Definition

Osteogenesis Imperfecta (OI) is a genetic disorder characterized by bones that break easily, often from little or no apparent cause. There are at least four distinct forms of the disorder, representing extreme variation in severity from one individual to another. For example, a person may have as few as ten or as many as several hundred fractures in a lifetime.

Prevalence

While the number of persons affected with OI in the United States is unknown, the best estimate suggests a minimum of 20,000 and possibly as many as 50,000.

Diagnosis

Most forms of OI are caused by imperfectly formed bone collagen, the result of a genetic defect. Collagen is the major protein of the body's connective tissue and can be likened to the framework around which a building is constructed. In OI, a person has either less collagen or a poorer quality of collagen.

Collagen testing, which is done through a skin biopsy, is used to determine the amount of collagen present and its structure. While these studies identify the vast majority of people who have OI, approximately 15% of individuals with obvious features of OI do not demonstrate a collagen abnormality sufficient enough to be detected by the testing. Because of the complexity of the test, as well as the limited number of laboratories that are qualified to do the testing, it may take 3 to 6 months before test results are known.

Clinical Features

The characteristic features of OI vary greatly from person to person and not all characteristics are evident in each case; however, the general features of OI, which vary in characteristics as well as severity, are:

Type I OI:

• Most common
• Bones fracture easily
• Can usually be traced through the family
• Near normal stature or slightly shorter
• Blue sclera
• Dental problems
• Hearing loss beginning in the early twenties and thirties
• Most fractures occur before puberty; occasionally women will have fractures after menopause
• Triangular face
• Tendency toward spinal curvatures

Type II OI:

• Newborns severely affected; frequently lethal
• Usually resulting from a new gene mutation
• Very small stature with extremely small chest and under developed lungs

Type III OI:

• Tend to be isolated family incidents
• Very small in stature - some only three feet tall
• Fractures at birth very common
• X-ray may reveal healing of in utero fractures
• Severe early hearing loss
• Loose joints and poor muscle development in arms and legs
• Barrel-shaped rib cage

Type IV OI:

• Can frequently be traced through the family
• Bones fracture easily - most before puberty
• Normal or near normal colored sclera
• Problems with teeth - more than type 1
• Spinal curvatures
• Loose joints

Inheritance Factors

OI can be dominantly or recessively inherited and can also occur as a mutation. Therefore, individuals with OI and parents of children with OI are strongly encouraged to seek genetic counseling to determine the likelihood of OI recurring in their families.

Treatment

At present there is no cure for OI. Treatment is directed toward preventing or correcting the symptoms. Care of fractures, extensive surgical and dental procedures, and physical therapy are often recommended for persons with OI. Wheelchairs, braces, and other custom-made equipment are often necessary. Individuals are encouraged to seek out medical centers where all aspects of OI, including biochemical, orthopedic, dental, and hearing problems, can be treated.

An orthopedic procedure called "rodding" is frequently considered for individuals with OI. This treatment involves inserting metal rods through the length of the long bones to strengthen them and prevent deformities.

Prognosis

The prognosis for an individual with OI varies greatly depending on the number of symptoms as well as the severity of the symptoms. Despite numerous fractures, restricted activity, and short stature, many adults and children with OI lead productive and happy lives.