Osteogenesis imperfecta (OI) is a condition that is caused by a genetic defect. A person who has this defect has either less collagen or a poorer quality of collagen than normal, leading to weak bones that fracture easily. The mutated genes (the specific osteogenesis imperfecta causes) are known as the COL1A1 and COL1A2 genes.

What Causes Osteogenesis Imperfecta?

The cause of osteogenesis imperfecta (OI) is a genetic defect that affects the body's production of collagen. Collagen is the major protein of the body's connective tissue and can be likened to the framework around which a building is constructed. In osteogenesis imperfecta, a person has either less collagen than normal, or a poorer quality of collagen than normal, and this leads to weak bones that fracture easily.   For people who have children with osteogenesis imperfecta, it is important to understand that nothing you or your spouse did during conception or pregnancy caused this condition in your child. Osteogenesis imperfecta has been prevalent for thousands of years.   Genetic counseling, which is available at most hospitals, may help you understand the type of osteogenesis imperfecta your child has. If you are thinking about having more children, you should consider contacting a geneticist, who can help determine the probability of recurrence of OI in your family.  

The Role of Genetics

In most cases, the osteogenesis imperfecta cause is a dominant genetic defect (known as autosomal dominant) in the genes responsible for making collagen. Some children with osteogenesis imperfecta inherit the disorder from a parent. Other children are born with OI even though there is no family history of the disorder. In these children, the genetic defect occurred as a spontaneous mutation.   Because the defect that leads to osteogenesis imperfecta -- whether inherited or due to a spontaneous mutation -- is usually dominant, a person with OI has a 50 percent chance of passing on the disorder to each of his or her children.   Rarely, osteogenesis imperfecta can be inherited in an autosomal recessive pattern, which means two copies of the gene must be altered for a person to be affected by the disorder. Most often, the parents of a child with an autosomal recessive disorder are not affected but are carriers of one copy of the altered gene.   Genetic counselors can help people with osteogenesis imperfecta and their family members further understand OI genetics and the possibility of recurrence, and assist in prenatal diagnosis for those who wish to exercise that option.