Moreover, Fassio et al. [37] demonstrated that the effective treatment of RA patients with certolizumab pegol in combination with MTX was associated with an increase in serum levels of PINP and a decrease in serum levels of C-terminal cross-linking telopeptides of type I collagen caused by cathepsin K, suggesting increased synthesis and decreased degradation of the bone matrix components, respectively. The gene discussed is CTSK; the disease is rheumatoid arthritis.