Osteogenesis imperfecta (OI) is a group of rare, inherited disorders with genetic and clinical diversities. With a prevalence of 1:10,000–1:20,000, OI is considered as an “orphan disease.” OI is caused by quantitative or qualitative defects in collagen type 1 or by proteins interacting with collagen type 1. Changes in the amount or in the structure of collagen type 1 result in high bone fragility. Therefore, OI is also known as brittle bone disease.
In severe cases, fracture occurrence starts during the intrauterine or perinatal period leading to multiple fractures of hollow bones and ribs, which results in respiratory insufficiency and death. In contrast, mild OI leads to fewer fractures and in this respect mimics juvenile osteoporosis. Deformity of the skeleton and extraskeletal features such as dentinogenesis imperfecta and blue sclerae are typical signs of OI. Based on these characteristics, Professor David Sillence introduced his classification in 1979. He divided patients into four subgroups, suggesting dominant and recessive genotypes responsible for OI. The original Sillence classification has been expanded to include 11 different types of OI based on genetic alterations [ 1 ]. In respect to the clinical classification of OI, Sillence is (still) golden.