arab patients with primary knee OA and 111 ethnically matched healthy controls. The prevalence of this Pro12Ala missense mutation was also determined in clinical subgroups of OA patients divided on the basis of age at onset, function and radiologic grading.

RESULTS

The Pro-Pro genotype of the PPARG2 gene Pro12Ala missense mutation was detected in 95/104 (91.3%) cases compared to 111/111 (100%) in the control subjects. The heterozygous Pro-Ala genotype was detected in 9/104 (8.7%) of the OA patients, while it was not detected in any of the controls. The Ala-Ala genotype was not detected in any of the OA patients or the controls. No significant differences were detected in the PPARG2 gene Pro12Ala genotypes in the subgroups of patients classified on the basis of age at onset, functional assessment using Lequesne's functional index, and radiological grading using Kellgren-Lawrence (K-L) grading.

CONCLUSIONS

This study found no significant association between the PPARG2 gene Pro12Ala missense mutation and knee OA. However, the presence of the Pro-Pro genotype of the PPARG2 gene mutation has a protective effect against development of OA.

Beta-catenin, cartilage, and osteoarthritis

The early cellular events during the development of osteoarthritis (OA) are accelerated articular chondrocyte maturation and extracellular matrix degradation, which are usually seen in the weight-bearing region of articular cartilage. The results of our recent studies from transgenic OA mouse models indicate that upregulation of beta-catenin signaling in articular chondrocytes is most likely responsible for the conversion of normal articular chondrocytes into maturing (arthritic) chondrocytes, which is associated with activation of chondrocyte maturational genes and matrix degradation. Conditional activation of the beta-catenin gene in articular chondrocytes leads to an OA-like phenotype. Overexpression of Smurf2, an E3 ubiquitin ligase, also induces an OA-like phenotype through upregulation of beta-catenin signaling. In addition, beta-catenin upregulation was also found in articular cartilage tissues in patients with OA. These findings indicate that beta-catenin plays a central role in articular cartilage function and that activation of beta-catenin signaling may represent a pathologic mechanism for OA development.

Interleukin-1 region meta-analysis with osteoarthritis phenotypes

OBJECTIVE

Several research groups have examined osteoarthritis (OA) association with Interleukin-1 (IL-1) region markers and haplotypes. The results have been suggestive for hand OA, negative for knee OA, and conflicting for hip OA.

DESIGN

Our aim was to address conflicts employing meta-analytical methods on data from 1238 European-descent cases with various OA phenotypes and 1269 European-descent controls from four study centers. We imputed some missing genotype data and reconstructed IL-1 region extended haplotypes. A previously reported 7-marker IL1A-IL1B-IL1RN extended risk haplotype was tested for association with each specific index phenotype.

RESULTS

For hip OA, data from three centers showed heterogeneity of extended-risk-haplotype effect, two panels showing trend toward risk and another showing protection, with overall odds ratio (OR) 1.24 (95% Confidence interval (CI) 0.45-3.41, P 0.67). The heterogeneity fell partly along control ascertainment lines, chiefly between controls ascertained as spouses of arthroplasty patients and controls identified through population radiographic survey. For knee OA, the results showed no heterogeneity and no significant extended-risk-haplotype effect. For hand OA, the results showed little heterogeneity and a modest trend toward positive association (summary OR 1.34, 95% CI 0.83-2.17 P 0.23). Using a Bayesian partition modeling approach, the 7-marker extended haplotypes showed no significant effect on any OA phenotype examined. A 3-single-nucleotide polymorphism (SNP) IL1B-IL1RN haplotype rs1143627-rs16944-rs419598 showed a trend toward hand OA association (posterior probability of association 0.72) with the most prominent feature being protection from a specific haplotype representing a partial mirror image of the extended risk haplotype (OR estimated at 0.46).

CONCLUSIONS

The meta-analysis data do not confirm but only suggest that some hand and hip OA risk could be associated with the IL-1 region, particularly centered in IL1B and possibly also IL1RN.

