rare hereditary congenital disorder in which the bones (bone) become extremely dense, hard, and brittle. The disease progresses as long as bone growth continues; the marrow (bone marrow) cavities become filled with compact bone, and severe anemia results. In marble bone disease, bone-resorbing cells called osteoclasts (osteoclast) are either reduced in number or are ineffective. Fractures (fracture) are frequent; deafness and loss of vision may occur because cranial nerves (cranial nerve) become compressed by the narrowing of their passageways as bone is deposited in the skull. Severe cases may be fatal; individuals with mild cases of the disorder may have a normal life expectancy. Treatment may include gamma interferon, a protein that delays progression of the disease; bone marrow transplantation; or calcitriol, a vitamin D compound that stimulates osteoclasts to dissolve and absorb bone.