Novel Genetic Variants for Cartilage Thickness and Hip Osteoarthritis.

Osteoarthritis is one of the most frequent and disabling diseases of the elderly. Only few genetic variants have been identified for osteoarthritis, which is partly due to large phenotype heterogeneity. To reduce heterogeneity, we here examined cartilage thickness, one of the structural components of joint health. We conducted a genome-wide association study of minimal joint space width (mJSW), a proxy for cartilage thickness, in a discovery set of 13,013 participants from five different cohorts and replication in 8,227 individuals from seven independent cohorts. We identified five genome-wide significant (GWS, P≤5·0×10-8) SNPs annotated to four distinct loci. In addition, we found two additional loci that were significantly replicated, but results of combined meta-analysis fell just below the genome wide significance threshold. The four novel associated genetic loci were located in/near TGFA (rs2862851), PIK3R1 (rs10471753), SLBP/FGFR3 (rs2236995), and TREH/DDX6 (rs496547), while the other two (DOT1L and SUPT3H/RUNX2) were previously identified. A systematic prioritization for underlying causal genes was performed using diverse lines of evidence. Exome sequencing data (n = 2,050 individuals) indicated that there were no rare exonic variants that could explain the identified associations. In addition, TGFA, FGFR3 and PIK3R1 were differentially expressed in OA cartilage lesions versus non-lesioned cartilage in the same individuals. In conclusion, we identified four novel loci (TGFA, PIK3R1, FGFR3 and TREH) and confirmed two loci known to be associated with cartilage thickness.The identified associations were not caused by rare exonic variants. This is the first report linking TGFA to human OA, which may serve as a new target for future therapies.

Genome-wide association and functional studies identify a role for IGFBP3 in hip osteoarthritis.

OBJECTIVES: To identify genetic associations with hip osteoarthritis (HOA), we performed a meta-analysis of genome-wide association studies (GWAS) of HOA. METHODS: The GWAS meta-analysis included approximately 2.5 million imputed HapMap single nucleotide polymorphisms (SNPs). HOA cases and controls defined radiographically and by total hip replacement were selected from the Osteoporotic Fractures in Men (MrOS) Study and the Study of Osteoporotic Fractures (SOF) (654 cases and 4697 controls, combined). Replication of genome-wide significant SNP associations (p ≤5×10(-8)) was examined in five studies (3243 cases and 6891 controls, combined). Functional studies were performed using in vitro models of chondrogenesis and osteogenesis. RESULTS: The A allele of rs788748, located 65 kb upstream of the IGFBP3 gene, was associated with lower HOA odds at the genome-wide significance level in the discovery stage (OR 0.71, p=2×10(-8)). The association replicated in five studies (OR 0.92, p=0.020), but the joint analysis of discovery and replication results was not genome-wide significant (p=1×10(-6)). In separate study populations, the rs788748 A allele was also associated with lower circulating IGFBP3 protein levels (p=4×10(-13)), suggesting that this SNP or a variant in linkage disequilibrium could be an IGFBP3 regulatory variant. Results from functional studies were consistent with association results. Chondrocyte hypertrophy, a deleterious event in OA pathogenesis, was largely prevented upon IGFBP3 knockdown in chondrocytes. Furthermore, IGFBP3 overexpression induced cartilage catabolism and osteogenic differentiation. CONCLUSIONS: Results from GWAS and functional studies provided suggestive links between IGFBP3 and HOA.

Bone mineral density and chronic lung disease mortality: the rotterdam study.

