The use in the not too distant past of underpowered case–control cohorts in OA genetic studies threw up a large number of genetic associations. WhClear differences in inflammatory gene expression have been identified in the OA joint compared to non-OA controls, with one of the most overtly inflamed tissues being the synovium. Inflammation is less pronounced in the OA synovium in comparison to rheumatoid arthritis (RA) but correlates with both pain and structural decline33 and 34. While the precise cause of synovium inflammation (synovitis) remains to be defined, gene-expression microarray analysis shows increased expression of complement effector genes and a decrease of complement inhibitors in the OA synovium compared to controls35. Further to this, IL-1β has been associated with many of the pathological features of OA. Although IL1R, encoding the IL-1 receptor, is not differentially expressed in normal compared to OA synovial fibroblasts, IL-1R is upregulated at the protein level in OA 36. IL-1β signaling has been shown to modulate expression of 909 out of 3459 genes in primary human articular chondrocytes, including significant induction of numerous chemokines and inflammatory mediators, such as the genes IL11 and CCL5 37. This post-transcriptional upregulation of IL-1R in OA is therefore likely to cause a significant alteration in inflammatory gene expression. In line with this, comparison of OA cartilage to microscopically intact cartilage from individuals without OA identified a distinct upregulation of chemokine and cytokine genes in OA cartilage, including IL8 and LIF