Osteopetrosis
May 16th, 2008 Posted by: admin
A hereditary bone disorder
Osteopetrosis is a congenital disorder (a person is born with it) in which the bones are dense, brittle and break easily.
Who is affected
Deppending of the form of osteopetrosia, both children and adults can be affected. It is difficult to estimate how often the different forms of osteopetrosis occur worldwide.
Causes
The basis of the disease is that special bone cells called osteoclasts do not function normally. These osteoclasts usually break down old bone tissue as new bone tissue grows. In osteopetrosis, since the old bone tissue is not broken down, the bones in the body overgrow. In the head and spine this overgrowth puts pressure on nerves and causes neurological problems. In the bones where bone marrow usually forms, the overgrowth crowds out the bone marrow. The overgrown, dense bones are very brittle and break easily.
Forms of osteopetrosis
There are several forms of the disease, ranging from mild to severe.
- Malignant infantile osteopetrosis
This severe form begins to affect the baby even before he or she is born. Because the bones are britlle, during the birth process, the baby’s shoulder bones may break.
Malignant infantile osteopetrosis is usually apparent at birth, and during the first few months of life the infant has:
- low calcium (which can cause seizures)
- pressure on the optic nerve in the brain (leading to visual impairment or blindness)
- frequent fractures of bones.
Possible problems that may be developed during the first year of life:
- anemia (low number of red blood cells)
- thrombocytopenia (low number of platelets in the blood)
Untreated children with malignant infantile osteoporosis have difficulty surviving beyond age 10.
- Adult (benign) osteopetrosis
Originally called Albers-Schonberg disease after the German radiologist who first described it, this form of osteopetrosis is mild.The ones that have this type of osteopetrosis usually are adults between 20 and 40 years old.
Adults with osteopetrosis have frequent bone fractures that don’t heal well. Bone infections (osteomyelitis), pain, degenerative arthritis, and headaches may also occur.
- Intermediate osteopetrosis
There seems to be another type of osteopetrosis that is characteristic to children, appearing in childhood before age 10. It has some of the same symptoms as the malignant infantile form, and might be inherited the same way, but is less severe.
- Other possible forms of osteopetrosis
The following forms are considered by different researchers as being types of osteopetrosis:
- transient infantile osteopetrosis, which is diagnosed early in life, but resolves on its own without treatment
- carbon anhydrase Type II deficiency (CAII) to be yet another form of osteopetrosis. CAII affects the bones, kidneys, and brain, and causes the blood chemistry to change. Children affected by CAII develop calcium deposits in the brain and mental retardation, and about 3/5 of them will develop blindness and/or hearing loss due to bone pressure on the nerves in the skull.
Genetics
The malignant infantile osteopetrosis is transmitted through “autosomal recessive” inheritance. This means that parents do not have any symptoms of the disorder, but they both carry the abnormal gene and will pass the illness to their child. Each child they have has a 1 in 4 chance of having the disorder.
In benign osteopetrosis, a child can inherit the disorder if he/she receives only one defective gene (called “autosomal dominant” inheritance). The children of an adult diagnosed with osteopetrosis have a 50% chance that they, too, have the gene for the disorder and thus might develope the disorder when becoming adults.
Treatment
The treatment includes medication: 1) For both the adult and childhood doctorsadminster Actimmune injections, which delays the progression of malignant infantile osteopetrosis. (mecanism: it causes an increase in bone resorption and in red blood cell production.
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- Bone marrow transplant is the only complete cure available for malignant infantile osteopetrosis. Although it involves many risks, if it is successful it saves the life of a child who would otherwise die from complications of the disorder.
- Other treatments include nutrition, prednisone (helps improve the blood cell count), and physical and occupational therapy.
See also:
http://www.osteopetrosis.org/index.htm