SFRP1 and arthritic joint disease: Before arthritis onset at day 8, OS/BS was inversely correlated with SOST (Fig. 6A, r = −1, p < 0.02) but not with DKK1 or SFRP1 (Table S2, r = −0.50, p = 0.45 for both), suggesting that high SOST at day 8 correlated with low osteoblast activity.