Definition
Osteogenesis imperfecta (OI) is a genetic disorder characterized by bones that break
easily, often from little or no apparent cause. There are at least four recognized forms
of the disorder, representing extreme variation in severity from one individual to
another. For example, a person may have just a few or as many as several hundred fractures
in a lifetime.
Prevalence
While 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.
Diagnosis
OI is caused by 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 OI, a person has either less
collagen than normal, or a poorer quality of collagen than normal—leading to weak
bones that fracture easily.
It is often, though not always, possible to diagnose OI based solely on clinical
features (see chart). Clinical geneticists can also 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, and approximately 10 to 15
percent of individuals with mild OI who have collagen testing, and approximately 5 percent
of those who have genetic testing, test negative for OI despite having the disorder.
Clinical Features
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—and not all
characteristics are evident in each case. The general features of the four recognized
types of OI, which vary in characteristics and severity, are as follows:
| Type I |
- Most common and mildest type of OI.
- Bones predisposed to fracture. Most fractures occur before puberty.
- Normal or near-normal stature.
- Loose joints and low muscle tone.
- Sclera (whites of the eyes) usually have a blue, purple, or gray tint.
- Triangular face.
- Tendency toward spinal curvature.
- Bone deformity absent or minimal.
- Brittle teeth possible.
- Hearing loss possible, often beginning in early 20s or 30s.
- Collagen structure is normal, but the amount is less than normal.
|
| Type II |
- Most severe form.
- Frequently lethal at or shortly after birth, often due to respiratory problems. In
recent years, some people with Type II have lived into young adulthood.
- Numerous fractures and severe bone deformity.
- Small stature with underdeveloped lungs.
- Collagen is improperly formed.
|
| Type III |
- Bones fracture easily. Fractures often present at birth, and x-rays may reveal healed
fractures that occurred before birth.
- Short stature.
- Sclera have a blue, purple, or gray tint.
- Loose joints and poor muscle development in arms and legs.
- Barrel-shaped rib cage.
- Triangular face.
- Spinal curvature.
- Respiratory problems possible.
- Bone deformity, often severe.
- Brittle teeth possible.
- Hearing loss possible.
- Collagen is improperly formed.
|
| Type IV |
- Between Type I and Type III in severity.
- Bones fracture easily, most before puberty.
- Shorter than average stature.
- Sclera are white or near-white (i.e., normal in color).
- Mild to moderate bone deformity.
- Tendency toward spinal curvature.
- Barrel-shaped rib cage.
- Triangular face.
- Brittle teeth possible.
- Hearing loss possible.
- Collagen is improperly formed.
|
Inheritance Factors
Most cases of OI are caused by a dominant genetic defect. Some children with OI 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—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. Genetic counselors can help people with OI 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. For more information on OI inheritance, see the OI
Foundation fact sheet titled "Genetics."
Treatment
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.
A surgical procedure called "rodding" is frequently considered for
individuals with OI. This treatment involves inserting metal rods through the length of
the long bones to strengthen them and prevent and/or correct deformities. For more
information, see the OI Foundation’s fact sheet on "Rodding
Surgery."
Several medications and other treatments are being explored for
their potential use to treat OI. The OI Foundation can provide current information on
research studies and experimental treatments for OI, as well as information to help
individuals 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. Individuals with OI should consult their physician and/or physical therapist to
discuss appropriate and safe exercise.
Children and adults with OI will also 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 OI Foundation fact
sheet titled "Nutrition."
Prognosis
The prognosis for an individual with OI varies greatly depending on the
number and severity of symptoms. Despite numerous fractures, restricted activity, and
short stature, most adults and children with OI lead productive and successful lives.
This information is brought to
you by the NIH Osteoporosis and Related Bone Diseases~National Resource Center
(ORBD~NRC)
and the Osteogenesis Imperfecta Foundation
National
Institutes of Health
Osteoporosis and Related Bone Diseases
National Resource Center
1232 22nd St., NW
Washington, DC 20037-1292
Tel: 800/624-BONE or 202/223-0344
Fax: 202/293-2356, TYY: 202/466-4315
http://www.osteo.org
E-mail: orbdnrc@nof.org
The National Resource
Center is supported by the National Institute of Arthritis and Musculoskeletal and Skin
Diseases with contributions from the National Institute of Child Health and Human
Development, National Institute of Dental and Craniofacial Research, National Institute of
Environmental Health Sciences, NIH Office of Research on Women’s Health, Office of
Women’s Health, PHS, and the National Institute on Aging. The Resource Center is
operated by the National Osteoporosis Foundation, in collaboration with the Paget
Foundation and the Osteogenesis Imperfecta Foundation.
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