Osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a term for a group of genetic diseases in which the bones are formed improperly, making them fragile and likely to break.This happens when collagen, the fibrous protein material that makes up skin,bone, cartilage, and ligaments, is faulty.

Osteogenesis imperfecta affects equal numbers of males and females. It occursin about one of every 30,000 births. Osteogenesis imperfecta is a genetic disorder, but not everyone who has it received a defective gene from his or hermother or father. Some cases are due to a spontaneous mutation (a permanentdefect in a specific gene) that occurs after birth. A person who has osteogenesis imperfecta due to a spontaneous mutation can then pass on this defectivegene to his or her future offspring.

There are four forms of osteogenesis imperfecta, called Types I through IV. Of these, Type II tends to be the most severe, and usually causes death shortly after birth. Types I, III, and IV have some symptoms in common, but each also has distinctive symptoms. Symptoms include:

  • Weak bones which break(fracture) easily. In some forms of osteogenesis imperfecta, these fracturesoccur even before birth. People with Type I have about 20-40 fractures beforepuberty; people with Type III may have more than 100 fractures before puberty. Fractures usually occur less after puberty, but may increase again in women after menopause.
  • Loose, unstable joints (due to abnormal structureof the ligaments), resulting in a high risk of dislocation.
  • A bluishtinge to the white of the eye (the sclera).
  • A curved and twisted spine (scoliosis).
  • Hearing loss (due to malformation and fractures of thetiny bones in the middle ear which are necessary for hearing).
  • Abnormally fragile, discolored (bluish-yellow) teeth.
  • Shorter-than-normalfinal height, depending on the type of osteogenesis imperfecta. In Type I, height is slightly short or close to normal; in Type III, height is quite abnormal, with growth stopping around three feet; in Type IV, height is somewhat shorter than normal.
  • Thin, fragile skin.
  • A high risk of complications such as hernias and heart valve abnormalities.

Other complications vary according to the type of osteogenesis imperfecta. InType I, the face is often triangular in shape. In Type II, the rib cage maybe abnormally formed, restricting the lungs and causing breathing difficulties. The arms and legs are often shorter than normal, and the bones are bowed.

Osteogenesis imperfecta is usually suspected when a baby has bone fractures for no obvious reason. The bluish sclera of the eye also is a clue to this condition. Unfortunately, because of the unusual nature of the fractures appearing in a baby who cannot yet move, some parents have been falsely accused of child abuse before osteogenesis imperfecta was diagnosed in the child.

Doctors confirm the diagnosis of osteogenesis imperfecta by taking a tiny sample of the patient's skin (a biopsy), and performing tests on this sample ina laboratory. However, it takes a long time to get results from this test, and it produces falsely negative results in about 15% of all people who have obvious symptoms of osteogenesis imperfecta.

There is no cure for osteogenesis imperfecta. Most treatments are aimed at repairing the fractures and bone deformities which the condition causes. Splints, casts, and braces are all used. When repeated fractures or bowed bones interfere with a child's ability to walk, surgeons may implant a metal rod in the bone.

Other treatments include hearing aids and early capping of teeth. Some patients need to use a walker or wheelchair. Pain may be treated with a variety ofmedications. Swimming is a good form of exercise for someone with osteogenesis imperfecta, because it increases muscle and joint strength without puttingtoo much strain on bones and joints.

Acupuncture, hypnosis, relaxation training, visual imagery, and biofeedback have all been used to try to decrease the pain of fractures.

There is no known way to prevent osteogenesis imperfecta, but adults with thecondition should have genetic counseling to understand the chance of passingit to their offspring.

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