The cystatin C-deficient mice were more prone to develop arthritis with a significantly higher incidence compared to the wild type controls (Figure 1A, Table 1) arguing for a protective role of cystatin C. Furthermore, cystatin C-deficient mice developed arthritis earlier than the wild type control mice, but there was no significant difference in the severity of arthritis as the maximal score was similar among all groups (Figure 1B, Table 1). The gene discussed is CST3; the disease is arthritic joint disease.