Osteopetrosis, also known as “marble bone disease,” causes bone density to increase due to fewer osteoclasts breaking down bone. It is not curable, but treatments aim to make patients more comfortable. In infants, it is malignant and can be life-threatening. Bone marrow transplants may help generate more osteoclasts.
Osteopetrosis is an extremely rare hereditary disease that causes the bone density of sufferers to increase. It is sometimes called “marble bone disease,” referring to the extreme hardening of the bones involved, and is also known as Albers-Schonberg disease. Currently, osteopetrosis is not curable, although there are ways to make patients more comfortable and researchers hope they can identify the rogue gene that causes the condition.
Two master cells regulate the growth and density of bones in the body. Osteoblasts generate new bone, while osteoclasts break down bone and resorb 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 fewer osteoclasts, which means that the body continues to grow new bone, but that bone isn’t being resorbed.
If you’re familiar with your Greek roots, you know that osteo means “bone” and pettras means “rock,” suggesting that the patient’s bones turn to stone. This isn’t entirely accurate, but it’s close enough. As the patient continues to grow new bone, the overall bone density increases and it is not uncommon for patients to experience pain around the bones due to nerves being put under pressure from the extremely dense bone.
Osteopetrosis is often easy to identify on an x-ray, because the patient’s dense bones will show clearly. Ironically, despite the fact that bones are very dense, they are also very fragile. Many patients with osteopetrosis experience frequent and painful fractures, and when the condition appears in adults, this is often the first sign. When osteopetrosis occurs 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 life threatening.
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 10 years. Diagnoses that fall between the ends of this spectrum are fancifully called “osteopetrosis intermedia”. In all cases, steps are taken to make patients more comfortable, and some doctors use bone marrow transplants as a treatment technique, in the hope that the bone marrow will generate more osteoclasts to help break down the excess bone.
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