CONTEXT: Low bone mineral density (BMD) has been associated with increased all-cause mortality. Cause-specific mortality studies have been controversial. OBJECTIVE: The aim of the study was to investigate associations between BMD and all-cause mortality and in-depth cause-specific mortality. DESIGN AND SETTING: We studied two cohorts from the prospective Rotterdam Study (RS), initiated in 1990 (RS-I) and 2000 (RS-II) with average follow-up of 17.1 (RS-I) and 10.2 (RS-II) years until January 2011. Baseline femoral neck BMD was analyzed in SD values. Deaths were classified according to International Classification of Diseases into seven groups: cardiovascular diseases, cancer, infections, external, dementia, chronic lung diseases, and other causes. Gender-stratified Cox and competing-risks models were adjusted for age, body mass index, and smoking. PARTICIPANTS: The study included 5779 subjects from RS-I and 2055 from RS-II. MAIN OUTCOME MEASUREMENTS: We measured all-cause and cause-specific mortality. RESULTS: A significant inverse association between BMD and all-cause mortality was found in males [expressed as hazard ratio (95% confidence interval)]: RS-I, 1.07 (1.01-1.13), P = .020; RS-II, 1.31 (1.12-1.55), P = .001); but it was not found in females: RS-I, 1.05 (0.99-1.11), P = .098; RS-II, 0.91 (0.74-1.12), P = .362. An inverse association with chronic lung disease mortality was found in males [RS-I, 1.75 (1.34-2.29), P < .001; RS-II, 2.15 (1.05-4.42), P = .037] and in RS-I in females [1.72 (1.16-2.57); P = .008], persisting after multiple adjustments and excluding prevalent chronic obstructive pulmonary disease. A positive association between BMD and cancer mortality was detected in females in RS-I [0.89 (0.80-0.99); P = .043]. No association was found with cardiovascular mortality. CONCLUSIONS: BMD is inversely associated with mortality. The strong association of BMD with chronic lung disease mortality is a novel finding that needs further analysis to clarify underlying mechanisms.

Genome-wide association study for radiographic vertebral fractures: a potential role for the 16q24 BMD locus.

Vertebral fracture risk is a heritable complex trait. The aim of this study was to identify genetic susceptibility factors for osteoporotic vertebral fractures applying a genome-wide association study (GWAS) approach. The GWAS discovery was based on the Rotterdam Study, a population-based study of elderly Dutch individuals aged > 55 years; and comprising 329 cases and 2666 controls with radiographic scoring (McCloskey­Kanis) and genetic data. Replication of one top-associated SNP was pursued by de-novo genotyping of 15 independent studies across Europe, the United States, and Australia and one Asian study. Radiographic vertebral fracture assessment was performed using McCloskey­Kanis or Genant semi-quantitative definitions. SNPs were analyzed in relation to vertebral fracture using logistic regression models corrected for age and sex. Fixed effects inverse variance and Han­Eskin alternative random effects meta-analyses were applied. Genome-wide significance was set at p < 5 × 10− 8. In the discovery, a SNP (rs11645938) on chromosome 16q24 was associated with the risk for vertebral fractures at p = 4.6 × 10− 8. However, the association was not significant across 5720 cases and 21,791 controls from 14 studies. Fixed-effects meta-analysis summary estimate was 1.06 (95% CI: 0.98­1.14; p = 0.17), displaying high degree of heterogeneity (I2 = 57%; Qhet p = 0.0006). Under Han­Eskin alternative random effects model the summary effect was significant (p = 0.0005). The SNP maps to a region previously found associated with lumbar spine bone mineral density (LS-BMD) in two large meta-analyses from the GEFOS consortium. A false positive association in the GWAS discovery cannot be excluded, yet, the low-powered setting of the discovery and replication settings (appropriate to identify risk effect size > 1.25) may still be consistent with an effect size < 1.10, more of the type expected in complex traits. Larger effort in studies with standardized phenotype definitions is needed to confirm or reject the involvement of this locus on the risk for vertebral fractures.

High bone mineral density and fracture risk in type 2 diabetes as skeletal complications of inadequate glucose control: the Rotterdam Study.

