Osteopetrosis. Coloured X-ray of the forearms of a child with osteopetrosis, seen as a thickening of the arm bones at lower left and right. Osteopetrosis, also known as marble bone disease and Albers-Schonberg disease, is a rare inherited disorder where the bones harden, becoming denser than normal. Bone growth is a balance between osteoblasts (cells that create bone tissue) and osteoclasts (cells that break down bone tissue). Those with osteopetrosis have a deficiency in osteoclasts and produce too much bone. Mild osteopetrosis results in slightly more brittle bones, but severe cases can lead to growth deformities, blindness, deafness and paralysis due to the extra bone interfering with nerve function. There is no known cure for this disease.