Association Between Interleukin 1 Gene Cluster Polymorphisms and Bilateral Distal Interphalangeal Osteoarthritis

Objective.

To examine the association of the interleukin 1 gene (IL1) cluster polymorphisms and their haplotypes with bilateral distal interphalangeal joint osteoarthritis (DIP OA).

Methods.

Radiographs of both hands of 295 dentists and 248 teachers were examined and classified for the presence of OA using reference images. Bilateral DIP OA was defined by the presence of radiographic findings of grade 2 or more in at least 1 symmetrical pair of the DIP joints. We genotyped 10 single-nucleotide polymorphisms (SNP) in theIL1R1, IL1RL2, IL1A, IL1B,andIL1RNgenes using polymerase chain reaction-based methods. Haplotypes were statistically reconstructed using the PHASE program. The association between the genotypes/diplotypes and bilateral DIP OA was examined with logistic regression analysis.

Results.

TwoIL1BSNP (rs1143634 and rs1143633) were associated with bilateral DIP OA. The carriers of theIL1Brs1143634 minor allele had an increased OA risk [odds ratio (OR) 1.6; 95% confidence interval (CI) 1.08–2.26] compared to the noncarriers. The association was stronger in the dentists. The distribution of theIL1Brs1143633 genotype fit a recessive mode of inheritance (OR 3.03, 95% CI 1.35–6.83, p = 0.006). TwoIL1B-IL1RNextended haplotype alleles (211-1 and 121-1) were associated with bilateral DIP OA. An interaction between theIL1Brs1143634 and theIL1R1-IL1RL2andIL1B-IL1RNextended haplotypes and occupation (increased risk of OA among dentists only) was observed.

Conclusion.

Our results provide further evidence for the role ofIL1gene cluster polymorphisms in the etiology of OA and suggest that some of these may predispose DIP joints to the effects of mechanical overload.

Activation of beta-catenin signaling in articular chondrocytes leads to osteoarthritis-like phenotype in adult beta-catenin conditional activation mice

Osteoarthritis (OA) is a degenerative joint disease, and the mechanism of its pathogenesis is poorly understood. Recent human genetic association studies showed that mutations in the Frzb gene predispose patients to OA, suggesting that the Wnt/beta-catenin signaling may be the key pathway to the development of OA. However, direct genetic evidence for beta-catenin in this disease has not been reported. Because tissue-specific activation of the beta-catenin gene (targeted by Col2a1-Cre) is embryonic lethal, we specifically activated the beta-catenin gene in articular chondrocytes in adult mice by generating beta-catenin conditional activation (cAct) mice through breeding of beta-catenin(fx(Ex3)/fx(Ex3)) mice with Col2a1-CreER(T2) transgenic mice. Deletion of exon 3 of the beta-catenin gene results in the production of a stabilized fusion beta-catenin protein that is resistant to phosphorylation by GSK-3beta. In this study, tamoxifen was administered to the 3- and 6-mo-old Col2a1-CreER(T2);beta-catenin(fx(Ex3)/wt) mice, and tissues were harvested for histologic analysis 2 mo after tamoxifen induction. Overexpression of beta-catenin protein was detected by immunostaining in articular cartilage tissues of beta-catenin cAct mice. In 5-mo-old beta-catenin cAct mice, reduction of Safranin O and Alcian blue staining in articular cartilage tissue and reduced articular cartilage area were observed. In 8-mo-old beta-catenin cAct mice, cell cloning, surface fibrillation, vertical clefting, and chondrophyte/osteophyte formation were observed. Complete loss of articular cartilage layers and the formation of new woven bone in the subchondral bone area were also found in beta-catenin cAct mice. Expression of chondrocyte marker genes, such as aggrecan, Mmp-9, Mmp-13, Alp, Oc, and colX, was significantly increased (3- to 6-fold) in articular chondrocytes derived from beta-catenin cAct mice. Bmp2 but not Bmp4 expression was also significantly upregulated (6-fold increase) in these cells. In addition, we also observed overexpression of beta-catenin protein in the knee joint samples from patients with OA. These findings indicate that activation of beta-catenin signaling in articular chondrocytes in adult mice leads to the premature chondrocyte differentiation and the development of an OA-like phenotype. This study provides direct and definitive evidence about the role of beta-catenin in the development of OA.

