Brittle bone disease

Definition

Osteogenesis imperfecta is a condition causing extremely fragile bones.

Alternative Names

Causes

Osteogenesis imperfecta (OI) is a congenital disease, meaning it is present at birth. It is frequently caused by defect in the gene that produces type 1 collagen, an important building block of bone. There are many different defects that can affect this gene. The severity of OI depends on the specific gene defect.

OI is an autosomal dominant disease. That means if you have one copy of the gene, you will have the disease. Most cases of OI are inherited from a parent, although some cases are the result of new genetic mutations.

A person with OI has a 50% chance of passing on the gene and the disease to their children.

Symptoms

All people with OI have weak bones, which makes them susceptible to fractures. Persons with OI are usually below average height ( short stature). However, the severity of the disease varies greatly.

The classic symptoms include:

• Blue tint to the whites of their eyes (blue sclera)
• Multiple bone fractures
• Early hearing loss (deafness)

Because type I collagen is also found in ligaments, persons with OI often have loose joints (hypermobility) and flat feet. Some types of OI also lead to the development of poor teeth.

Symptoms of more severe forms of OI may include:

• Bowed legs and arms
• Kyphosis (S-curve spine)
• Scoliosis

Exams and Tests

OI is usually suspected in children whose bones break with very little force. A physical examination may show that the whites of their eyes have a blue tint.

A definitive diagnosis may be made using a skin punch biopsy. Family members may be given a DNA blood test.

If there is a family history of OI, chorionic villus sampling may be done during pregnancy to determine if the baby has the condition. However, because so many different mutations can cause OI, some forms cannot be diagnosed with a genetic test.

The severe form of type II osteogenesis imperfecta can be seen on ultrasound when the fetus is as young as 16 weeks.

Treatment

There is not yet a cure for this disease. However, specific therapies can reduce the pain and complications associated with OI.

Bisphosphonates are drugs that have been used to treat osteoporosis. They have proven to be very valuable in the treatment of OI symptoms, particularly in children. These drugs can increase the strength and density of bone in persons with OI. They have been shown to greatly reduce bone pain and fracture rate (especially in the bones of the spine).

Low impact exercises such as swimming keep muscles strong and help maintain strong bones. Such exercise can be very beneficial for persons with OI and should be encouraged.

In more severe cases, surgery to place metal rods into the long bones of the legs may be considered to strength the bone and reduce the risk of fracture. Bracing can also be helpful for some people.

Reconstructive surgery may be needed to correct any deformities. Such treatment is important because deformities (such as bowed legs or a spinal problem) can significantly affect a person's ability to move or walk.

Regardless of treatment, fractures will occur. Most fractures heal quickly. Time in a cast should be limited since bone loss (disuse osteoporosis) may occur when you do not use a part of your body for a period of time.

Many children with OI develop body image problems as they enter their teenage years. A social worker or psychologist can help them adapt to life with OI.

Outlook (Prognosis)

How well a person does depends on the type of OI they have.

• Type I, or mild OI, is the most common form. Persons with this type can live a normal lifespan.
• Type II is a severe form that is usually leads to death in the first year of life.
• Type III is also called severe OI. Persons with this type have many fractures starting very early in life and can have severe bone deformities. Many become wheelchair bound and usually have a somewhat shortened life expectancy.
• Type IV, or moderately severe OI, is similar to type I, although persons with type IV often need braces or crutches to walk. Life expectancy is normal or near normal.

There are other types of OI, but they occur very infrequently and most are considered subtypes of the moderately severe form (type IV).

Possible Complications

Complications are largely based on the type of OI present. They are often directly related to the problems with weak bones and multiple fractures.

Complications may include:

• Hearing loss (common in type I and type III)
• Heart failure (type II)
• Respiratory problems and pneumonias due to chest wall deformities
• Spinal cord or brain stem problems
• Permanent deformity

When to Contact a Medical Professional

Severe forms are usually diagnosed early in life, but mild cases may not be noted until later in life. Make an appointment with your health care provider if you or your child have symptoms of this condition.

Prevention

Genetic counseling is recommended for couples considering pregnancy if there is a personal or family history of this condition.