OBJECTIVE: Individuals with type 2 diabetes have increased fracture risk despite higher bone mineral density (BMD). Our aim was to examine the influence of glucose control on skeletal complications. RESEARCH DESIGN AND METHODS: Data of 4,135 participants of the Rotterdam Study, a prospective population-based cohort, were available (mean follow-up 12.2 years). At baseline, 420 participants with type 2 diabetes were classified by glucose control (according to HbA1c calculated from fructosamine), resulting in three comparison groups: adequately controlled diabetes (ACD; n = 203; HbA1c <7.5%), inadequately controlled diabetes (ICD; n = 217; HbA1c ≥ 7.5%), and no diabetes (n = 3,715). Models adjusted for sex, age, height, and weight (and femoral neck BMD) were used to test for differences in bone parameters and fracture risk (hazard ratio [HR] [95% CI]). RESULTS: The ICD group had 1.1-5.6% higher BMD, 4.6-5.6% thicker cortices, and -1.2 to -1.8% narrower femoral necks than ACD and ND, respectively. Participants with ICD had 47-62% higher fracture risk than individuals without diabetes (HR 1.47 [1.12-1.92]) and ACD (1.62 [1.09-2.40]), whereas those with ACD had a risk similar to those without diabetes (0.91 [0.67-1.23]). CONCLUSIONS: Poor glycemic control in type 2 diabetes is associated with fracture risk, high BMD, and thicker femoral cortices in narrower bones. We postulate that fragility in apparently "strong" bones in ICD can result from microcrack accumulation and/or cortical porosity, reflecting impaired bone repair.

Bone parameters across different types of hip osteoarthritis and their relationship to osteoporotic fracture risk.

OBJECTIVE: The atrophic type of hip osteoarthritis (OA) is characterized by cartilage degradation without the formation of osteophytes. Individuals with atrophic OA have been less well studied, and it is unknown whether this OA type differs from the osteophytic types with regard to bone tissue. The purpose of this study was to examine bone mineral density (BMD), hip structural properties, and fracture risk in individuals with the atrophic type of OA as compared to those with the osteophytic types (normotrophic/hypertrophic) as well as individuals without OA. METHODS: This study is part of the Rotterdam Study, a large prospective population-based cohort study. We examined 5,006 participants who had been assessed for OA, BMD, and geometric measures at baseline and for incident nonvertebral osteoporotic fractures (mean followup 9.6 years). We estimated the differences in bone characteristics between the OA groups and the controls (no joint space narrowing or osteophytes). Cox proportional hazards regression was used to calculate osteoporotic fracture risk. RESULTS: Participants with atrophic OA had systemically lower BMD as compared to those with normotrophic OA and as compared to the controls (6.5% and 9% for total body BMD; 4% and 5% for skull BMD, respectively). Participants with osteophytic OA had ∼4% and ∼5% higher total body and skull BMD, respectively, a wider femoral neck, and greater bone strength (12% and 5% higher section modulus, respectively) as compared to the controls or to those with atrophic OA. The risk of osteoporotic fractures was almost 50% higher in those with atrophic OA as compared to the controls (hazard risk 1.48, P = 0.008). This difference was not explained by differences in the BMD, number of falls, degree of disability, or use of corticosteroids. CONCLUSION: Individuals with atrophic hip OA have an increased risk of osteoporotic fractures that is not fully explained by systemically lower BMD as compared to controls.

Scheuermann disease: evaluation of radiological criteria and population prevalence.

STUDY DESIGN: Observational population-based study. OBJECTIVE: To determine the prevalence of radiographical Scheuermann disease in a Dutch population and evaluate the consistency of diagnostic criteria. SUMMARY OF BACKGROUND DATA: Scheuermann disease is a form of osteochondrosis characterized by increased posterior rounding of the thoracic spine with structural vertebral deformity. Different expert opinion-based radiological criteria exist, yet these have not been validated. The prevalence in the general population reported ranged from 1% to 10%. METHODS: Lateral spine radiographs of 2753 Rotterdam Study participants (aged 45-89 yr) were assessed for Scheuermann disease using Sørensen and Sachs' radiographical criteria in 2 phases. Cohen κ statistics were calculated for interrater agreement. Prevalence estimates were calculated and sex differences were tested with Pearson χ test. We evaluated whether varying the kyphosis angle criterion would change the prevalence estimate. RESULTS: A total of 677 (24.6%) individuals had endplate irregularities and 140 (5.1%) individuals had vertebral wedging. Abnormalities were significantly more prevalent among males (P < 0.05). The interrater agreement κ statistics were 78.8% for vertebral wedging and 79.4% for endplate irregularity. A total of 127 individuals had both criteria, of which 111 had a kyphosis angle greater than 45°, resulting in a prevalence of 4.0% (95% confidence interval [CI]: 3.3%-4.7%). The disease prevalence was 4.5% in males versus 3.6% in females, yet this difference was not statistically significant (P = 0.23). Adjustment of the kyphosis angle criterion from 45° to 40° or 35° increased the number of cases marginally, corresponding to prevalence estimates not significantly different from the estimates using original criteria (4.2% [95% CI: 3.3%-4.7%] and 4.4% [95% CI: 3.6%-5.2%]). CONCLUSION: Our results revealed a prevalence of 4.0% of radiographical Scheuermann disease in Dutch individuals aged 45 years and older. Although there is no current "gold standard" for the radiographical definition, standardized scoring of independent features resulted in substantial interobserver agreement, and different applications of diagnostic criteria did not significantly alter the classification.

