Osteopetrosis

Osteopetrosis, literally bone becoming stone and also called marble bone disease or Albers-Schönberg disease, is an extremely rare inherited disorder in which the bones become abnormally hard and dense because the osteoclasts, the cells responsible for breaking down old bone tissue, fail to develop or function properly, unlike osteoporosis in which the bones become weak. The condition follows autosomal dominant, autosomal recessive or, less commonly, X-linked recessive inheritance patterns depending on which gene is affected. Despite the excess bone formation, the resulting bone is paradoxically more brittle than normal bone and fractures more easily. Mild forms may cause no noticeable symptoms, but severe forms can produce stunted growth, anemia, recurrent infections and neurological complications such as blindness, facial paralysis and deafness caused by the extra bone pressing on nerves as they pass through narrowed skull openings.