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Osteopetrosis is an extremely rare inherited disease which causes the bones of the suffer to increase in density. It is sometimes called “Marble Bone Disease,” in a reference to the extreme hardening of the bones involved, and it is also known as Albers-Schonberg Disease. Currently, osteopetrosis is not curable, although there are ways to make patients more comfortable, and researchers hope that they can identify the rogue gene which causes the condition.
Two main cells regulate the growth and density of bone in the body. Osteoblasts generate new bone, while osteoclasts destroy bone and reabsorb its minerals. Most people have a proper balance of these cells which promotes the growth of new healthy bone and the dissolution of older bone. In patients with osteopetrosis, however, there are less osteoclasts, meaning that the body keeps growing new bone, but that bone is not reabsorbed.
If you're familiar with your Greek roots, you know that osteo means “bone” and petras means “rock,” suggesting that the patient's bones turn to stone. This is not quite accurate, but it's pretty close. As the patient continues to grow new bone, the overall bone density increases, and it is not uncommon for patients to experience pain around their bones as a result of nerves which are pressured by the extremely dense bone.
Osteopetrosis is often easy to identify on an x-ray, because the patient's dense bones will clearly show. Ironically, despite the fact that the bones are very dense, they are also very brittle. Many osteopetrosis patients suffer frequent and painful fractures, and when the condition appears in adults, this is often the first sign. When osteopetrosis arises in older people, it is known as benign osteopetrosis, although this name is a bit of a misnomer because the condition can still be very painful and potentially deadly.
When osteopetrosis is diagnosed in infants or very young children, it is known as malignant osteopetrosis, and the prognosis is often poor, with some patients not living long beyond the age of 10. Diagnoses which fall between the ends of this spectrum are imaginatively called “intermediate osteopetrosis.” In all cases, steps are taken to make patients more comfortable, and some doctors use bone marrow transplants as a treatment technique, in the hopes that the bone marrow will generate more osteoclasts to help break down the excess of bone.