Vitamin D receptor TaqI, BsmI and ApaI polymorphisms and osteoarthritis susceptibility: a meta-analysis

OBJECTIVE

Genetic factors may play a role in the development of osteoarthritis (OA), and vitamin D receptor (VDR) polymorphisms have been associated with several common diseases including OA by some studies. The aim of this study was to explore whether the VDR polymorphisms confer susceptibility to OA.

METHODS

We conducted meta-analyses on the associations between the VDR TaqI, BsmI, ApaI polymorphisms and OA using: (1) allele contrast, (2) the recessive model, (3) the dominant model, and (4) contrast of homozygotes, using fixed and random effects models.

RESULTS

A total of 10 relevant studies on VDR polymorphisms and OA were included in this meta-analysis, which involved in total 1591 OA patients and 1781 controls. Nine studies were performed on VDR TaqI polymorphisms, 6 on VDR BsmI polymorphisms, 5 on VDR ApaI polymorphisms. Accordingly, to our meta-analysis of VDR TaqI polymorphisms, no association was found between OA and the VDR TaqI T allele among in all study subjects (OR=0.841, 95% CI=0.663-1.067, p=0.155). Stratification by ethnicity yielded no association between the VDR TaqI T allele and OA in Europeans or Asians. Moreover, no association was found between OA and the VDR TaqI polymorphisms by the meta-analyses of recessive and dominant models, and contrast of homozygotes. No association was found between OA and the VDR polymorphisms with respect to the BsmI and ApaI polymorphisms by meta-analyses.

CONCLUSIONS

No association was found between the VDR TaqI, BsmI, or ApaI polymorphisms and OA susceptibility by this meta-analysis, which included 3372 subjects.

Association of KLOTHO gene polymorphisms with knee osteoarthritis in Greek population

Based on the fact that klotho-deficient mice exhibit multiple aging phenotypes, including osteopenia and subchondral sclerosis of joints and on the recent observation that KLOTHO gene plays an important role in calcium/phosphate homeostasis, we explored the possibility whether human KLOTHO gene polymorphisms are associated with osteoarthritis (OA). A total of 752 individuals participated in the study. The knee OA group consisted of 369 patients; 298 women (mean age 65.9 +/- 8.2; range 40-92 years) and 71 men (mean age 65.7 +/- 9.1; range 30-82 years). The control population consisted of 383 subjects; 231 women (mean age 65.8 +/- 8.4; range 35-90 years) and 152 men (mean age 61.5 +/- 9.3; range 28-87 years). Four SNPs--G395A in the promoter region, G1110C in exon 2, C1818T and C2298T in exon 4--were genotyped. A significant genotypic and allelic association was observed in SNP C2998T and knee OA, while genotype GA of SNP G395A was significantly associated (p = 0.039) with knee OA in females only. For the first time, an association was observed between SNPs G395A and C2998T of the KLOTHO gene and knee osteoarthritis implicating KLOTHO in OA pathogenesis.

Cellular roles of ADAM12 in health and disease

ADAM12 belongs to the large family of ADAMs (a disintegrin and metalloproteases) and possesses extracellular metalloprotease and cell-binding functions, as well as intracellular signaling capacities. Interest in ADAM12 has increased recently because its expression is related to tumor progression and it is a potential biomarker for breast cancer. It is therefore important to understand ADAM12's functions. Many cellular roles for ADAM12 have been suggested. It is an active metalloprotease, and has been implicated in insulin-like growth factor (IGF) receptor signaling, through cleavage of IGF-binding proteins, and in epidermal growth factor receptor (EGFR) pathways, via ectodomain shedding of membrane-tethered EGFR ligands. These proteolytic events may regulate diverse cellular responses, such as altered cell differentiation, proliferation, migration, and invasion. ADAM12 may also regulate cell-cell and cell-extracellular matrix contacts through interactions with cell surface receptors - integrins and syndecans - potentially influencing the actin cytoskeleton. Moreover, ADAM12 interacts with several cytoplasmic signaling and adaptor molecules through its intracellular domain, thereby directly transmitting signals to or from the cell interior. These ADAM12-mediated cellular effects appear to be critical events in both biological and pathological processes. This review presents current knowledge on ADAM12 functions gained from in vitro and in vivo observations, describes ADAM12's role in both normal physiology and pathology, particularly in cancer, and discusses important areas for future investigation.

