Retroviruses and bone diseases.
In 1980, retroviruses were shown to be pathogenic to humans, and experimentation on animals involving retroviruses as causal agents of tumors and degenerative diseases of bone, brain, and lung gained interest. Osteopetrosis, which can be either inherited in rodents or retrovirally induced in cats, is exemplary. Because of replication cycle, retroviruses can be propagated not only as infectious agents but also as cellular genes. If a retroviral infection occurs in germ line cells, the viral genes, which must integrate in the host's DNA, can be passed on to the progeny and inherited as Mendelian characteristics. Therefore, a retroviral etiology could account for diseases that present either as sporadic (infectious) or familial (inherited), although they may be similar in their clinical manifestations. This approach led to the finding of 2 new human retroviruses: 1 in a patient who had sporadic benign osteopetrosis, and the other in a patient who had sporadic paraarticular osteoma. In both patients, the retrovirus was isolated from mononuclear blood cells, not from bone cells, because of the links between bone and the immune system. A systematic search for retroviruses in patients who have sporadic bone disease, which also may appear as inherited disease, has yet to be performed. Patients with sporadic disease could be managed by antiretroviral agents such as Zidovudin.