Osteogenesis imperfecta
medical conditions

Osteogenesis imperfecta

Explore the available health information, treatment context, and integrative evidence for Osteogenesis imperfecta.

Background
  • Osteogenesis imperfecta or OI (meaning "imperfect bone formation") is a group of inherited disorders that affects the bones and connective tissues. People with this condition are born with a reduced bone mass, which results in fragile bones that break easily.
  • There are at least eight forms of OI that are distinguished by the severity of the symptoms. Milder cases sometimes go unnoticed until adulthood and may involve only a few bone fractures. In severe cases, the bones are extremely fragile and may fracture frequently, even with no or little apparent cause.
  • Collagen is the major protein of the body's connective tissue. It is part of the framework around which bones are formed. Most types of OI (about 85%) are caused by a mutation in the gene that produces type 1 collagen. There are many different mutations that can affect this gene. The severity of OI depends on the specific gene mutation, which can cause the body to make either too little or low-quality type 1 collagen. It is estimated that 20,000-50,000 people in the United States have OI.
  • People with OI may have blue sclera, meaning that the whites of the eyes have a blue tint. They may also have a short stature, hearing loss, restricted physical abilities, breathing problems, and weak teeth. Despite these symptoms, most people with OI live relatively normal lives.
Risk Factors and Causes
  • Because osteogenesis imperfecta (OI) is inherited, the only known risk factor is a family history of the disorder. Evidence that OI preferentially affects any particular gender, ethnicity, or age group, is lacking in the available literature.

