Osteopetrosis

Thickening of the bones which become abnormally dense due an inherited defect in bone resorption — the process in which old bone is broken down and removed so that new bone can be added to the skeleton. Osteoclasts are the cells responsible for bone resorption. In osteopetrosis the osteoclasts do not perform normally. This flaw in bone resorption results in bones that are abnormally dense, yet are fragile and easily broken. Men and women are equally affected by the disease. The increased bone mass in individuals with osteopetrosis can limit the amount of available space within the bone marrow. Since the bone marrow is responsible for the production of blood cells, impaired bone marrow function can produce several clinical problems. For example, interference with red blood cell production can lead to anemia. Impairment of white blood cell production can limit the body's ability to fight infection. When platelet production is suppressed, individuals are prone to bleeding since platelets are essential for clotting blood. Anemia, infection, and bleeding are just some of the symptoms that individuals with osteopetrosis can experience —blindness, deafness and even stroke can occur when the skeleton is so dense that blood vessels and nerves cannot pass through the bones. Three major types of osteopetrosis have been identified: {{}}Malignant infantile form — this disease is usually discovered in the first months of life. Hence the term "infantile." The children have the full disease and, in addition, they may have significant delays in psychomotor and tooth development. This form of the disease can be severe, often resulting in death during the first decade of life. This disease is inherited as an autosomal recessive trait — so brothers and sisters of a patient are each at 25% risk to have the same disease. The gene has been found on chromosome 11 in region 11q13.4-q13.5 and is a mutation in what is called the TCIRG1 subunit of the vacuolar proton pump. Adult form — this form is milder and more benign than the infantile form. It generally does not alter life expectancy. Many of the individuals with it have few or no symptoms. It is inherited from generation to generation as an autosomal dominant trait. Males and females with it have a 50% chance of transmitting the gene to each of their children. The gene is on chromosome 1 in region 1p21. Intermediate form— this type of the disease is found in children younger than 10. It tends to be less severe than the malignant infantile form, but more severe than the adult form. Individuals with this type of osteopetrosis generally do not have a reduced life expectancy.

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Excessive formation of dense trabecular bone and calcified cartilage, especially in long bones, leading to obliteration of marrow spaces and to anemia with myeloid metaplasia and hepatosplenomegaly beginning in infancy, to bone fragility, and to progressive deafness and blindness; autosomal dominant inheritance. There are also autosomal recessive forms, which may be mild [MIM*259710], severe [MIM*259700], or lethal [MIM*259720], and sometimes involve a renal tubular defect [MIM*259730]. A milder, autosomal dominant form has onset in childhood and no neurologic sequelae. SYN: Albers-Schönberg disease, marble bone disease, marble bones. [osteo- + G. petra, stone, + -osis, condition]

- o. acro- osteolytica SYN: pyknodysostosis.

- o. with renal tubular acidosis SYN: carbonic anhydrase II deficiency syndrome.

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os·teo·pe·tro·sis -pə-'trō-səs n, pl -tro·ses -.sēz a condition characterized by abnormal thickening and hardening of bone: as

a) a rare hereditary disease characterized by extreme density and hardness and abnormal fragility of the bones with partial or complete obliteration of the marrow cavities called also Albers-Schönberg disease, marble bone disease, marble bones

b) avian leukosis of chickens marked by great enlargement and excessive calcification of the long bones esp. of the legs and by more or less complete obliteration of the marrow cavities called also marble bone, marble bone disease

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n.

a congenital abnormality in which bones become abnormally dense and brittle and tend to fracture. Affected bones appear unusually opaque to X-rays. In severe forms the bone marrow is obliterated, causing anaemia and infections. Treatment is by bone marrow transplantation. See also osteosclerosis.

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os·teo·pe·tro·sis (os″te-o-pe-troґsis) [osteo- + Gr. petra stone + -osis] a rare genetic disease characterized by abnormally dense bone, due to defective resorption of immature bone. It occurs in two forms: a severe autosomal recessive form occurring in utero, infancy, or childhood, and a benign autosomal dominant form occurring in adolescence or adulthood. In the recessive form, the proliferation of bone obliterates the marrow cavity, causing anemia and hepatosplenomegaly, and narrowing the foramina of the skull, causing compression of cranial nerves, which may result in deafness and blindness. Fractures are common in both forms. Called also Albers-Schцnberg or marble bones disease, ivory bones, and marble bones.