Potential influence of IL1B haplotype and IL1A-IL1B-IL1RN extended haplotype on hand osteoarthritis risk

OBJECTIVE

To assess osteoarthritis (OA) association with the human interleukin-1 (IL-1) region.

DESIGN

Sixty-four European-descent cases with radiographic hand OA and 48 European-descent controls were genotyped at nine single nucleotide polymorphism (SNP), one variable-number-of-tandem-repeat (VNTR), and one microsatellite marker extending across loci for IL-1alpha (IL1A), IL-1beta (IL1B), and IL-1 receptor antagonist (IL1RN). The genotype data were used to reconstruct individual locus haplotypes, and then locus haplotypes were used as superalleles for extended haplotype reconstruction.

RESULTS

Nine different extended IL1A-IL1B-IL1RN haplotypes occurred at a frequency 0.05 or greater in either cases or controls. Only two IL1A-IL1B-IL1RN extended haplotypes were consistent with previously described extended risk haplotypes and totaled n=9 in cases and n=3 in controls [odds ratio (OR) 2.1, Haldane's chi(2) 1.67, one-sided P 0.1]. Our prior report showed hand OA association with homozygous IL1B rs1143633 minor allele genotype. All except one extended risk haplotype copy also had the IL1B rs1143633 minor allele. The rs1143633 genotype association was explained by one common six-SNP IL1B haplotype bearing rs1143633 minor allele and also risk alleles at rs1143634, rs1143627, and rs16944, component markers of the previously described extended risk haplotypes. The IL1B haplotype bearing all three risk alleles was found in 16 haplotype-homozygous hand OA cases and in four haplotype-homozygous controls and conferred OR 3.4 among homozygotes (nominal P value 0.006).

CONCLUSION

Our evidence broadly supports the genetic association of OA phenotypes with an IL-1 region extended risk haplotype and specifically IL1B genotype. The extended risk haplotype previously associated with hip OA appears to be less frequent and has weaker genetic effect in hand OA. Hand OA risk is conferred by homozygous state for the IL1B haplotype characteristic of the extended risk haplotype.

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.

Vitamin D receptor gene polymorphisms and susceptibility of hand osteoarthritis in Finnish women

We examined whether polymorphisms of the vitamin D receptor (VDR) gene was associated with individual risk of hand osteoarthritis (OA). Radiographs of both hands of 295 dentists and of 248 teachers were examined and classified for the presence of OA using reference images. The VDR ApaI and TaqI genotypes were determined by PCR-based methods. No association was observed between the VDR polymorphisms and the odds of overall hand OA. However, the carriers of the VDR t allele or At haplotype were at almost half the odds of symmetrical hand OA (odds ratio [OR] = 0.60, 95% confidence interval [CI] = 0.38–0.94 and OR = 0.59, 95% CI = 0.38–0.93, respectively) compared with the carriers of the T allele and of the non-At haplotype, respectively. Increased odds of this disease, on the contrary, was observed for women with two copies of the VDR a allele (OR = 1.93, 95% CI = 1.99–3.70) compared with women with the AA genotype. Conversely, the VDR a allele carriage was associated with a tendency of lowered odds of osteophyte (OR = 0.51, 95% CI = 0.25–1.03). When the genotype data were used to construct haplotypes, the VDR AaTt joint genotype appeared to pose a remarkably lower odds (OR = 0.26, 95% CI = 0.08–0.91) of osteophyte compared with the AAtt joint genotype. As a novel finding we observed a joint effect of a low calcium intake and VDR polymorphisms on symmetrical OA; the OR was 2.64 (95% CI = 1.29–5.40) for carriers of the aT haplotype with low daily calcium intake compared with non-carriers of the haplotype with high daily calcium intake. Our results suggest that VDR gene polymorphisms play a role in the etiology of symmetrical hand OA. Moreover, the association between the VDR gene and OA may be modified by calcium intake.

