Moreover, patients with RA were also shown to have a reduced level of markers for bone formation, such as the N-terminal middle molecular fragment of osteocalcin (N-MID) and the total procollagen type I amino-terminal propeptide (T-P1NP), but an increased level of markers for bone absorption, such as the β-C terminal cross-linking telopeptide of type 1 collagen (β-CTX) [13], which collectively reflect the bone loss in RA. The gene discussed is COL1A2; the disease is rheumatoid arthritis.