Osteogenesis imperfecta (OI) is the most common disease causing fractures in childhood. It also causes fractures in adults. OI is a genetic disorder usually resulting from abnormalities of the genes that control the production of a protein called collagen; which is the main protein in bone and essential for its strength. The fragility of bone in OI is due to the collagen problems; it has nothing to do with the calcium part of bone, which is what shows up on X-rays.

All of the bones are abnormally weak in a person with OI. The severity of the abnormality varies enormously -- from type 2 OI, which is usually lethal in infancy (or even before birth) to type 1 OI, which may be so mild that the diagnosis is not made, even in adulthood.

The three classic symptoms of OI includes fragile bones, early hearing loss, and whites of the eyes that appear bluish (blue sclerae). Nevertheless, not all people with OI will have blue sclerae or hearing loss. All do have fragile bones, but not all people with OI will ever break a bone.

A variety of other symptoms may be found in the various types of OI:
Bone fracture (broken bone)
More than one broken bone occurring in a single episode (multiple)
Fractures present at birth
Occuring after only minor trauma
Deformed or short extremities (such as leg deformities or arm deformities)
Deafness (conductive hearing loss may occur in adolescents and adults)
Kyphosis
Kyphoscoliosis
Short stature
Tooth abnormalities
Low nasal bridge
Pectus carinatum
Pectus excavatum
Pes planus (flat feet)
Joint laxity
Hypermobility
Easy bruising
Bowed legs.

The defect may be inherited in an autosomal dominant pattern from an affected parent. This means that a parent with a single gene for OI has a 50% chance of having a child with the disorder. Any child who inherits this gene will be affected.

The defect may be acquired by a spontaneous mutation occurring in the individual egg or sperm that formed the child. In this case, neither parent carries a gene for the disorder or is affected by it. The parents, in this case, are no more at risk than the general population for having another child with the disorder.

The defect may be acquired through a pattern of inheritance called mosaicism. This occurs when neither parent is affected, but one carries a percentage of sperm or eggs which contain the genetic defect. Therefore, though the parents are unaffected, some of their children may have the disorder and others will not. It is estimated that about 2% to 7% of unaffected parents who have had a child with OI will have another child with OI due to the phenomenon of mosaicism.