Absence of linkage to chromosomes 6q and 16p in a Greek population with knee osteoarthritis

Osteoarthritis (OA) is a common age-related debilitating disease of the joints characterized by degeneration of the articular cartilage which leads to joint pain, discomfort, and immobility. Several risk factors have been associated with OA including a genetic predisposition. Specific chromosomal regions have thus far been associated with susceptibility to OA, the strongest being on chromosomes 2, 6, and 16. We hereby report our data on 34 Central Greek knee OA families that were investigated for linkage to the chromosome 6q and 16p susceptibility regions. All affected members had undergone total knee replacement surgery (TKR) at a single large Orthopedics Unit in Central Greece. Nineteen microsatellite markers were selected, 15 for chromosome 6q and 4 for chromosome 16p at a distance of approximately 7 cm. Allele fragment sizes were determined by an automated DNA sequencer using the Fragment Analysis Software. Our results revealed a statistically significant difference in the ratio of affected females to males with knee OA and also showed that there is no evidence of linkage to regions 6q and 16p in a cohort of Central Greek pedigrees with knee OA.

Osteoarthritis susceptibility loci defined by genome scan meta-analysis

Genome scans for osteoarthritis (OA) have yielded inconsistent results. The absence of replication of linkage might be due to lack of power of individual studies. A meta-analysis of the published data was performed to assess evidence for linkage of OA across genome scan studies. Three OA whole-genome scans including 893 families with 3,000 affected individuals were used for genome scan meta-analysis (GSMA). A total of 5 bins lie above 95% confidence level (P = 0.05) and 1 bin is above 99% confidence level (P = 0.01) in OA GSMA; bins 7.6 (7q34-7q36.3, Psumrnk = 0.0035), 11.3 (11p12-11q13.4), 6.3 (6p21.1-6q15), 2.8 (2q31.1-2q34) and 15.3 (15q21.3-15q26.1). The highest summed rank was observed at bin 7.6. In conclusion, the OA GSMA has shown chromosome 7q34-7q36.3 with the highest summed rank and four additional loci with significant summed ranks across studies.

Osteoarthritis susceptibility loci defined by genome scan meta-analysis

Genome scans for osteoarthritis (OA) have yielded inconsistent results. The absence of replication of linkage might be due to the lack of power of individual studies. A meta-analysis of published data was performed to assess evidence for linkage of OA across genome scan studies. Three OA whole-genome scans including 893 families with 3,000 affected individuals were used for genome scan meta-analysis (GSMA). A total of five bins lie above 95% confidence level (P=0.05) and one bin is above 99% confidence level (P=0.01) in OA GSMA; bins 7.6 (7q34-7q36.3, P (sumrnk) =0.0035), 11.3 (11p12-11q13.4), 6.3 (6p21.1-6q15), 2.8 (2q31.1-2q34) and 15.3 (15q21.3-15q26.1). The highest summed bin was bins 7.6. In conclusion, the OA GSMA has shown that chromosome 7q34-7q36.3 have the highest summed rank and four additional loci with significant summed ranks across studies.

Reproducible genetic associations between candidate genes and clinical knee osteoarthritis in men and women

OBJECTIVE

Osteoarthritis (OA) is recognized to have a genetic component, and in this study, we aimed to replicate in a case-control study of men and women with clinical knee OA genetic associations in 12 candidate genes previously reported to be associated with OA.

