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Osteogenesis Imperfecta
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. |
