Osteopetrosis: A genetic disease that is characterized by abnormally dense thick bone. A severe autosomal recessive form of osteopetrosis can occur in infants and children, and a milder autosomal dominant form can occur in teens and adults. In the recessive form, the thickened bone obliterates the marrow cavity, causing anemia, and ?narrows the openings of the skull, causing compression of nerves to the ears and eyes, ultimately resulting in deafness and blindness. Fractures are common in both forms. Also known as marble bone disease.