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Osteogenesis imperfecta (OI) is a genetic disorder characterized by bones that break easily, often from little or no apparent cause. A classification system of different types of OI is commonly used to help describe how severely a person with OI is affected. For example, a person may have just a few or as many as several hundred fractures in a lifetime.
Although the number of people affected with OI in the United States is unknown, the best estimate suggests a minimum of 20,000 and possibly as many as 50,000.
OI is caused by genetic defects that affect the body’s ability to make strong bones. 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 dominant (classical) OI, a person has either too little type 1 collagen or a poor quality of type 1 collagen caused by a mutation in one of the type 1 collagen genes. In recessive OI, mutations in other genes interfere with collagen production. The result in all cases is weak bones that break easily.
It is often possible to diagnose OI based solely on clinical features. Clinical geneticists can perform biochemical (collagen) or molecular (DNA) tests that can help confirm a diagnosis of OI in some situations.
These tests generally require several weeks before results are known. Both the collagen biopsy test and the DNA test are thought to detect nearly 90 percent of all type 1 collagen mutations.
A positive collagen type I test confirms the diagnosis of dominant OI, but a negative result leaves open the possibility that:
Therefore, a negative type 1 collagen study does not rule out OI. When a type 1 collagen mutation is not found, other DNA tests can check for recessive forms.
The characteristic features of OI vary greatly from person to person, even among people with the same type of OI and even within the same family. Not all characteristics are evident in each case. The majority of OI cases (possibly 85 to 90 percent) are caused by a dominant mutation in a gene coding for type 1 collagen (Types I, II, III, and IV in the following list). Types V and VI do not have a type 1 collagen mutation, but the genes causing them have not yet been identified. Types VII and VIII are newly discovered forms that are inherited in a recessive manner, and the genes causing these two types have been identified. The general features of each of the known types of OI, which vary in characteristics and severity, are as follows:
By studying the appearance of OI bone under the microscope, investigators noticed that some people who are clinically within the Type IV group had a distinct pattern to their bone. When they reviewed the full medical history of these people, they found the groups had other features in common. They named these groups Type V and Type VI OI. The mutations causing these forms of OI have not been identified, but people in these two groups do not have mutations in the type 1 collagen genes.
After years of research, in 2006, scientists discovered two forms of OI that are inherited in a recessive manner. Genes that affect collagen formation cause both types. The discovery of these new forms of OI provides information for people who have severe or moderately severe OI but do not have a primary collagen mutation.
Most cases of OI (85 to 90 percent) are caused by a dominant genetic defect. This means that only one copy of the mutation-carrying gene is necessary for the child to have OI. A person with a form of OI caused by a dominant mutation has a 50 percent chance of passing on the disorder to each of his or her children.
Some children who have the dominant form of OI inherit the disorder from a parent. Other children are born with the dominant form of OI even though there is no family history of the disorder. In these children, the genetic defect occurred as a spontaneous mutation.
Approximately 10 to 15 percent of OI cases are the result of a recessive mutation. In this situation, the parents do not have OI, but both carry the mutation in their genes. To inherit recessive OI, the child must receive a copy of the mutation from both parents.
The parents of a child with recessive OI have a 25-percent chance per pregnancy of having another child with OI. Siblings of a person with recessive OI have a 50-percent chance of being a carrier of the recessive gene. DNA testing is available to help parents and siblings determine if they are carriers of this type of gene mutation.
If one parent has OI because of a recessive mutation, 100 percent of their children will be carriers of the recessive OI mutation. Whether any of these children will have OI will depend on the genes inherited from the other parent. Genetic counselors can help people with OI and their family members understand OI genetics and the possibility of recurrence, and they can assist in prenatal diagnosis for those who wish to exercise that option. For more information on OI inheritance, see the fact sheet, Genetics, from the Osteogenesis Imperfecta Foundation.
There is not yet a cure for OI. Treatment is directed toward preventing or controlling the symptoms, maximizing independent mobility, and developing optimal bone mass and muscle strength. Care of fractures, extensive surgical and dental procedures, and physical therapy are often recommended for people with OI. Use of wheelchairs, braces, and other mobility aids is common, particularly (although not exclusively) among people with more severe types of OI.
Doctors frequently consider a surgical procedure called “rodding” for people with OI. This treatment involves inserting metal rods through the length of the long bones to strengthen them. The treatment also prevents or corrects deformities. For more information, see the Osteogenesis Imperfecta Foundation’s fact sheet, Rodding Surgery.
Scientists are exploring several medications and other treatments for their potential use to treat OI. These include growth hormone treatment, intravenous and oral drugs called bisphosphonates, an injected drug called teriparatide (for adults only), and gene therapies. It is not clear whether people with recessive OI and those with dominant OI will respond to these treatments in the same manner. The OI Foundation can provide current information on research studies and experimental treatments to help individuals with OI decide whether to participate in clinical trials.
People with OI are encouraged to exercise as much as possible to promote muscle and bone strength, which can help prevent fractures. Swimming and water therapy are common exercise choices for people with OI, as water allows independent movement with little risk of fracture. For those who are able, walking (with or without mobility aids) is excellent exercise. People with OI should consult their doctor or physical therapist to discuss appropriate and safe exercise.
Children and adults with OI also will benefit from maintaining a healthy weight, eating a nutritious diet, and avoiding activities such as smoking, excessive alcohol and caffeine consumption, and taking steroid medications—all of which may deplete bone and exacerbate bone fragility. For more information on nutrition, see the Osteogenesis Imperfecta Foundation’s fact sheet, Nutrition.
The prognosis for a person with OI varies greatly depending on the number and severity of symptoms. Respiratory failure is the most frequent cause of death for people with OI, followed by accidental trauma. Despite numerous fractures, restricted activity, and small stature, most adults and children with OI lead productive and successful lives. They attend school, develop friendships and other relationships, have careers, raise families, participate in sports and other recreational activities, and are active members of their communities.
For more information about osteogenesis imperfecta, contact:
Toll free: 800-981-BONE (2663)
The National Resource Center acknowledges the assistance of the Osteogenesis Imperfecta Foundation in the preparation of this publication.
This publication contains information about medications used to treat the health condition discussed here. When this publication was produced, we included the most up-to-date (accurate) information available. Occasionally, new information on medication is released.
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