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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 types of the disorder,
representing extreme variation in severity from one individual to another. For example, a person may have just a few or a
as many as several hundred fractures in a lifetime.
It is estimated that there are about 20,000 to 50,000
people with Osteogenesis Imperfecta in the United States.
Osteogenesis Imperfecta 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.
The characteristics features of Osteogenesis
Imperfecta vary greatly from person to person--even among people with the same type of OI, and not all characteristics are
evident in each case.
Clinical Features
Type I --
Most common and mildest type of Osteogenesis Imperfecta.
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 of Osteogenesis Imperfecta.
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 Osteogenesis Imperfecta 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 Osteogenesis Imperfecta 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.
Treatment
There is not yet a cure for Osteogenesis Imperfecta. 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. 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.
Several medications and other treatments are being explored for their potential
use to treat OI (see next section PAMIDRONATE TREATMENTS). 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.
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