Background and objective

Until recently, there has been little agreement between conflicting results of osteoarthritis (OA) linkage. The purpose of this study was to conduct a whole‐genome linkage scan to identify susceptibility loci for idiopathic hand OA in a large, population‐based sample of females.

Methods

Two OA‐related radiographic phenotypes DIP (distal interphalangeal joints)‐OA and Tot‐KL (Kellgren‐Lawrence score for both hands) chosen a priori were examined on 538 (269 pairs) monozygous and 1256 (628 pairs) dizygous (DZ) females. A genome‐wide scan using microsatellite markers spaced 10 cM apart was performed on 1028 DZ twins. First, the heritability of the two OA phenotypes was estimated. Next, multipoint linkage analysis was conducted using a modified version of the Haseman–Elston method in a generalised linear model.

Results

Heritability for DIP‐OA and Tot‐KL was found to be 47.6% and 67.4%, respectively. A genome‐wide scan produced reliable evidence of significant linkage of DIP‐OA on chromosome 2 at 90 cM (logarithmic odds ratio (LOD) = 2.90) and for Tot‐KL on chromosome 19 at 65 cM (LOD = 4.26). These results are in agreement with data published previously. Several other significant linkage peaks were observed—for example, on chromosome 1 at 250 cM and on chromosome 3 at 30 cM—but were confirmed less reliably.

Conclusion

This is one of the largest OA linkage studies performed to date and provides clear evidence for linkage at two quantitative trait loci (on chromosome 2 at 90 cM and on chromosome 19 at 65 cM). As the results were robust and replicated in previous smaller studies, the fine mapping of these regions is a logical next step to pinpoint potential susceptibility gene(s) of interest.

Objective

To address the need for standardization of osteoarthritis (OA) phenotypes by examining the effect of heterogeneity among symptomatic (SOA) and radiographic osteoarthritis (ROA) phenotypes.

Methods

Descriptions of OA phenotypes of the 28 studies involved in the TREAT-OA consortium were collected. To investigate whether different OA definitions result in different association results, we created hip OA definitions used within the consortium in the Rotterdam Study-I and tested the association of hip OA with gender, age and BMI using one-way ANOVA. For radiographic OA, we standardized the hip, knee and hand ROA definitions and calculated prevalence's of ROA before and after standardization in 9 cohort studies. This procedure could only be performed in cohort studies and standardization of SOA definitions was not feasible at this moment.

Results

In this consortium, all studies with symptomatic OA phenotypes (knee, hip and hand) used a different definition and/or assessment of OA status. For knee, hip and hand radiographic OA 5, 4 and 7 different definitions were used, respectively. Different hip OA definitions do lead to different association results. For example, we showed in the Rotterdam Study-I that hip OA defined as “at least definite JSN and one definite osteophyte” was not associated with gender (p=0.22), but defined as “at least one definite osteophyte” was significantly associated with gender (p=3×10−9). Therefore, a standardization process was undertaken for radiographic OA definitions. Before standardization a wide range of ROA prevalence's was observed in the 9 cohorts studied. After standardization the range in prevalence of knee and hip ROA was small. Standardization of SOA phenotypes was not possible due to the case-control design of the studies.

Conclusion

Phenotype definitions influence the prevalence of OA and association with clinical variables. ROA phenotypes within the TREAT-OA consortium were standardized to reduce heterogeneity and improve power in future genetics studies.

Our aim was to examine the association between serum dehydroepiandrosterone sulfate (DHEAS) at baseline and BMD change at the femoral neck (FN) and lumbar spine (LS) in postmenopausal women during a 15-year follow-up. All participants were from the Chingford Study. BMD at the FN and LS were measured eight times during the 15-year follow-up by dual-energy X-ray absorptiometry. DHEAS at baseline was measured using radioimmunoassay. Data on height, weight, and hormone-replacement therapy (HRT) status were obtained at each visit. Multilevel linear regression modeling was used to examine the association between longitudinal BMD change at the FN and LS and DHEAS at baseline. Postmenopausal women (n = 1,003) aged 45–68 years (mean 54.7) at baseline were included in the study. After adjustment for baseline age, estradiol, HRT, and BMI, BMD at the FN decreased on average 0.49% (95% CI 0.31–0.71%) per year; and the decline was slowed down by 0.028% per squared year. Increase of DHEAS (each micromole per liter) was associated with 0.49% less bone loss at the FN (95% CI 0.21–0.71%, P = 0.001). However, this strong association became slightly weaker over time. Similar but weaker results were obtained for LS BMD. Our data suggest that high serum DHEAS at baseline is associated with less bone loss at both FN and LS and this association diminishes over time. The nature of the association is unclear, but such an association implies that, in managing BMD loss, women might benefit from maintaining a high level of DHEAS.

