Brittle bone disease is a congenital disorder that results in fragile bones that break easily. When it occurs, it is present at birth, but only in babies who have a family history of the disease.
Your doctor may refer to the disease as osteogenesis imperfecta (OI), which means "imperfectly formed bone." Brittle bone disease can range from mild to severe. Most cases are mild, resulting in few bone fractures. However, the severe forms of the disease can cause hearing loss, respiratory or heart failure, spinal cord and brain stem problems, and permanent deformities.
In some forms, the disease is fatal to babies either before, or shortly after birth. According to the National Human Genome Research Institute (NHGRI), approximately three people in 50,000 are born with brittle bone disease. It occurs equally among each sex and race. (NHGRI)
Brittle bone disease is caused by a genetic defect that affects the production and formation of type 1 collagen, a protein used to create bone. The defective gene is usually inherited, but in some cases the defect occurs due to a spontaneous mutation.
There are four different genes responsible for collagen production, and any combination, or all, of them can be affected. These combinations produce eight types of brittle bone disease, labeled as type 1 OI through type 8 OI. The first four types are the most common. The last four types are extremely rare and most are subtypes of type 4 OI. Details for each type include:
Type 1 OI
Type 1 OI is the mildest and most common form of brittle bone disease your baby can have. With this type, your child’s body produces normal quality collagen, but just not enough of it. This results in only mildly fragile bones. Children with type 1 OI typically experience bone fractures due to mild traumas. Such bone fractures are much less common in adults. The teeth may also be affected, resulting in dental cracks and cavities.
Type 2 OI
Type 2 OI, the most severe form of brittle bone disease, is fatal. In type 2 OI, your child’s body either produces poor-quality collagen or not enough of it. Type 2 OI can produce bone deformities. Infants born with type 2 OI may have narrowed chests, broken or misshapen ribs, and underdeveloped lungs. Babies with type 2 OI die either in the womb or shortly after birth.
Type 3 OI
Type 3 OI is a severe form of brittle bone disease that also causes bones to break easily. In Type 3 OI, your child’s body produces enough collagen, but it is of poor quality. A baby’s bones can even begin to break before birth. Bone deformities are common and may get worse as your child gets older.
Type 4 OI
Type 4 OI is the most variable form of brittle bone disease because its symptoms range from mild to severe. As with type 3 OI, the body produces enough collagen, but the quality is poor. Infants with type 4 OI are typically born with bowed legs, although the bowing tends to lessen with age.
The symptoms of brittle bone disease vary according to the type of the disease. Everyone who suffers from brittle bone disease has fragile bones to varying degrees. If you have brittle bone disease, you also may have one or more of the following symptoms:
- bone deformities
- multiple broken bones
- loose joints
- short stature
- weak teeth
- triangular-shaped face
- blue sclera (bluish color in the white of the eye)
- bowed legs and arms
- kyphosis (an abnormal outward curve of the upper spine)
- scoliosis (an abnormal lateral curve of the spine)
- early hearing loss
- respiratory problems
- heart defects
Your doctor can diagnose brittle bone disease through X-rays to view current and past broken bones and to view defects in your bones. Lab tests can analyze the structure of your child’s collagen. Your doctor may want to run a skin punch test for a biopsy. The doctor will use a sharp, hollow tube to remove a bit of tissue approximately the size of a pencil eraser.
Genetic testing can trace the source of any defective genes.
Although there is no cure for brittle bone disease, there are supportive therapies that help reduce the risk of broken bones and increase quality of life. Treatments for brittle bone disease include:
- physical and occupational therapy to increase your child’s mobility and muscle strength to help reduce risk of fractures
- bisphosphonate medications to increase bone formation
- medication to reduce any pain
- low-impact exercise to help build bone
- surgery to place rods in the bones to strengthen them
- reconstructive surgery to correct bone deformities
- mental-health counseling to help with body-image issues
Your prognosis varies depending on the type of brittle bone disease. Outlooks for the four main types of brittle bone disease are:
Type 1 OI
People with type 1 OI can live a normal lifespan with relatively few problems.
Type 2 OI
Type 2 OI is fatal. Infants with type 2 OI may die in the womb, or shortly after birth from respiratory problems.
Type 3 OI
Children with type 3 OI may have severe bone deformities and often require a wheelchair to get around. People with type 3 OI usually have shorter lifespans than anyone with type 1 or 4 OI.
Type 4 OI
Children with type 4 OI may need crutches to walk. The lifespan of people with type 4 OI is normal or close to normal.