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Osteogenesis imperfecta (OI) is a group of genetic disorders that mainly affect the bones. The term "osteogenesis imperfecta" means imperfect bone formation. People with this condition have bones that are brittle and easily broken. Multiple fractures are common, and in severe cases, can occur even before birth.
There are several types of osteogenesis imperfecta. The types can be distinguished by their signs and symptoms, although their characteristic features overlap. Increasingly, genetic factors are also used to define the different forms of this condition and have led researchers to propose several new types.
Type I osteogenesis imperfecta, the mildest form of the condition, is characterized by bone fractures during childhood and adolescence that often result from minor trauma. Fractures occur less frequently in adulthood. People with this form of the condition typically have a blue or grey tint to the part of the eye that is usually white (the sclera), and may develop hearing loss in adulthood. Affected individuals are usually of normal or near normal height.
Osteogenesis imperfecta type II is the most severe form of the disorder. Infants with type II have bones that appear bent or crumpled and may fracture before birth. The chest is narrow, with a very small rib cage and underdeveloped lungs. Affected infants have short, bowed arms and legs; dark blue sclerae; hips that turn outward; and unusually soft and thin skull (calvarial) bones. Most infants with type II are stillborn or die shortly after birth, usually from respiratory failure.
People with type III osteogenesis imperfecta have very fragile bones that may begin to fracture before birth. In some cases, rib fractures can cause life-threatening problems with breathing. Bone abnormalities tend to worsen over time and often interfere with mobility. People with this form of the disorder have very short stature; their adult height may be less than 3 feet. Type III osteogenesis imperfecta is also associated with blue sclerae that lighten with age, hearing loss beginning in adolescence, and a disorder of tooth development called dentinogenesis imperfecta.
Osteogenesis imperfecta type IV is a moderate form of the disorder. About 25 percent of affected individuals are born with bone fractures; others may not have any broken bones until later in childhood or adulthood. Although the sclerae may have a bluish tint in infancy, adults with this form of the condition usually have white sclerae. Additional features of type IV osteogenesis imperfecta can include mild short stature, hearing loss, and dentinogenesis imperfecta.
Researchers have proposed several additional types of osteogenesis imperfecta (types V, VI, VII, and VIII) based on the characteristic signs and symptoms and, in some cases, their genetic cause. Some of these new types are very similar to existing forms of osteogenesis imperfecta.
This condition affects an estimated 6 to 7 per 100,000 people worldwide. Types I and IV are the most common forms of osteogenesis imperfecta, affecting 4 to 5 per 100,000 people. Types II and III are rarer, with an estimated incidence of 1 to 2 per 100,000 people.
Mutations in the COL1A1, COL1A2, CRTAP, and LEPRE1 genes cause osteogenesis imperfecta.
Mutations in the COL1A1 and COL1A2 genes are responsible for about 90 percent of all cases of osteogenesis imperfecta. These genes provide instructions for making proteins that are used to assemble type I collagen, which is the most abundant protein in bone, skin, and other connective tissues that provide structure and strength to the body.
Most of the mutations that cause osteogenesis imperfecta type I occur in the COL1A1 gene. These mutations reduce the amount of type I collagen produced in the body, which causes bones to be brittle and fracture easily. The mutations responsible for osteogenesis imperfecta types II, III, and IV can occur in the COL1A1 or COL1A2 gene. These mutations typically alter the structure of type I collagen molecules. A defect in the structure of type I collagen weakens connective tissues, particularly bone, resulting in the characteristic features of osteogenesis imperfecta.
Mutations in the CRTAP and LEPRE1 genes are responsible for rare, often severe cases of osteogenesis imperfecta. The proteins produced from these genes work together to process collagen into its mature form. Mutations in either gene disrupt the normal folding, assembly, and secretion of collagen molecules. These defects weaken connective tissues, leading to severe bone abnormalities and problems with growth.
In cases of osteogenesis imperfecta without identified mutations in the COL1A1, COL1A2, CRTAP, or LEPRE1 gene, the cause of the disorder is unknown. Researchers are working to identify additional genes that are associated with this condition.
Most cases of osteogenesis imperfecta have an autosomal dominant pattern of inheritance, which means one copy of the altered gene in each cell is sufficient to cause the condition. Many people with type I or type IV osteogenesis imperfecta inherit a mutation from a parent who has the disorder. Almost all infants with more severe forms of osteogenesis imperfecta (type II and type III) have no history of the condition in their family. In these infants, the condition is caused by new (sporadic) mutations in the COL1A1 or COL1A2 gene. The disorder is not passed on to the next generation because most affected individuals do not live long enough to have children.
Less commonly, osteogenesis imperfecta has an autosomal recessive pattern of inheritance. Autosomal recessive inheritance means two copies of the gene in each cell are altered. The parents of a child with an autosomal recessive disorder typically are not affected, but each carry one copy of the altered gene. Some cases of osteogenesis imperfecta type III are autosomal recessive; these cases usually result from mutations in genes other than COL1A1 and COL1A2. Rare cases of osteogenesis imperfecta caused by mutations in the CRTAP or LEPRE1 gene also have an autosomal recessive pattern of inheritance.
'''Osteogenesis imperfecta''' ('''OI'''), commonly known as '''brittle bone disease''', is a group of genetic disorder bone disorders. People with OI do not produce enough good quality collagen to produce healthy, strong bones. Collagen is an important protein and without a good enough supply the bones are weak and break very easily. As a genetic disorder, OI is a autosomal dominant defect. Most people with OI receive it from a parent but it can also be an individual (''de novo'' or "sporadic") mutation.
Osteogenesis Imperfecta: The Links to Nutrition - Reviews the possible role of nutrition in this disorder. Questions whether it is solely a genetic condition.
Osteogenesis Imperfecta Information - Resources gathered by the mother of a child with the disease. Includes a personal page about her son Jojo, his disease, treatment, and progress.
The Osteogenesis Imperfecta Mailing List - For the discussion of any issues relating to OI. Open to both professionals and families.
Brittle Bone Society - The UK charity providing support for people with osteogenesis imperfecta.
Osteogenesis imperfecta hub - Links to overviews, clinical trials, images, research articles and abstracts for osteogenesis imperfecta.
Osteogenesis Imperfecta Federation Europe - Information on Osteogenesis Imperfecta around Europe
Osteogenesis Imperfecta - Fact sheets from the National Institutes of Health.
Osteogenesis Imperfecta - Overview from the University of Maryland.
Osteogenesis Imperfecta - Article from eMedicine.
Osteogenesis Imperfecta Foundation - Supports and encourages medical research and disseminates information to patients, their families, and medical professionals