Understanding Osteogenesis Imperfecta
Osteogenesis imperfecta (OI) is a genetic disorder in which the bones are fragile due to defective collagen. Collagen is an important protein found in the body's connective tissues, such as bone and cartilage. In people with OI, either the quantity or the quality of collagen is abnormal, resulting in bones that are less dense and break easily.
At least four types of OI have been identified. Type I is the most common form of OI. People with this type of the disease tend to fracture easily and exhibit other features, such as blue sclera, hearing loss, a triangular face, spinal curvature, and dental problems. Type II OI, though less common, is a very severe form of the disease. Newborns with Type II often fracture before birth and usually die shortly after birth. Individuals with Type III OI tend to be very small in stature, experience hearing loss at a young age, and have a barrel-shaped rib cage, while those with Type IV tend to fracture easily and often have spinal curvature and significant dental problems.
The Osteoporosis Connection
While the traits of each type of osteogenesis imperfecta can vary greatly from person to person, consistent among all types of OI is the tendency for patients to develop low bone density at some point in their lives. For this reason, osteoporosis is an almost universal consequence of osteogenesis imperfecta. The goal of osteoporosis therapy in patients with OI involves two main concerns: increasing bone density at every age and minimizing bone loss that occurs as a result of aging. Generally, the strategies for prevention and treatment of osteoporosis among patients with OI are the same as those strategies for the rest of the population.
Minimizing Bone Loss in OI Patients
Immobilization is a critical risk factor for the development of osteoporosis in anyone. However, immobility may be virtually unavoidable for those with serious skeletal deformities or recurrent fractures. When possible, however, activities such as isometric exercise, weight lifting, standing, and walking can help reduce bone loss in people with OI.
Adequate calcium intake is another important factor for bone health. However, urine calcium excretion should be measured before substantially increasing dietary calcium, since urinary calcium excretion may be increased in some patients with OI. Eliminating other risk factors for osteoporosis, such as smoking, excessive alcohol, and prolonged use of certain bone-wasting medications, should also be considered.
Though published data are limited, various therapeutic agents continue to be investigated for their ability to minimize bone loss in people with OI at all ages. Agents currently under investigation include calcium supplements, fluoride, growth hormone, and bisphosphonates such as alendronate and pamidronate. Pamidronate has been associated with significant increases in bone density among children with OI and among adults with Type I OI.
OI and Menopause
Given the low bone density found in many patients with osteogenesis imperfecta, many women with OI are concerned about the effects of ovarian estrogen loss after menopause. It has been reported that women with OI have an increased fracture rate after menopause, although it is not clear whether the increased rate is due to aging, a lack of estrogen, or both. Despite a lack of research in this area, it is generally recommended that all postmenopausal women with osteogenesis imperfecta consider estrogen replacement therapy.
The Osteoporosis Diagnosis
Bone density measurements are often recommended for patients with OI. The three sites that are commonly measured include the spine, wrist, and hip. Unfor-tunately, several factors can interfere with a bone density reading in individuals with OI, such as significant curvature of the spine, past vertebral fractures, or the presence of metal rodding in the wrist or hip. Also, some bone density techniques (such as dual energy absorptiometry and dual energy radioabsorptiometry) may not produce accurate readings on short-statured individuals. In fact, short individuals with normal bone density may be diagnosed with low bone density by these tests. Serial measurements with such techniques can be useful, however, in evaluating changes in bone density in people with OI.
If you would like more information about osteoporosis, its diagnosis and treatment, contact the Osteoporosis and Related Bone Diseases~National Resource Center at (800) 624-BONE.
This information is reprinted from ORBD~NRC News You Can Use, "Osteoporosis in Osteogenesis Imperfecta,"Osteoporosis and Related Bone Diseases~National Resource Center, Vol. III, No. 9, July 14, 1997.
This information is brought to you by the
NIH Osteoporosis and Related Bone Diseases~National Resource Center (ORBD~NRC)
and the Osteogenesis Imperfecta Foundation
National Institutes of Health
Osteoporosis and Related Bone Diseases
National Resource Center
1232 22nd St., NW
Washington, DC 20037-1292
Tel: 800/624-BONE or 202/223-0344
Fax: 202/293-2356, TYY: 202/466-4315
The National Resource Center is supported by the National Institute of Arthritis and Musculoskeletal and Skin Diseases with contributions from the National Institute of Child Health and Human Development, National Institute of Dental and Craniofacial Research, National Institute of Environmental Health Sciences, NIH Office of Research on Women's Health, Office of Women's Health, PHS, and the National Institute on Aging. The Resource Center is operated by the National Osteoporosis Foundation, in collaboration with the Paget Foundation and the Osteogenesis Imperfecta Foundation.