  • General: Osteogenesis imperfecta (OI) is usually caused by genetic defects that affect the body's ability to make strong bones. In the majority of OI cases, a person has too little type I collagen or type I collagen that is of poor quality due to a mutation in one of the genes that encode for the protein that makes type I collagen.
  • Mutations: Mutations in the COL1A1 and COL1A2 genes are responsible for most cases of OI. These genes provide instructions for making proteins that are used to assemble type I collagen. This type of collagen is the most abundant protein in bone, skin, and other connective tissues. These mutations are responsible for most cases of types II, III, and IV OI. These genetic changes reduce the amount of type I collagen produced in the body, which causes bones to be brittle and to break easily.
  • Mutations in the CRTAP and LEPRE1 genes are responsible for rare, often severe cases of OI. Cases caused by CRTAP mutations are classified as type VII. Cases caused by LEPRE1 mutations are classified as type VIII. The proteins produced from these genes work together to process collagen into its mature form. These mutations weaken connective tissues, leading to severe bone abnormalities and problems with growth.
  • In some individuals, no mutations are detectable. In cases of OI without identified mutations in the COL1A1, COL1A2, CRTAP, or LEPRE1 genes, the cause of the disorder is unknown. These cases include types V and VI. Scientists are working to identify additional genes that may be responsible for these conditions. In other cases of OI, there are mutations in a cartilage-related protein called 3-prolyl-hydroxylase.
  • Autosomal dominant inheritance: Most cases of OI are caused by an autosomal dominant genetic defect. Each gene has two variations, called alleles. One allele is inherited from each parent. For diseases that are inherited as autosomal dominant traits, only one mutated allele is necessary for the child to have OI. A parent with this type of OI has a 50% chance of passing on the disorder to each child. Types of OI than can be inherited in an autosomal dominant manner are types I, II, III, and IV.
  • Autosomal recessive inheritance: Approximately 10% to 15% of cases of OI are the result of an autosomal recessive mutation. In this case, an affected child receives a copy of the mutated gene from both parents. Most often, parents of a child with an autosomal recessive disorder are not affected but possess, or are carriers of, one copy of the mutated gene. If both parents are carriers, there is a 25% chance of having an affected child with each pregnancy. Types of OI that can be inherited in an autosomal recessive manner include types VII and VIII. Some unusual cases of type III are autosomal recessive.
  • Random occurrence: While most cases of OI are inherited from a parent, some are the result of spontaneous or new genetic mutations that occur early in fetal development. These cases tend to be severe, and occur within individuals with no family history of the disorder. The collagen-encoding genes that are mutated in these cases are usually COL1A1 or COL1A2.
Signs and Symptoms
  • Symptoms of osteogenesis imperfecta (OI) vary greatly from person to person, even among people with the same type of the disorder. All affected individuals have weak bones that break easily. They are usually below average height.
  • Other symptoms may include a blue tint to the whites of the eyes (blue sclera), early hearing loss, loose joints, bowed arms and legs, scoliosis (curved spine), lung problems, flat feet, and poorly developed teeth. These symptoms are caused by the defective formation of bone and connective tissue.
  • The most severe forms of OI, particularly type II, can include an abnormally small, fragile rib cage and underdeveloped lungs. Affected infants may die from breathing problems.
Diagnosis
  • General: It may be possible to diagnose osteogenesis imperfecta (OI) based solely on symptoms. OI is usually suspected in children whose bones break with very little force. A physical examination may show that the whites of the eyes (sclera) have a blue tint.
  • Collagen analysis: Collagen analysis from a skin sample may confirm a clinical diagnosis. The collagen biopsy test looks for mutations in the COL1A1, COL1A2, CRTAP, and LEPRE1 genes.
  • Genetic tests: DNA sequencing from a blood sample may confirm a clinical diagnosis. A positive type I collagen genetic test confirms the diagnosis of autosomal dominant OI, but a negative result does not rule out OI. When a type I collagen mutation is not found, other DNA tests are used to check for other types of OI. Due to the fact that so many different mutations can cause OI and that many mutations have not been identified, some forms cannot be diagnosed with a genetic test.
  • Prenatal diagnosis: Severe forms can sometimes be diagnosed prenatally (or while the fetus develops in the womb). If there is a family history of OI, chorionic villus sampling or amniocentesis may be done during pregnancy to determine if the baby has mutations that could cause the condition. In some cases, an ultrasound can identify bone abnormalities in an unborn baby at 14-18 weeks.
Complications
  • Complications are based on the type of osteogenesis imperfecta (OI) present. They are often directly related to problems with weak bones and improperly formed collagen. Casting of broken bones should be limited since further bone loss may occur when a part of the body is not used for a period of time. This is called atrophy or a wasting away of a part of the body.
  • Hearing loss is common in type I and type III because the bones of the ear that are necessary for hearing become fragile. Heart failure may occur in type II, possibly due to not enough oxygen getting to the heart. Other complications may include respiratory problems and pneumonias due to chest wall deformities, spinal cord or brain stem problems, and respiratory failure.
Treatment
  • General: There is no known cure for osteogenesis imperfecta (OI). Treatment aims to prevent or control the symptoms, maximize mobility, and maintain or increase bone mass and muscle strength. Casting of broken bones should be limited since further bone loss may occur when a part of the body is not used for a period of time. This is called atrophy or a wasting away of a part of the body. A social worker or psychologist can help young people adapt to life with OI.
  • Activity: Swimming and water therapy may be helpful to patients with OI. Walking, if possible, is also recommended. People with OI should consult with their physician and/or physical therapist to discuss appropriate and safe exercise.
  • Assistive devices: The use of wheelchairs, braces, and other mobility aids is common among people with more severe types of OI.
  • Diet: OI patients also benefit from maintaining a healthy weight and eating a nutritious diet. OI patients should avoid smoking and excessive alcohol and caffeine consumption, which can decrease bone strength.
  • Drugs: Bisphosphonates are the best drug therapy available to treat OI. These are drugs that have been used to treat osteoporosis and have been proven to be very valuable in the treatment of OI symptoms, particularly in children. They work by inhibiting the breakdown of bone and its resorption by the body. Benefits of bisphosphonate treatment include decreased pain, lower fracture incidence, better mobility, and increased strength and bone density. Among the various bisphosphonates, pamidronate (brand name Aredia®) given intravenously (IV) has been shown to reduce bone pain and increase bone mass and density. However, the optimal treatment dose and the long-term effects of pamidronate treatment are not known. Treatment with bisphosphonates during growth may be reserved for patients who have severe or life-threatening symptoms.
  • Growth hormone treatment and an injected drug called teriparatide, are being evaluated. These treatments can stimulate bone growth. People with OI should avoid taking steroid medications, which can decrease bone strength.
  • Gene-based therapies: Gene-based therapies for OI patients are currently being studied. A new approach has been developed to replace mutated genes using stem cells and DNA. It is experimental and limited by the number of gene mutations.
  • Surgery:
    Reconstructive surgery may be needed to correct deformities such as bowed legs or spinal problems. A surgical procedure called "rodding" is frequently used. Rodding involves inserting metal rods through the length of the long bones to strengthen them, prevent and correct deformities, and to reduce the risk of fracture.
Prevention
  • Genetic counseling is recommended for couples considering pregnancy if there is a personal or family history of this condition. Genetic counselors can help people with OI and their family members further understand OI genetics and assist in prenatal diagnosis.
References
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    View Abstract
  2. GeneTests website. . Accessed April 6, 2008.
  3. Genetics home reference. . Accessed April 6, 2008.
  4. Glorieux FH. Treatment of osteogenesis imperfecta: who, why, what? Horm Res. 2007;68 Suppl 5:8-11.
    View Abstract
  5. Martin E, Shapiro JR. Osteogenesis imperfecta:epidemiology and pathophysiology. Curr Osteoporos Rep. 2007 Sep;5(3):91-7.
    View Abstract
  6. National Institute of Arthritis and Musculoskeletal and Skin Diseases. . Accessed April 6, 2008.
  7. Natural Standard: The Authority on Integrative Medicine. Copyright © 2008. . Accessed April 6, 2008.
  8. Osteogenesis Imperfecta Foundation. . Accessed April 6, 2008.
  9. Rauch F, Glorieux FH. Osteogenesis imperfecta. Lancet. 2004 Apr 24;363(9418):1377-85.
    View Abstract
  10. Rauch F, Glorieux FH. Treatment of children with osteogenesis imperfecta. Curr Osteoporos Rep. 2006 Dec;4(4):159-64.
    View Abstract