METHODS

Twenty-five single-nucleotide polymorphisms were genotyped in 298 men and 305 women ages 50-86 who were diagnosed as having knee OA, as assessed both clinically and radiographically, and in 297 men and 299 women matched for age and ethnicity (controls). Standardized anteroposterior radiographs of the knee in extension were performed on each of the cases, and all cases met the American College of Rheumatology criteria for OA of the knee. Genotype and haplotype frequencies in cases and controls were compared separately in men and women. The 12 genes tested were AACT, ADAM12, BMP2, CD36, CILP, COX2, ESR1, NCOR2, OPG, TNA, TNFAIP6, and VDR.

RESULTS

Eight of the candidate genes were associated in women and 5 in men, and only 3 genes (TNFAIP6, NCOR2, and CD36) were not significantly associated in either sex. The strongest associations in terms of odds ratios (ORs) were a haplotype in ADAM12 (OR 7.1 [95% confidence interval (95% CI) 3.3-33.8]) and a haplotype in ESR1 (OR 3.6 [95% CI 1.18-10.98]) in women. The same ADAM12 haplotype (OR 2.54 [95% CI 1.2-5.4]) and a haplotype in the CILP gene (OR 0.38 [95% CI 0.23-0.62]) were the strongest associations in men.

CONCLUSION

We found that genes previously identified by their association with subclinical features of knee OA or progression were also associated with clinical knee OA. These genetic associations may identify individuals at a particularly high risk of developing knee OA.

Sex and ethnic differences in the association ofASPN,CALM1,COL2A1,COMP, andFRZB with genetic susceptibility to osteoarthritis of the knee

OBJECTIVE

To assess whether the association of genetic polymorphisms with osteoarthritis (OA) in other populations could be replicated in a large, multicenter, mixed-sex, case-control study of clinical knee OA.

METHODS

Genetic polymorphisms in OA candidate genes were genotyped in 298 men and 305 women, ages 50-86 years, all of whom had a diagnosis of knee OA as assessed clinically and radiographically, and in 300 male and 299 female control subjects matched for age and ethnicity. Allele and haplotype frequencies for 5 genes (ASPN, CALM1, COL2A1, COMP, and FRZB) previously tested for association with hip and/or knee OA in other populations were compared between patients and control subjects, analyzing men and women separately.

RESULTS

The same FRZB 2-marker single-nucleotide polymorphism (SNP) haplotype associated with hip OA in other populations of Caucasian women was shown to increase the risk of knee OA among the women (but not the men) in the current study (odds ratio [OR] 2.87, P < 0.04). The CALM1 SNP, which affects the risk of hip OA in Japanese individuals, was not shown to be associated with susceptibility to OA in men or women. COL2A1 haplotypes were demonstrated to be associated with a decreased risk of knee OA in men (OR 0.68, P < 0.005) but not in women. COMP haplotypes that were associated with susceptibility to knee OA were different in men and women (P < 0.014 and P < 0.032, respectively). A meta-analysis of these data and those from previously published reports indicated a strong association between the FRZB G324 allele (P < 0.0003) and suggested that an ASPN allele is protective against the risk of knee OA in Caucasians (P < 0.02).

CONCLUSION

Our results indicate that genetic polymorphisms affecting knee OA vary between populations (Japanese versus Caucasian) and sexes and indicate a role for ASPN, COMP, FRZB, and COL2A1 in Caucasians.

Recent advances in the genetic investigation of osteoarthritis

Osteoarthritis (OA) demonstrates considerable clinical heterogeneity, generating heated debate over whether OA is a single disease or a complex mix of disparate diseases and concerning which tissues are principally involved in disease initiation and progression. Epidemiological studies have demonstrated a major genetic component to OA risk. However, these studies have also revealed differences in risk between males and females and for disease at different skeletal sites. This observation has resulted in the concept of genes for specific sites rather than a generalised OA phenotype. Recent breakthroughs have shed considerable light on the nature of OA genetic susceptibility. Many candidate genes have been confirmed, such as the interleukin-1 gene cluster and the oestrogen alpha-receptor gene ESR1. Genome-wide linkage scans have revealed several regions harbouring novel loci, some of which are beginning to yield their genes.

