Osteogenesis imperfecta (OI) is a genetic disorder characterized by bones that break easily, often from little or no apparent cause. There are at least four recognized forms of the disorder, representing a range of severities. For example, a person may have just a few or as many as several hundred fractures in a lifetime.
OI is caused by a genetic defect that affects the body’s production of collagen. Collagen is the major protein of the body’s connective tissue and can be likened to the framework around which a building is constructed. In OI, a person has either less collagen than normal, or a poorer quality of collagen than normal, leading to weak bones that fracture easily.
It is often, though not always, possible to diagnose OI based solely on clinical features. Clinical geneticists can also perform biochemical (collagen) or molecular (DNA) tests that can help confirm a diagnosis of OI in some situations. These tests generally require several weeks before results are known. Both the collagen biopsy test and DNA test are thought to detect almost 90% of all collagen type 1 mutations.
A positive collagen type 1 study confirms the diagnosis of OI, but a negative result leaves open the possibility that either a collagen type 1 mutation is present but was not detected or the patient has a form of the disorder that is not associated with collagen type 1 mutations. Therefore, a negative collagen type 1 study does not rule out OI.
The characteristic features of OI vary greatly from person to person, even among people with the same type of OI, and even within the same family, and not all characteristics are evident in each case. The general features of the four recognized types (Types I-IV) of OI, which vary in characteristics and severity.
*Taken from www.oif.org