When comparing the ratios of the two TRAcP isoforms (5B/5A) a pronounced difference (p = 0.07) could be noted between seropositive RA (mean ratio 0.714±0.259, median 0.459) and OA (mean ratio 1.384±0.275, median 1.000) patients; the ratios of the seronegative RA patients (mean ratio 1.388±0.680, median 0.909) were on the same level as OA patients but their distribution was more widespread than in OA (RF- standard deviation 2.152, OA 1.35) (Fig 2A). This evidence concerns the gene ACP5 and rheumatoid arthritis.