Pyruvate kinase M2 (PKM2) is more highly expressed in the lining layer (1.16 ± 0.33 OA vs 2.74 ± 0.14 RA), sublining layer (0.78 ± 0.28 OA vs 2.5 ± 0.16 RA) and vasculature (0.78 ± 0.28 OA vs 3.02 ± 0.19 RA) (all p < 0.005) of RA synovial tissue compared to OA. This evidence concerns the gene PKM and rheumatoid arthritis.