Osteogenesis imperfecta
Osteogenesis imperfecta is a congenital (present from birth)
condition of abnormal fragility of the bones.
Information about Osteogenesis imperfecta
This bone disorder is usually present at birth as an inherited
disease. Osteogenesis imperfecta (OI) is classified into four major types (and further
subtypes).
All four types of OI are caused by defects in the amount or structure of Type 1
collagen, an important part of the bone matrix. The collagen problem usually results from
a dominant genetic defect. This defect may be acquired by several different mechanisms:
- The defect may be inherited in an autosomal dominant pattern from an affected parent.
This means that an affected parent, who carries a single gene for the disorder, has a 50%
chance of having children with the disorder. Any child who inherits this gene will be
affected.
- The defect may be acquired by a spontaneous mutation occurring in the individual egg or
sperm that formed the child. In this case, neither parent carries a gene for the disorder
or is affected by it. The parents, in this case, are no more at risk than the general
population for having another child with the disorder.
- The defect may be acquired through a pattern of inheritance called mosaicism. This
occurs when neither parent is affected, but one carries a percentage of sperm or eggs
which contain the genetic defect. Therefore, though the parents are unaffected, some of
their children may have the disorder and others will not. It is estimated that about 2% to
7% of unaffected parents who have had a child with OI will have another child with OI due
to the phenomenon of mosaicism.
Symptoms Return to top
When people have OI, all of their bones are abnormally weak. The severity of the
abnormality varies enormously -- from Type II OI, which is usually lethal in infancy (or
even before birth) to Type I OI, which may be so mild that the diagnosis is not made, even
in adulthood.
The three classic symptoms of OI includes fragile bones, early hearing loss, and whites
of the eyes that appear bluish (blue sclerae). Nevertheless, not all people with OI will
have blue sclerae or hearing loss. All do have fragile bones, but not all people with OI
actually ever break a bone.
A variety of other symptoms may be found in the various types of OI:
- bone fracture (broken bone)
- more than one broken bone occurring in a single episode (multiple)
- present at birth
- occuring after only minor trauma
- a minority of people with OI never break a bone
- deformed or short extremities (such as leg deformities or arm deformities)
- deafness (conductive hearing loss may occur in adolescents and adults)
- kyphosis
- kyphoscoliosis
- short stature
- tooth abnormalities
- low nasal bridge
- pectus carinatum
- pectus excavatum
- pes planus (flat feet)
- joint laxity
- hypermobility
- easy bruising
- bowed legs
Diagnosis of Osteogenesis imperfecta
Diagnosis is usually suspected when a baby has bone fractures after having suffered no
apparent injury. Sometimes the bluish sclera serves as a diagnostic clue. Unfortunately,
because of the unusual nature of the fractures occurring in a baby who cannot yet move,
some parents have been accused of child abuse before the actual diagnosis of osteogenesis
imperfecta was reached.
The diagnosis is confirmed by taking a tiny sample of the patient's skin (a biopsy),
and performing tests on this sample in a laboratory. The collagen fibers in the skin are
studied for evidence of abnormalities. These tests are highly specialized, and the results
may not be available for as long as six months. Furthermore, this type of testing will
yield a falsely negative result in about 15% of all people who have obvious symptoms of
OI. Currently, this is the only test available to diagnose OI; genetic testing is not yet
available.
Treatment of Osteogenesis imperfecta
There are no treatments available to cure OI, nor to prevent most of its complications.
Most treatments are aimed at treating the fractures and bone deformities which OI causes.
Splints, casts, and braces are all used. Rodding refers to a surgical procedure in which a
metal rod is implanted within a bone (usually the long bones of the thigh and leg). This
is done when bowing or repeated fractures of these bones has interfered with a child's
ability to begin to walk.
Other treatments include hearing aids and early capping of teeth. Patients may require
the use of a walker or wheelchair. Pain may be treated with a variety of medications.
Swimming is a form of exercise which puts a minimal amount of strain on muscles, joints,
and bones. It is helpful for increasing muscle and, therefore, joint strength.
Prognosis of Osteogenesis imperfecta
Fifty percent of all babies with OI Type II are born dead. The rest of these babies
usually die within a very short time of being born. The prognosis for people with other
types of OI is quite variable, depending on the severity of the disorder and the number
and severity of the fractures and bony deformities.
Prevention of Osteogenesis imperfecta
There is no known way to prevent OI, although adults with OI should be carefully
counseled regarding the chance of their offspring being born with the disease. In the
dominant form of OI, a child who has one parent with the disease has a 50% chance of also
having the disease. In the recessive form of OI, a child who has two parents with the
disease has a 25% chance of having the disease, a 25% chance of being completely
unaffected, and a 50% chance of being a carrier. A carrier is someone who does not have
the disease itself, but "carries" the defective gene, and thus can pass it on to
future offspring. A child who has only one parent with the recessive form of OI has no
chance of actually having the disease, but a 50% chance of being a carrier. |
