Osteogenesis Imperfecta, Type III

What is osteogenesis imperfecta, type III?

Osteogenesis imperfecta is a group of inherited disorders that mainly affect the bones, causing them to be fragile and easily broken. Type III is a severe form of the disorder; its signs and symptoms fall between the very severe osteogenesis imperfecta type II and the milder osteogenesis imperfecta type I.

Osteogenesis imperfecta, type III is a subtype of osteogenesis imperfecta.

Infants with this form of osteogenesis imperfecta have soft, fragile bones that fracture easily. Broken bones may occur even before birth. People with the disorder are much shorter than average (adult height ranges from just under 3 feet to about 4 feet) because the condition prevents bones from growing normally. Spinal curvature (scoliosis) and bone abnormalities often become progressively worse during childhood, but tend to stabilize during adolescence. These complications may shorten a person's lifespan by affecting heart and lung function. Other signs and symptoms include a light blue tint to the part of the eyeball that is usually white (the sclera), brittle and discoloured teeth, loose joints, and, in some cases, hearing loss.

How common is osteogenesis imperfecta, type III?

This form of osteogenesis imperfecta probably has a birth frequency of about 1 in 60,000.

What genes are related to osteogenesis imperfecta, type III?

Mutations in the COL1A1 and COL1A2 genes cause osteogenesis imperfecta, type III.

The proteins made by COL1A1 and COL1A2 genes are used to assemble larger molecules called type I collagen, the major protein in bones. Collagens provide structure and strength to connective tissue (the type of tissue that forms a supportive framework for the body's muscles, ligaments, skin, and bones). Mutations in either gene prevent collagen molecules from being assembled correctly. This defect weakens connective tissue, particularly in bone, which causes the bone abnormalities seen in this condition.

In some instances, this condition may result from mutations in other genes that have not yet been identified.

How do people inherit osteogenesis imperfecta, type III?

This disorder can be inherited in either an autosomal dominant or an autosomal recessive pattern. Most cases in North America and Europe are autosomal dominant, which means one copy of the altered gene is sufficient to cause the disorder. Rare cases are autosomal recessive, which means two copies of the gene must be altered to cause the condition. The autosomal recessive form of type III osteogenesis imperfecta is much more frequent in eastern Mediterranean and black South African populations, and usually results from mutations in genes other than COL1A1 and COL1A2.

What other names do people use for osteogenesis imperfecta, type III?

  • OI, type 3
  • Osteogenesis imperfecta, progressively deforming, with normal sclerae
  • Progressively deforming osteogenesis imperfecta with normal sclerae

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