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Greatly increased density of the skeleton Osteopetrosis, also known as marble bone disease and Albers-Schonberg disease, refers to a group of rare genetic diseases that are characterized by reduced bone resorption and diffuse symmetric skeletal sclerosis due to impaired formation or function of osteoclasts. The term osteopetrosis reflects the stonelike quality of the bones; however, the bones are abnormally brittle and fracture easily, like a piece of chalk. It occurs in two major clinical forms: 1) an autosomal recessive malignant infantile form, which is the most severe form of this disorder and death, usually occurs in the first decade of life, and 2) a less severe autosomal dominant variant. The main features of this disease are: • Multiple fractures in spite of increased bone density • Anemia as a result of decreased marrow space • Blindness, deafness, and cranial nerve involvement due to narrowing and impingement of neural foramina Other non-neoplastic diseases of bone: • Achondroplasia is one of the most common causes of dwarfism. It is an autosomal dominant disorder characterized by short limbs with normal-sized head and trunk. • Scurvy is caused by a vitamin C deficiency. It is characterized by bone lesions leading to impaired osteoid matrix formation which is caused by the failure of the proline and lysine hydroxylation required for collagen synthesis. • von Recklinghausen disease of bone (osteitis fibrosa cystica) is caused by primary or secondary hyperparathyroidism. Widespread osteolytic lesions are characteristic. • Osteomalacia is caused by a vitamin D deficiency in adults. Defective calcification of osteoid matrix is characteristic. • Rickets is caused by a vitamin D deficiency in children. • Fibrous dysplasia is characterized by normal bone being replaced by fibrous tissue. There are three classifications depending on extensiveness of skeletal involvement: (1) Monostotic: one bone, (2) Polyostotic: more than one bone, and (3) Polyostotic with associated endocrine disturbances (Albright’s syndrome). Pathologic fractures are often the presenting complaint.