What are the genetic changes related to osteogenesis imperfecta ?
Mutations in the COL1A1, COL1A2, CRTAP, and P3H1 genes cause osteogenesis imperfecta.  Mutations in the COL1A1 and COL1A2 genes are responsible for more than 90 percent of all cases of osteogenesis imperfecta. These genes provide instructions for making proteins that are used to assemble type I collagen. This type of collagen is the most abundant protein in bone, skin, and other connective tissues that provide structure and strength to the body.  Most of the mutations that cause osteogenesis imperfecta type I occur in the COL1A1 gene. These genetic changes reduce the amount of type I collagen produced in the body, which causes bones to be brittle and to fracture easily. The mutations responsible for most cases of osteogenesis imperfecta types II, III, and IV occur in either the COL1A1 or COL1A2 gene. These mutations typically alter the structure of type I collagen molecules. A defect in the structure of type I collagen weakens connective tissues, particularly bone, resulting in the characteristic features of osteogenesis imperfecta.  Mutations in the CRTAP and P3H1 genes are responsible for rare, often severe cases of osteogenesis imperfecta. Cases caused by CRTAP mutations are usually classified as type VII; when P3H1 mutations underlie the condition, it is classified as type VIII. The proteins produced from these genes work together to process collagen into its mature form. Mutations in either gene disrupt the normal folding, assembly, and secretion of collagen molecules. These defects weaken connective tissues, leading to severe bone abnormalities and problems with growth.  In cases of osteogenesis imperfecta without identified mutations in one of the genes described above, the cause of the disorder is unknown. These cases include osteogenesis imperfecta types V and VI. Researchers are working to identify additional genes that may be responsible for these conditions.