In the field of rickets and osteomalacia, progress has been made mainly in the mapping of vitamin D-dependency rickets or ldquo;pseudo-deficiency ricketsrdquo; type I to chromosome 12q14, and the further identification of a variety of abnormalities in the calcitriol receptor complex responsible for hereditary resistance to 1,25-dihydroxyvitamin D. The study of the molecular basis of this latter inherited disorder has important implications for a better understanding of the physiologic role of 1,25-dihydroxyvitamin D. Concerning osteopetrosis, the finding of a reverse transcriptase activity in a patient with the benign form of this disorder opens new perspectives such as the possibility that retroviral infection may be the origin of at least some type(s) of osteopetrosis. Moreover, impairment of macrophage colony-stimulating factor production appears to be a key event in the pathogenesis of the osteopetrotic op/op mutation in rodents.
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