Animal models of osteogenesis imperfecta and craniofacial development

Introduction Osteogenesis imperfecta (OI) is a human genetic disorder of increased bone fragility and low bone mass. Severity varies widely, ranging from intrauterine fractures and perinatal lethality to very mild forms without fractures. There is variable association of typical extra skeletal manifestations with the disorder, including blue sclera, dentinogenesis imperfecta, hyperlaxity of ligaments and skin, hearing impairment and the presence of Wormian bones on skull radiography1. The most widely used classification of OI distinguished four clinical types2. The most relevant clinical characteristic of all OI t-ypes is bone fragility, the severity of which increases in the order type I < type IV < type III < type II. It is now w-idely recognized that there may be m-any more types of OI than those class-ified by Sillence et al. Some forms of congenital brittle bones have been considered OI and have been added as types V, VI and VII3–5. There is still no perfect consensus about the definition of OI. Plotkin recently proposed defining OI as syndromes resulting from mutations in either COL1A1 or COL1A2 genes, and to group all other syndromes with congenital brittle bones as ‘syndromes resembling OI (SROI)’, pending the identification of their causal mutations6. In the new Nosology and Classification of the Genetic Skeletal disorders7, OI is declined in several forms depending on the severity of the phenotype, whatever the mode of the transmission or the gene involved. We first review the genetic mutations implicated in the eight different types of OI, then, the craniofacial consequences of OI mutations are summarized. * Corresponding author Email: [email protected]