Genome-wide association and functional studies identify the DOT1L gene to be involved in cartilage thickness and hip osteoarthritis.

Hip osteoarthritis (HOA) is one of the most disabling and common joint disorders with a large genetic component that is, however, still ill-defined. To date, genome-wide association studies (GWAS) in osteoarthritis (OA) and specifically in HOA have yielded only few loci, which is partly explained by heterogeneity in the OA definition. Therefore, we here focused on radiographically measured joint-space width (JSW), a proxy for cartilage thickness and an important underlying intermediate trait for HOA. In a GWAS of 6,523 individuals on hip-JSW, we identified the G allele of rs12982744 on chromosome 19p13.3 to be associated with a 5% larger JSW (P = 4.8 × 10(-10)). The association was replicated in 4,442 individuals from three United Kingdom cohorts with an overall meta-analysis P value of 1.1 × 10(-11). The SNP was also strongly associated with a 12% reduced risk for HOA (P = 1 × 10(-4)). The SNP is located in the DOT1L gene, which is an evolutionarily conserved histone methyltransferase, recently identified as a potentially dedicated enzyme for Wnt target-gene activation in leukemia. Immunohistochemical staining of the DOT1L protein in mouse limbs supports a role for DOT1L in chondrogenic differentiation and adult articular cartilage. DOT1L is also expressed in OA articular chondrocytes. Silencing of Dot1l inhibited chondrogenesis in vitro. Dot1l knockdown reduces proteoglycan and collagen content, and mineralization during chondrogenesis. In the ATDC5 chondrogenesis model system, DOT1L interacts with TCF and Wnt signaling. These data are a further step to better understand the role of Wnt-signaling during chondrogenesis and cartilage homeostasis. DOT1L may represent a therapeutic target for OA.

Serum C reactive protein levels and genetic variation in the CRP gene are not associated with the prevalence, incidence or progression of osteoarthritis independent of body mass index.

OBJECTIVE: To study the relationship between serum C reactive protein (CRP) levels, genetic variation in the CRP gene and the prevalence, incidence and progression of radiographic osteoarthritis (ROA) in the Rotterdam Study-I (RS-I). A systematic review of studies assessing the relationship between osteoarthritis (OA) and CRP levels was also performed. METHODS: The association between CRP levels and genetic variation in the CRP gene and ROA was examined in 861 patients with hand OA, 718 with knee OA, 349 with hip OA and 2806 controls in the RS-I using one-way analysis of covariance and logistic regression, respectively. PubMed was searched for articles published between January 1992 and August 2009 assessing the relationship between CRP levels and OA. RESULTS: In RS-I the prevalence of knee OA, but not hip OA or hand OA, was associated with 14% higher serum CRP levels compared with controls (p=0.001). This association disappeared after adjustment for age and especially body mass index (BMI) (p=0.33). Genetic variation of the CRP gene was not consistently associated with the prevalence, incidence or progression of OA within RS-I. The systematic review included 18 studies (including RS-I) on serum CRP levels and the prevalence, incidence or progression of OA. Consistently higher crude CRP levels were found in cases of prevalent knee OA compared with controls. No association was observed between serum CRP levels and the prevalence of knee OA following adjustment for BMI (n=3 studies, meta-analysis p value=0.61). CONCLUSION: There is no evidence of association between serum CRP levels or genetic variation in the CRP gene with the prevalence, incidence or progression of OA independent of BMI.