Osteogenesis imperfecta (brittle bones) is a hereditary disease of bones and connective tissue that may cause varying degrees of skeletal fragility, thin skin, blue sclerae, poor teeth, hypermobility of joints, and progressive deafness. This disease occurs in many forms. In the rare congenital form, fractures are present at birth. This form is usually fatal within the first few days or weeks of life. In the late-appearing form, the child appears normal at birth but develops recurring fractures (mostly of the extremities) after the first year of life.
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.
Clinical severity varies, depending on the type. In type I, fractures characteristically occur from minimal trauma. The sclerae are a deep blue-black color, and the teeth may be yellow or even grayish blue from opalescent dentin. Patients with dental abnormalities are shorter and have more fractures at birth, more frequent fractures, and more severe skeletal deformities than type I patients with normal teeth.
Bowing of the lower limbs is common in this type, as is kyphosis in adults. Approximately 40% of all adults with type I have severely impaired hearing, and virtually all adults have some degree of hearing impairment by age 50. The number of fractures may spontaneously decrease in adolescence.
Type II is characterized by intrauterine fractures due to extreme bone fragility, leading to intrauterine or early infant death. Death usually results from complications of bone fragility, heart failure, pulmonary hypertension, or respiratory failure. Therapeutic intervention doesn't usually increase survival.
Type III is generally nonlethal. Fractures are usually present at birth and occur frequently in childhood; they typically lead to progressive skeletal deformity and, eventually, impaired mobility. Patients have a poor growth rate; most fall below the third percentile in height for their age. Their sclerae are usually normal or light blue, and their teeth aren't usually opalescent.
Type IV is characterized by osteoporosis, which leads to increased bone fragility. The sclerae may be light blue at birth but appear normal in adolescents and adults. Bowed limbs may be present at birth, but only 25% of patients have fractures at birth. The number of fractures may decrease spontaneously at puberty, but the majority of patients are short. A few have a skull deformity.
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.
Treatment aims to prevent deformities by traction, immobilization, or both and to aid normal development and rehabilitation. Fractures must be repaired quickly to avoid deformities. Surgical procedures such as inserting metal rods through bones can help strengthen bones and prevent deformity. The use of bisphosphonates in children with osteogenesis imperfecta is being researched, as are growth hormone and gene therapies. Other medical interventions include bone marrow transplant. Supportive measures include:
❑ checking the patient's circulatory, motor, and sensory abilities
❑ encouraging the patient to walk when possible (children with osteogenesis imperfecta develop a fear of walking)
❑ teaching preventive measures, such as avoiding contact sports or strenuous activities or wearing knee pads, helmets, or other protective devices when engaging in sports
❑ assessing for and treating scoliosis, a common complication
❑ promoting preventive dental care and repair of dental caries.
❑ Educate the family about the disorder. Teach the parents and child how to recognize fractures and how to correctly splint them. Also teach the parents how to protect the child during diapering, dressing, and other activities of daily living.
❑ Advise the parents to encourage their child to develop interests that don't require strenuous physical activity and to develop his fine motor skills. These actions will promote the child's self-esteem.
❑ Advise the parents that physical and rehabilitation therapy is beneficial. Swimming is an excellent conditioning exercise.
❑ Teach the child to assume some responsibility for precautions during physical activity to help foster his independence.
❑ Stress the importance of good nutrition to heal bones and optimize muscle strength.
❑ Refer the parents and child for genetic counseling to assess the recurrence risk.
❑ Administer analgesics, as ordered, to relieve pain from frequent fractures, a hallmark of this disease.
❑ Monitor dental and hearing needs. Stress the need for regular dental care and immunizations.
❑ Instruct the parents to provide a medical identification bracelet for the child.
Review other book chapters online related to Osteogenesis imperfecta:
Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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More About This Book:
Title: Professional Guide to Diseases (Eighth Edition) Authors: Springhouse Publisher: Lippincott Williams & Wilkins Copyright: 2005 ISBN: 1-58255-370-X 
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