Adiponectin is an insulin sensitizer in muscle and liver and low serum levels characterise obesity and insulin resistance. Eight tagging SNPs in the ADIPOQ gene and promoter were selected and association with serum adiponectin was tested in two independent samples of Caucasian females: the Chingford Study (n=808, mean age 62.8±5.9 years) and Twins UK (n=2718, mean age 47.4±12.6 years). In the Chingford cohort, −11391 G/A, −10066 G/A (rs182052), −7734 C/A (rs16861209), +276 G/T (rs1501299) and +3228 C/T (rs1063537) were significantly associated with fasting serum adiponectin (Ps=1.00 × 10−4 to 1.40 × 10−2). Associations with all except +3228 C/T were replicated in the Twins UK cohort (Ps=3.19 × 10−9 to 6.00 × 10−3). In Chingford subjects, the twelve most common 8-SNP haplotypes (freq. 1.90%) explained 2.85% (p=5.00 × 10−2) and in Twins UK subjects, the four most common 5-SNP haplotypes (freq. >5.00%) explained 1.66% of the variance (p=5.83 × 10−7). To investigate effects of −11391 G/A (rs17300539) and −11377 C/G (rs266729) on promoter activity, 1.2 kb of the ADIPOQ promoter region was cloned in a luciferase reporter plasmid and the four haplotypes were transfected in differentiated 3T3-L1 adipocytes. No significant allelic effects on promoter activity were found.

Objective

There is a great need for identification of biomarkers that could improve the prediction of early osteoarthritis (OA). We undertook this study to determine whether circulating levels of interleukin-6 (IL-6), tumor necrosis factor α (TNFα), and C-reactive protein (CRP) can serve as useful markers of radiographic knee OA (RKOA) in a normal human population.

Methods

RKOA data were obtained from the cohort of the Chingford Study, a prospective population-based study of healthy, middle-aged British women. The RKOA-affected status of the subjects was assessed using the Kellgren/Lawrence (K/L) grade as determined on radiographs obtained at baseline (n = 908) and at 10 years and 15 years thereafter. Serum levels of CRP, IL-6, and TNFα were assayed at 5, 8, and 15 years, using high-sensitivity commercial assays. A K/L grade of ≥2 in either knee was used as the outcome measure. Statistical analyses included analysis of variance for repeated measurements and logistic regression models, together with longitudinal modeling of dichotomous responses.

Results

During 15 years of followup, the prevalence of RKOA (K/L grade ≥2) increased from 14.7% to 48.7% (P < 0.00001 versus baseline). The body mass index (BMI) and circulating levels of CRP and IL-6 were consistently and significantly higher in subjects diagnosed as having RKOA. When multiple logistic regression was applied to the data, the variables of older age (P = 3.93 × 10−5), higher BMI at baseline (P = 0.0003), and increased levels of IL-6 at year 5 (P = 0.0129) were determined to be independent predictors of the appearance of RKOA at year 10. The results were fully confirmed using longitudinal modeling of repeated measurements of the data obtained at 3 visits. The odds ratio for RKOA in subjects whose IL-6 levels were in the fourth quartile of increasing levels (versus the first quartile) was 2.74 (95% confidence interval 1.94–3.87).

Conclusion

This followup study showed that individuals were more likely to be diagnosed as having RKOA if they had a higher BMI and increased circulating levels of IL-6. These results should stimulate more work on IL-6 as a potential therapeutic target.

Objective

To assess if a coding variant in the gene encoding transient receptor potential cation channel, subfamily V, member 1 (TRPV1) is associated with genetic risk of painful knee osteoarthritis (OA).

