Recommendations for standardization and phenotype definitions in genetic studies of osteoarthritis: the TREAT-OA consortium

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. We investigated whether different OA definitions result in different association results by creating various hip OA definitions in one large population based cohort (the Rotterdam Study I (RSI)) and testing those for association with gender, age and body mass index using one-way ANOVA. For ROA, we standardized the hip-, knee- and hand ROA definitions and calculated prevalence's of ROA before and after standardization in nine 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 SOA phenotypes (knee, hip and hand) used a different definition and/or assessment of OA status. For knee-, hip- and hand ROA five, four and seven different definitions were used, respectively. Different hip ROA definitions do lead to different association results. For example, we showed in the RSI that hip OA defined as "at least definite joint space narrowing (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 ROA definitions. Before standardization a wide range of ROA prevalence's was observed in the nine cohorts studied. After standardization the range in prevalence of knee- and hip ROA was small.

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.

New insights into the natural course of knee osteoarthritis: early regulation of cytokines and growth factors, with emphasis on sex-dependent angiogenesis and tissue remodeling. A pilot study

OBJECTIVE

This study was conducted to identify cytokine profiles associated with radiographic phenotypes of knee osteoarthritis (rKOA) with a focus on early stage of the disease.

METHODS

The pilot population study involved 60 middle-aged patients (mean age 50 ± 7.3y.). Standardized weight-bearing anteroposterior and axial radiographs were used to assess rKOA severity in tibiofemoral (TFJ) of patellofemoral joint (PFJ) by grading system (grades 0-3). Luminex (xMAP^®) technology was used to simultaneously assess 60 biomarkers (BMs).

RESULTS

Several pathways of angiogenic (CXCL10/IP-10, FGF1/2, PDGF-AA/BB, ANG1, RANTES), tissue remodeling/fibrosis (MMP1/3, TIMP2/3/4, TGFβ), and fat tissue (leptin) BMs associated with rKOA severity already in very early phase (grade 1). We identified several sets of cytokines as key markers of early knee osteoarthritis (KOA) predicting radiographic features in logistic-regression models (AUC = 0.80-0.97). Marked sex-specificity of rKOA course was detected: upregulation of angiogenesis dominated in females, whereas the activation of tissue remodeling was dominant in males. Several of these shifts, e.g., decrease of CXCL10/IP-10, took place only in grade 1 KOA and disappeared or reversed in later stages. OA of different knee-joint compartments has distinct profiles of cytokines. A broad list of BMs (TIMP2/3/4, MMP1/3, TGFβ1/2, vWF-A2, sE-selectin and leptin) associated with OA in the PFJ.

CONCLUSION

Our results demonstrate that substantial and time-limited shifts in the angiogenic and TIMP/MMP systems occur in the early stage of KOA. Our study findings highlight the sex-, grade- and compartment-dependent shifts in above processes. The data may contribute to the individualized prevention of KOA in the future.

Missense single nucleotide polymorphism of the ADAM12 gene is associated with radiographic knee osteoarthritis in middle-aged Estonian cohort

OBJECTIVE

One of the recognized candidate genes of osteoarthritis (OA) is the ADAM metallopeptidase domain 12 (meltrin alpha) gene. We investigated the potential role of two single nucleotide polymorphisms (SNP) of the ADAM12 gene in susceptibility to radiographic knee OA and its progression in an Estonian cohort.

METHODS

The rs3740199 and rs1871054 polymorphisms were genotyped according to restriction fragment polymorphism in a population-based cohort consisting of 189 subjects selected from the age group 32-55 years. The radiological features of OA were measured in the tibio- and patellofemoral joints (PFJ). The X-ray investigation was repeated 3 years later for estimation of OA progression.

RESULTS

We found statistically significant association between rs3740199 polymorphism and patellofemoral OA in male patients (P=0.014), genetic risk was mostly related to CC homozygosity. The same SNP also affected the presence of advanced grade (II+III) osteophytes in the whole group (P=0.042) and the occurrence of osteophytes on the patellar margins in the PFJ (P=0.046). In OA progression the most significant association was found between joint space narrowing of the tibiofemoral joint and rs3740199 SNP in women (P=0.018). The rs1871054 polymorphism was not related to OA susceptibility or to progression traits. In our study the haplotype GC (rs3740199/rs1871054) was associated with reduced risk for development of osteophytes in the PFJ (P=0.041).

CONCLUSIONS

We conclude that rs3740199 polymorphism may affect occurrence of knee OA and its progression. We also hypothesize that the genetic contribution of ADAM12 to OA is remarkably gender-dependent and anatomical site-specific.

Risk Assessment of the Progression of Early Knee Osteoarthritis by Collagen Neoepitope C2C: A Longitudinal Study of an Estonian Middle-Aged Cohort

One of the unmet needs to be addressed is prognostic biomarkers for early knee osteoarthritis (kOA). We aimed to study the association of urinary collagen type-II C-terminal cleavage neoepitope (uC2C) with the emergence and progression of kOA. The longitudinal data of 330 subjects (aged 32-60 years) from an Estonian population-based cohort were used. The radiographic progression was evaluated by the grading system of Nagaosa et al. of knee compartments at baseline and three years later. The emerging kOA consisted of subjects with developing osteophytes or joint space narrowing, whereas kOA progressors showed aggravation of radiographic grade. Baseline uC2C levels were measured by the IBEX-uC2C assay. At baseline, the subjects were middle-aged (mean age, 47.6 years) and overweight (mean BMI, 28.0 kg/m2), and the majority of them (51.2%) had a diagnosis of kOA grade 1. Multiple logistic regression models adjusted for sex, age, and BMI were used for risk calculations. We demonstrate that increased uC2C accurately predicted the risk of emerging of kOA (OR = 5.87 (1.71-20.22); AUC = 0.79) compared with controls without radiographic kOA over 12 years. However, the most accurate prediction of progression by the biomarker was found in women (OR = 23.0 (2.2-245), AUC = 0.91). In conclusion, uC2C may be a promising candidate as a prognostic biomarker for kOA progression, particularly of emerging kOA in women.