These bone cells are responsible for breaking down bone. When they fail, bone formation by osteoblasts is unopposed, and thick, dense bones are formed.
This enzyme is present inside osteoclasts and if a patient has a mutation in the CA2 gene, they will be deficient of the enzyme and bone resorption will fail to occur. A mutation in the CLCN7 gene will cause a hydrogen-chloride channel dysfunction with a similar outcome.
Osteoclasts normally utilize carbonic anhydrase to make a local acidic environment that is necessary for the breakdown of bone matrix within a resorption pit. Enzyme deficiency halts this process.
Although the unopposed osteoblasts produce thick and heavy bone, it is fragile and prone to breakage just like a piece of marble. Therefore, these patients have an increased incidence of fractures.
As bones thicken in the skull, they compress any surrounding structures, including nerves. This may cause a multitude of cranial nerve palsies and manifest with symptoms of paralysis, paresthesias, and hearing and vision impairment.
As bone mineralization continues uninhibited, it replaces bone marrow. Whenever bone marrow is displaced by another tissue, it is called a myelophthisic process. Lack of functioning bone marrow results in anemia, thrombocytopenia, and leukopenia.
Radiographs often depict a distal flaring of long bones on either end, producing a plain film image that resembles an Erlenmeyer flask.
As a way to distinguish osteopetrosis from Paget’s, alkaline phosphatase will be normal in this disease. Parathyroid hormone is not involved in pathology and remains unaffected.
On lab evaluation, osteopetrosis patients have normal calcium and phosphate levels. Only in late and severe presentations will a decreased calcium value be identified.
Overly thick and dense bones produce a characteristic x-ray image in which it appears that a bone has another bone inside of it.
Since a patient lacks functional osteoclasts, the only available treatment is to perform bone marrow transplant and allow for monocyte evolution into new osteoclasts.
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