Methods

The Ile585Val TRPV1 variant encoded by rs8065080 was genotyped in 3270 cases of symptomatic knee OA, 1098 cases of asymptomatic knee OA and 3852 controls from seven cohorts from the UK, the USA and Australia. The genetic association between the low-pain genotype Ile–Ile and risk of symptomatic and asymptomatic knee OA was assessed.

Results

The TRPV1 585 Ile–Ile genotype, reported to be associated with lower thermal pain sensitivity, was associated with a lower risk of symptomatic knee OA in a comparison of symptomatic cases with healthy controls, with an odds ratio (OR) of 0.75 (95% CI 0.64 to 0.88; p=0.00039 by meta-analysis) after adjustment for age, sex and body mass index. No difference was seen between asymptomatic OA cases and controls (OR=1.02, 95% CI 0.82 to 1.27 p=0.86) but the Ile–Ile genotype was associated with lower risk of symptomatic versus asymptomatic knee OA adjusting for covariates and radiographic severity (OR=0.73, 95% CI 0.57 to 0.94 p=0.0136). TRPV1 expression in articular cartilage was increased by inflammatory cytokines (tumour necrosis factor α and interleukin 1). However, there were no differences in TRPV1 expression in healthy and arthritic synovial tissue.

Conclusions

A genotype involved in lower peripheral pain sensitivity is significantly associated with a decreased risk of painful knee OA. This indicates a role for the pro-nociceptive gene TRPV1 in genetic susceptibility to symptomatic knee OA, which may also be influenced by a role for this molecule in cartilage function.

Objective

Subtle deformities of the hip joint are implicated in the etiology of osteoarthritis (OA) of the hip. Parameters that quantify these deformities may aid understanding of these associations. We undertook this study to examine relationships between such parameters and the 19-year risk of total hip arthroplasty (THA) for end-stage OA.

Methods

A new software program designed for measuring morphologic parameters around the hip was developed and validated in a reliability study. THA was the outcome measure for end-stage OA. A nested case–control study was used with individuals from a cohort of 1,003 women who were recruited at year 1 in 1989 and followed up to year 20 (the Chingford Study). All hips with THA by year 20 and 243 randomly selected control hips were studied. Pelvis radiographs obtained at year 2 were analyzed for variations in hip morphology. Measurements were compared between the THA case group and the control group.

Results

Patients with THA had a higher prevalence of cam deformity than did their respective controls (median alpha angle 62.4° versus 45.8° [P = 0.001]; mean modified triangular index height 28.5 mm versus 26.9 mm [P = 0.001]) as well as a higher prevalence of acetabular dysplasia (mean lateral center edge angle 29.5° versus 34.3° [P = 0.001]; median extrusion index 0.25 versus 0.185 [P = 0.009]). Logistic regression analyses clustering by subject and adjusting for radiographic hip OA at year 2 showed that these morphologic parameters were still significantly associated with THA by year 20. The alpha angle and lateral center edge angle predicted the risk of THA independently when included in the same model.

Conclusion

This investigation describes measurements that predict the risk of THA for end-stage OA by year 20, independently of the presence of radiographic hip OA at year 2. These measurements can be made on an anteroposterior pelvis radiograph, which is an inexpensive and commonly used clinical method of investigation.

To identify genes involved in osteoarthritis (OA), the most prevalent form of joint disease, we performed a genome-wide association study (GWAS) in which we tested 500,510 Single Nucelotide Polymorphisms (SNPs) in 1341 OA cases and 3496 Dutch Caucasian controls. SNPs associated with at least two OA-phenotypes were analysed in 14,938 OA cases and approximately 39,000 controls. The C-allele of rs3815148 on chromosome 7q22 (MAF 23%, 172 kb upstream of the GPR22 gene) was consistently associated with a 1.14-fold increased risk (95%CI: 1.09–1.19) for knee- and/or hand-OA (p=8×10−8), and also with a 30% increased risk for knee-OA progression (95%CI: 1.03–1.64, p=0.03). This SNP is in almost complete linkage disequilibrium with rs3757713 (located 68 kb upstream of GPR22) which is associated with GPR22 expression levels in lymphoblast cell lines (p=4×10−12). GPR22 encodes an G-protein coupled receptor with unkown ligand (orphan receptor). Immunohistochemistry experiments showed absence of GPR22 in normal mouse articular cartilage or synovium. However, GPR22 positive chondrocytes were found in the upper layers of the articular cartilage of mouse knee joints that were challenged by in vivo papain treatment or in the presence of interleukin-1 driven inflammation. GRP22 positive chondrocyte-like cells were also found in osteophytes in instability-induced OA. In addition, GPR22 is also present in areas of the brain involved in locomotor function. Our findings reveal a novel common variant on chromosome 7q22 to influence susceptibility for prevalence and progression of OA.

