The International Osteoporosis Foundation (IOF) and the International Federation of Clinical Chemistry (IFCC) Working Group on the Standardization of Bone Markers recommended type β-I collagen carboxy-terminal peptide (β-CTX) and type I procollagen amino-terminal peptide (P1NP) as bone turnover markers (BTMs). The gene discussed is COL1A2; the disease is osteoporosis.