Genetic background increases the risk of hip osteoarthritis

Using a cohort of 49 families with at least one affected female sibling pair who had total hip arthroplasty for end-stage primary osteoarthritis, we determined the prevalence and relative risk of symptomatic and radiographic osteoarthritis in 145 children. The relative risk of symptomatic radiographic osteoarthritis in these 145 offspring was 3.5 times greater than in 119 age-matched controls (95% confidence interval; range, 2.0-6.2). Most symptoms and radiographic changes involved the hip. Results of this study showed vertical transmission of primary osteoarthritis and that genetic influences play a major role in osteoarthritis of the hip in the Caucasian population.

Activation of the discoidin domain receptor 2 induces expression of matrix metalloproteinase 13 associated with osteoarthritis in mice

Human genetic studies indicate that mutations in type IX and XI collagens result in early-onset osteoarthritis (OA) with a wide spectrum of osteochondrodysplasia. However, a convincing causal chain of events underlying the role of these collagen mutations in the pathogenesis of OA has not been elucidated. Here we show that the expression of a cell surface collagen receptor, discoidin domain receptor 2 (DDR2), is increased in chondrocytes of the articular cartilage of knee joints in mice that develop OA as a result of a heterozygous mutation in type XI collagen. At the same time point, 6 months, we also found increased expression and activity of matrix metalloproteinase 13 (MMP-13) in the mutant mouse knee cartilage. The expression of both DDR2 and MMP-13 was increased in chondrocytes cultured on plates coated with native type II collagen but not on gelatin, and overexpression of DDR2, but not of a truncated form, was found to induce the expression of MMP-13 when chondrocytes were cultured on type II collagen but not on plastic. The DDR2-induced expression of MMP-13 appears to be specific, since we did not observe induction of MMP-1, MMP-3, MMP-8, ADAMTS-4, ADAMTS-5, and IL-1 transcripts in human chondrocytes or Mmp-3, Mmp-8, Adamts-4, Adamts-5, and Il-1 in mouse chondrocytes. Our data suggest that the defect in the cartilage matrix of mice that are heterozygous for a type XI collagen mutation (cho/+) permits activation and up-regulation of DDR2 in chondrocytes. This could be due to increased exposure of chondrocytes to type II collagen as a result of the decreased amount of type XI collagen in the mutant cartilage. The specific induction of MMP-13 by DDR2 in response to its cartilage-specific ligand, type II collagen, may contribute to cartilage damage in hereditary OA.

Familial inheritance of osteoarthritis: documented family subsets

Identifying susceptibility genes for a common complex disease is complicated by heterogeneity at several levels including allelic, locus, clinical, and population. The latter two can be alleviated by focusing on particular subsets of families that have well-defined disease. For osteoarthritis it was commonly thought that a generalized disease approach was the wisest ascertainment because this would target a systemic disease that had to have a major genetic component. However, this intuitive idea has not yet provided the breakthroughs many expected and it has become apparent that a joint-specific and gender-specific approach may be more fruitful. Large collections of osteoarthritis cohorts have been assembled either as part of prospective studies or more directly. Some of these collections have targeted specific joints, others have not. The latter are, however, amenable to stratification. Many collectors included the acquisition of DNA as a core study aim. A variety of osteoarthritis subsets are therefore available for genetic analysis. Open accessibility is another matter. Although many collections were funded partly or wholly by public or charitable organizations, they can be jealously guarded or have arcane access rights. Open access, with necessary safeguards, is something the osteoarthritis research community should strive for if progress toward susceptibility gene identification is to be swift.

