Osteogenesis imperfecta (OI) is a genetic disorder characterized by fragile bones that break easily, often with little or no trauma. Multiple fractures can lead to permanent bone deformities, bowed bones, and bone pain. Frequently, scoliosis (spine curvature) and short stature are present. Other symptoms include muscle weakness, poor dentition and tooth loss, hearing loss, fatigue, easy bruising, and joint laxity. Many subjects with OI have a characteristic blue tint to the whites of their eyes (blue sclerae). There is a wide range of severity, from severe, lethal forms that may be picked up on prenatal ultrasound, or are noted at birth, to infantile forms the are recognized during the first year of life, to even milder forms that present with only some of the signs and symptoms later in childhood. Therefore, many patients with OI live well into adulthood and have almost normal lives.
The most frequent causes of OI are changes (mutations) in the two genes that make Type I collagen, COL1A1 or COL1A2. The collagen molecules they code for are arranged to form the structural scaffolding of bones. These mutations are dominant because they can cause the disease when only one of the two parental genes (mother’s or father’s) has a disease-causing change (dominant inheritance) leading to OI in the child if passed on from the parent. However, new changes (mutations) can also occur that were not found in either parent. About 15% of OI disorders happen only when both copies of the genes passed on by the parents carry changes that cause disease (recessive inheritance). This last group of OI disorders is caused by changes in genes that make proteins needed to transport and process the collagen molecules before they form the fibers that make up the bone scaffold in the skeleton.
A diagnosis of OI is typically based on the clinical features noted above. However, a genetic test will help confirm the diagnosis when the clinical features are not obvious or are uncertain. Genetic tests are now widely available, they are accurate and have become easier to afford. Knowing about the genetic causes of OI also helps with family planning, and in some cases, helps physicians determine the best therapy.
Drugs used for osteoporosis, such as bisphosphonates and more recently, teriparatide, are used for improving bone mass and reducing fractures in some children with OI. However, there are no FDA-approved medications for treating adults with OI, although new products are currently under study in clinical trials. Therefore, management of OI in adults requires careful clinical evaluation and an experienced physician.
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