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Osteogenesis Imperfecta +@s-tE-u-!je-nu-sus-+im-(+)pur-!fek-tu

by David D. Sherry, MD, Frank Pessler, MD, PhD

Osteogenesis imperfecta is a hereditary disorder that disrupts the proper formation of bones and makes bones abnormally fragile.

  • Typical symptoms include weak bones that break easily.

  • The diagnosis is based on x-rays.

  • The type that occurs in infancy is lethal.

  • Certain drugs and injections can help strengthen bones.

Osteogenesis imperfecta (OI) is the best known of a group of disorders that disturb bone growth. These disorders are called osteodysplasias. In OI, synthesis of collagen, one of the normal components of bone, is impaired. The bones become weak and break (fracture) easily. There are 4 main types of OI. Other types are rare.

Symptoms

OI can range from mild to severe. Most people with OI have fragile bones, and about 50 to 65% have hearing loss. OI causes the whites of the eyes (sclerae) in some people to turn blue. The blue color appears because the veins beneath the abnormally thin sclerae show through. The sclerae are thinner than normal because collagen has not been formed correctly. Children may have discolored and poorly developed teeth (called dentinogenesis imperfecta) depending on the type of OI. Sometimes heart or lung diseases develop in children with OI.

Type I OI is the mildest type. Some children may have only symptoms of blue sclerae and muscle and joint pain caused by loose joints. Children with this type may have increased risk of fractures during childhood.

Type II OI is the most severe type and causes death. Infants are usually born with many broken bones. The skull may be so soft that the brain is not protected from pressure applied to the head during childbirth. These infants have shortened arms and legs and blue sclerae. Infants with this type can die before childbirth or within the first few days or weeks of life.

Type III OI is the most severe type that does not cause death. Children with this type are very short and have curving of the spine and frequent fractures. This type causes bones to often break after very minor injuries, usually when children begin to walk. These children also have a large skull and a triangular face shape caused by overdevelopment of the head and underdevelopment of the face bones. Chest deformities are common. The color of the sclerae varies.

Type IV OI is a moderate type. Children with this type have bones that fracture easily during childhood before puberty. The sclerae are typically white. Children are short. Children with this type may benefit from treatment.

Diagnosis

  • Genetic tests

  • Prenatal ultrasonography

X-rays may show abnormal bone structure that suggests OI. The removal of a sample of skin for examination under a microscope (biopsy) or to grow a type of connective tissue cells (fibroblasts) in a culture dish is done to confirm the diagnosis. Doctors may analyze certain genes if the diagnosis is not clear.

The most severe and lethal form of OI can be detected in pregnant women by an ultrasound (see Procedures : Ultrasonography).

A test called audiometry (see Hearing Loss and Deafness:Testing) is done often throughout childhood to monitor hearing.

Treatment

  • Bisphosphonates

  • Growth hormones

A type of drug called a bisphosphonate can be given by vein (such as pamidronate) or taken by mouth (such as alendronate) and it may strengthen bones and lessen pain and the frequency of fractures. Growth hormone injections can also help children with types I and IV.

Treatment of broken bones is similar to that for children who do not have the disorder. However, broken bones can become deformed or fail to grow. As a result, body growth can become permanently stunted in children with many broken bones, and deformities are common. Bones may require stabilization with internal metal rods. Physical therapy and occupational therapy help prevent fractures and improve function. Taking measures to avoid even minor injuries can help prevent fractures.

Some children may be helped by a cochlear implant (see Hearing Loss and Deafness:Treatment in children).

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