Bones are constantly being remodeled, and the process is carefully controlled to ensure that bones stay strong and healthy. Mutations in any of the genes associated with osteopetrosis lead to abnormal or missing osteoclasts. Without functional osteoclasts, old bone is not broken down as new bone is formed. As a result, bones throughout the skeleton become unusually dense. The bones are also structurally abnormal, making them prone to fracture. These problems with bone remodeling underlie all of the major features of osteopetrosis. Diagnosis
The differential diagnosis of osteopetrosis includes other disorders that produce osteosclerosis. They constitute a wide array of disorders with clinically and radiologically diverse manifestations. Among the differential diagnosis are hereditary ostoesclerosing dysplasias such as; neuropathic infantile osteopetrosis, infantile osteopetrosis with renal tubular acidosis, infantile osteopetrosis with immunodeficiency, infantile osteopetrosis with leukocyte adhesion deficiency syndrome (LAD-III), pyknodysostosis (osteopetrosis acro-osteolytica), osteopoikilosis (Buschke–Ollendorff syndrome), osteopathia striata with cranial sclerosis, mixed sclerosing skeletal dysplasias, progressive diaphyseal dysplasia (Camurati–Engelmann disease), SOST-related sclerosing skeletal dysplasias. Besides, the differential diagnosis includes acquired conditions that induce osteosclerosis such as osteosclerotic metastasis notably carcinomas of the prostate gland and breast, Pagets disease of bone, myelofibrosis (primary disorder or secondary to intoxication or malignancy), Erdheim-Chester disease, osteosclerosing types of osteomyelitis, sickle cell disease, hypervitaminosis D, and hypoparathyroidism. Treatment
It was the first genetic disease treated with hematopoietic stem cell transplantation (osteoclasts are derived from hematopoietic precursors). There is no cure, although curative therapy with bone marrow transplantion is being investigated in clinical trials.
Most importantly, osteoclast dysfunction mediates the pathogenesis of this disease.Osteopetrosis is caused by underlying mutations that interfere with the acidification of the osteoclast resorption pit, for example due to a deficiency of the carbonic anhydrase enzyme encoded by the CA2 gene. Carbonic anhydrase is required by osteoclasts for proton production. Without this enzyme hydrogen ion pumping is inhibited and bone resorption by osteoclasts is defective, as an acidic environment is needed to dissociate calcium hydroxyapatite from the bone matrix. As bone resorption fails while bone formation continues, excessive bone is formed.Mutations in at least nine genes cause the various types of osteopetrosis. Mutations in the CLCN7 gene are responsible for about 75 percent of cases of autosomal dominant osteopetrosis, 10 to 15 percent of cases of autosomal recessive osteopetrosis, and all known cases of intermediate autosomal osteopetrosis. TCIRG1 gene mutations cause about 50 percent of cases of autosomal recessive osteopetrosis. Mutations in other genes are less common causes of autosomal dominant and autosomal recessive forms of the disorder. The X-linked type of osteopetrosis, OL-EDA-ID, results from mutations in the IKBKG gene. In about 30 percent of all cases of osteopetrosis, the cause of the condition is unknown.The genes associated with osteopetrosis are involved in the formation, development, and function of specialized cells called osteoclasts. These cells break down bone tissue during bone remodeling, a normal process in which old bone is removed and new bone is created to replace it.