Osteoarthritis (OA) is the most common form of arthritis and a major cause of disability. This study evaluates the association in Caucasian populations of two single nucleotide polymorphisms (SNPs) mapping to the Human Leukocyte Antigen (HLA) region and deriving from a genome wide association scan (GWAS) of knee OA in Japanese populations. The frequencies for rs10947262 were compared in 36,408 controls and 5,749 knee OA cases from European-descent populations. rs7775228 was tested in 32,823 controls and 1,837 knee OA cases of European descent. The risk (major) allele at rs10947262 in Caucasian samples was not significantly associated with an odds ratio (OR)  = 1.07 (95%CI 0.94 -1.21; p = 0.28). For rs7775228 the meta-analysis resulted in OR = 0.94 (95%CI 0.81-1.09; p = 0.42) for the allele associated with risk in the Japanese GWAS. In Japanese individuals these two SNPs are in strong linkage disequilibrium (LD) (r2 = 0.86) with the HLA class II haplotype DRB1*1502 DQA1*0103 DQB1*0601 (frequency 8%). In Caucasian and Chinese samples, using imputed data, these SNPs appear not to be in LD with that haplotype (r2<0.07). The rs10947262 and rs7775228 variants are not associated with risk of knee OA in European descent populations and they do not appear tag the same HLA class II haplotype as they do in Japanese individuals.

Recent genome-wide (GW) scans have identified several independent loci affecting human stature, but their contribution through the different skeletal components of height is still poorly understood. We carried out a genome-wide scan in 12,611 participants, followed by replication in an additional 7,187 individuals, and identified 17 genomic regions with GW-significant association with height. Of these, two are entirely novel (rs11809207 in CATSPER4, combined P-value = 6.1×10−8 and rs910316 in TMED10, P-value = 1.4×10−7) and two had previously been described with weak statistical support (rs10472828 in NPR3, P-value = 3×10−7 and rs849141 in JAZF1, P-value = 3.2×10−11). One locus (rs1182188 at GNA12) identifies the first height eQTL. We also assessed the contribution of height loci to the upper- (trunk) and lower-body (hip axis and femur) skeletal components of height. We find evidence for several loci associated with trunk length (including rs6570507 in GPR126, P-value = 4×10−5 and rs6817306 in LCORL, P-value = 4×10−4), hip axis length (including rs6830062 at LCORL, P-value = 4.8×10−4 and rs4911494 at UQCC, P-value = 1.9×10−4), and femur length (including rs710841 at PRKG2, P-value = 2.4×10−5 and rs10946808 at HIST1H1D, P-value = 6.4×10−6). Finally, we used conditional analyses to explore a possible differential contribution of the height loci to these different skeletal size measurements. In addition to validating four novel loci controlling adult stature, our study represents the first effort to assess the contribution of genetic loci to three skeletal components of height. Further statistical tests in larger numbers of individuals will be required to verify if the height loci affect height preferentially through these subcomponents of height.

Author Summary

The first genetic association studies of adult height have confirmed a role of many common variants in influencing human height, but to date, the genetic basis of differences between different skeletal components of height have not been addressed. Here, we take advantage of recent technical and methodological advances to examine the role of common genetic variants on both height and skeletal components of height. By examining nearly 20,000 individuals from the UK and the Netherlands, we provide statistically significant evidence that 17 genomic regions are associated with height, including four novel regions. We also examine, for the first time, the association of these 17 regions with skeletal size measurements of spine, femur, and hip axis length, a measurement of hip geometry known to influence the risk of osteoporotic fractures. We find that some height loci are also associated with these skeletal components, although further statistical tests will be required to verify if these genetic variants act differentially on the individual skeletal measurements. The knowledge generated by this and other studies will not only inform the genetics of human quantitative variation, but will also lead to the potential discovery of many medically important polymorphisms.