Functional variants within the secreted frizzled-related protein 3 gene are associated with hip osteoarthritis in females

Osteoarthritis (OA) is a leading cause of disability in Western society with multiple risk factors, including a complex genetic pattern. Identifying loci involved in the heredity of OA might lead to insights into the molecular pathogenesis of this common disorder. A previous genome scan mapped a primary hip OA susceptibility locus to chromosome 2q with a maximum multipoint logarithm of odds score of 1.6 in 378 affected sibling pair families. Here, microsatellite targeting of eight candidate genes in this region from 2q23-2q32 demonstrated significant associations with the tumor necrosis factor alpha-induced protein 6 gene in all probands and the integrin alpha 6 and frizzled motif associated with bone development (FRZB) genes in female probands. However, genotyping showed lack of association for a nonsynonymous single-nucleotide polymorphism in tumor necrosis factor alpha-induced protein 6, whereas a single-nucleotide polymorphism in FRZB resulting in an Arg324Gly substitution at the carboxyl terminus was associated with hip OA in the female probands (P = 0.04). This association was confirmed in an independent cohort of female hip cases (n = 338; P = 0.04). In addition, a haplotype coding for substitutions of two highly conserved arginine residues (Arg200Trp and Arg324Gly) in FRZB was a strong risk factor for primary hip OA, with an odds ratio of 4.1 (P = 0.004). FRZB encodes secreted frizzled-related protein 3, which is a soluble antagonist of wingless (wnt) signaling. Variant secreted frizzled-related protein 3 with the Arg324Gly substitution had diminished ability to antagonize wnt signaling in vitro. Hence, functional polymorphisms within FRZB confer susceptibility for hip OA in females and implicate the wnt signaling pathway in the pathogenesis of this disease.

Association study of candidate genes for the prevalence and progression of knee osteoarthritis

OBJECTIVE

Osteoarthritis (OA), characterized by late-onset degeneration of articular cartilage, is recognized to have a genetic component. We examined the role of 26 single-nucleotide polymorphisms (SNPs) from 24 candidate genes in OA susceptibility and progression.

METHODS

We compared human complementary DNA libraries from OA-affected and normal cartilage and synovium and selected 22 genes in addition to the estrogen receptor alpha and vitamin D receptor genes. Based on the availability of polymorphisms, we proceeded to test whether genetic variation at those genes affected susceptibility to or progression of radiographic knee OA over a 10-year period in 749 women (mean age 64 years) from the longitudinal Chingford Study.

RESULTS

After adjusting for age and body mass index, we observed significant associations at ADAM12, BMP2, CD36, COX2, and NCOR2 with 3 OA susceptibility traits (presence/absence of joint space narrowing [JSN], presence/absence of osteophytes, and Kellgren/Lawrence [K/L] score). For the OA progression traits (change over 10 years in the K/L score, osteophyte grade, and JSN grade), we found significant associations with ADAM12, CILP, OPG, and TNA. Overall, we observed 15 associations with nominal significance (P < 0.05) and, by permutation analysis, found that such a number would be observed by chance only 3.8% of the time. Although these tests require replication, the stronger genetic associations observed are unlikely to be attributable simply to multiple comparisons.

CONCLUSION

Our results suggest that OA severity and progression have a multigenic and feature-specific nature. These findings should encourage the development of genetic diagnostics for OA progression based on multiple SNPs and help unravel some of the complex disease mechanisms in OA.

Osteoarthritis

Osteoarthritis is a chronic degenerative disorder characterised by cartilage loss. It is extremely prevalent in society and is a major cause of disability. It is important to treat osteoarthritis effectively using a multidisciplinary approach tailored to the patient's needs. This paper reviews current thinking on the aetiology, pathogenesis, investigations, and management of osteoarthritis. The paper also discusses the challenges for developing good quality outcome measures for use in large scale multicentre clinical trials for new osteoarthritis treatments, especially disease modifying osteoarthritis drugs.

Genetic epidemiology: disease susceptibility and severity

Genetic factors are increasingly recognized to have an important contribution to the occurrence of both inflammatory and noninflammatory rheumatic disease. Although identifying the specific genetic mechanisms involved in the rheumatic diseases continues to present considerable challenges, the prospect of identifying individual gene action has been brought closer by a number of recent developments. These include newer approaches to phenotype definition, refinements in statistical tools for analysis, and the advent of newer technologies, including the use of microarrays. In this article, we review some of these developments together with the recent literature on the contribution of both broad and specific genetic factors to the spectrum of rheumatic disease. We also consider contemporary opinions on the potential impact of genetic discoveries to human health.