There are 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 as many as several hundred fractures in a lifetime.
OI is caused by a genetic defect that affects the body's production of collagen, not calcium. 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(Type I), or a poorer quality of collagen than normal(Type II-IV)--leading to weak bones that fracture easily. An easy explination of collagen is this:
Collagen rods in bone are similar to the steel rods that support the building. The minerals including calcium and phosphorous from the blood, that crystallize and surround the rods play the same role as the cement that surrounds and supports steel rods in a building. These minerals give the bones strength while the collagen rods provide resiliency.
It is important to note that the features of OI (fracture frequency, muscle strength, bone and joint alignment) 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. In addition, many people with OI do not fit clearly into one of these four types. Types I to IV OI are determined based on clinical and radiographic data. Researchers are beginning to identify additional types of OI. Two new types of OI, Types V and VI, appear clinically similar to Type IV but have a distinct histology. When working with an individual who has OI, therefore, it is most important to focus on his or her particular abilities, strengths, and weaknesses rather than on his or her OI type.
Signs and symptoms of OI may include frequent fractures; muscle weakness; joint laxity; short stature; blue or gray sclera (whites of the eyes); thin, smooth skin; easy bruising; spinal curvature; bowing of long bones; and excessive sweating and heat intolerance. Some people with OI have a barrel-shaped rib cage and/or a triangular face. Some experience hearing loss, often beginning in early adulthood but in some cases beginning in childhood. Some also have a condition called dentinogenesis imperfecta, which affects the teeth.
Clinical Features
Type I --Most common and usually mildest type of OI. (some type I's have many more fractures than the Type III/IV's)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 and insufficient.
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.
Some Type III will move into the Type IV range with treatment modalities
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.
How Does One Get OI?
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.
Treatment Options
Rodding Surgery- Rods can be surgically placed in long bones that have recurrent fractures and severe bowing. This helps to decrease pain, reduce the incidence of fractures, and enhance functioning, comfort, development and the ability to standand walk. Bisphosphonates- There are two main cell groups in the bone. The osteoblasts, which make bone, and the osteoclasts that break down the bone (bone resorption). Both types of cells are very active, even in the adult, and work together to keep the bone intact and responding to stress. Current knowledge suggests that bisphosphonates slow down the process of bone resorption by shortening the life of the osteoclasts and prolonging the life of the osteoblasts, thus tilting the balance towards the production of bone. The prolonged osteoblast still produces mutant collagen. Thus, the patient is still making "OI bone," but resorbing less of it.
The most common is the IV drug pamidronate. It has also been shown to improve vertebral height and development in kids with compressed vertebral bodies. The long term effects are unknown, therefore it is not recommended in mild cases of OI. This treatment is typically done in the hospital.
Exercise- This is critical in a person with OI. Physical therapy, occupational therapy, and exercise all help to stregnthen a person with OI giving them optimal movement and functioning. It is important to start this as soon as possible. Swimming is a good choice as it is low impact but great for allowing them to use their muscles. Exercise also helps to keep a healthy weight which is important for everyone but especially someone with OI. The less weight, the less stress on the bones.
