Osteogenesis imperfecta- type 6
A rare form of the genetic connective tissue disorder characterized by fragile bones and light-colored eyes. There are a number of types of osteogenesis imperfecta and type 6 is considered a moderate to severe form.
* Clinically similar to Type IV in appearance and symptoms of OI. * The alkaline phosphatase (an enzyme linked to bone formation) activity level is slightly elevated in OI Type VI. This can be determined by a blood test. * Bone has a distinctive "fish-scale" appearance when viewed under the microscope. * Diagnosed by bone biopsy. * Whether this form is inherited in a dominant or recessive manner is unknown, but researchers believe the mode of inheritance is most likely recessive. * Eight people with this type of OI have been identified.
Osteogenesis imperfecta can result from autosomal dominant inheritance of a defect in the amount of Type I collagen, an important part of the bone matrix. Clinical signs may result from defective osteoblastic activity and a defect of mesenchymal collagen (embryonic connective tissue) and its derivatives (sclerae, bones, and ligaments). The reticulum fails to differentiate into mature collagen or causes abnormal collagen development, leading to immature and coarse bone formation. Cortical bone thinning also occurs. Type I, the most common form of osteogenesis imperfecta, occurs in about 1 in 30,000 live births. Both types I and IV are thought to be inherited as an autosomal dominant trait. Types II and III are believed to be inherited as an autosomal recessive trait.
Family history and characteristic features, such as blue sclerae or deafness, establish the diagnosis. Whenever possible, collagen biochemical studies of cultured skin fibroblasts should be performed. Prenatal diagnosis may be available for certain families with an identified mutation. Prenatal ultrasound performed as early as 16 weeks may show evidence of severe osteogenesis imperfecta. X-rays showing evidence of multiple old fractures and skeletal deformities and a skull X-ray showing wide sutures with small, irregularly shaped islands of bone (wormian bones) between them support the diagnosis. These findings can help differentiate osteogenesis imperfecta from child abuse or from other disorders such as juvenile idiopathic osteoporosis. In a family with a history of type II osteogenesis imperfecta, diagnostic serial ultrasound should be considered for future pregnancies to detect limb shortening, in utero fractures, and polyhydramnios.
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.
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."