For example, 85–90% of osteogenesis imperfecta (OI) cases are due to mutations in the genes encoding type 1 collagen (i.e. COL1A1 and COL1A2) 20, with the remaining 10–15% of OI cases being caused by mutations affecting genes involved in post‐translational processing of collagen [e.g. cartilage‐associated protein (CRTAP)] 21, osteoblast differentiation and function (e.g. WNT1) 19, 22, or bone mineralization [e.g. interferon‐induced transmembrane protein 5 (IFITM5)] (Table 1) 23, 24. The gene discussed is COL1A2; the disease is osteogenesis imperfecta.