Osteogenesis imperfecta- type 1
Overview
An inherited connective tissue disorder featuring bone fragility and blue sclerae (blue whites of the eyes). This is the classic form of "brittle bone disease." Osteogenesis imperfecta type 1 is an autosomal dominant trait. (One copy of the mutant gene is enough to cause the disease in males and females in successive generations.)
Symptoms
* Most common and mildest type of OI. * Bones predisposed to fracture. Most fractures occur before puberty. * Normal or near-normal stature. * Loose joints and muscle weakness. * Sclera (whites of the eyes) usually have a blue, purple, or gray tint. * Triangular face. * Tendency toward spinal curvature. * Bone deformity absent or minimal. * Brittle teeth possible. * Hearing loss possible, often beginning in early 20s or 30s. * Collagen structure is normal, but the amount is less than normal.
Causes
Mutations in the COL1A1 and COL1A2 genes cause osteogenesis imperfecta, type I. The proteins made by the 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). Most mutations in the COL1A1 gene reduce the amount of collagen that is produced, which weakens connective tissue. Less commonly, mutations alter the protein made by COL1A1 or COL1A2. These changes in collagen particularly affect the bones, causing the signs and symptoms of type I osteogenesis imperfecta.
Prognosis
The prognosis for an individual with OI varies greatly depending on the number and severity of symptoms. Respiratory failure is the most frequent cause of death for people with OI, followed by accidental trauma. Despite numerous fractures, restricted activity, and short stature, most adults and children with OI lead productive and successful lives. They attend school, develop friendships and other relationships, have careers, raise families, participate in sports and other recreational activities, and are active members of their communities.
Treatment
There is not yet a cure for OI. Treatment is directed toward preventing or controlling the symptoms, maximizing independent mobility, and developing optimal bone mass and muscle strength. Care of fractures, extensive surgical and dental procedures, and physical therapy are often recommended for people with OI. Use of wheelchairs, braces, and other mobility aids is common, particularly (although not exclusively) among people with more severe types of OI. A surgical procedure called "rodding" is frequently considered for people with OI. This treatment involves inserting metal rods through the length of the long bones to strengthen them. The treatment also prevents and/or corrects deformities. For more information, see the OI Foundation's fact sheet on "Rodding Surgery." Several medications and other treatments are being explored for their potential use to treat OI. These include growth hormone treatment, treatment with intravenous and oral drugs called bisphosphonates, an injected drug called teriparatide (for adults only), and gene therapies. It is not clear if people with recessive OI will respond in the same manner as people with dominant OI to these treatments. The OI Foundation can provide current information on research studies and experimental treatments for OI, as well as information to help individuals decide whether to participate in clinical trials. People with OI are encouraged to exercise as much as possible to promote muscle and bone strength, which can help prevent fractures. Swimming and water therapy are common exercise choices for people with OI, as water allows independent movement with little risk of fracture. For those who are able, walking (with or without mobility aids) is excellent exercise. People with OI should consult their physician and/or physical therapist to discuss appropriate and safe exercise. Children and adults with OI will also benefit from maintaining a healthy weight, eating a nutritious diet, and avoiding activities such as smoking, excessive alcohol and caffeine consumption, and taking steroid medications - all of which may deplete bone and exacerbate bone fragility. For more information on nutrition, see the OI Foundation fact sheet titled "Nutrition."