The study of ocular disorders at the molecular genetics level has opened an opportunity for gene therapeutics m ophthalmology. It has been observed that a number of mutations in the human rhodopsin gene are the cause of autosomal retinitis pigmentosa (83). Besides rhodopsin gene mutations, the gene encoding cGMP phosphodiesterase has been identified in autosomal recessive pigmentosa (84). Some eye disorders like color blindness, choroideremia, and Norrie's disease have genetic linkage with the X chromosome (85—87). Aniridia, color vision and cone dystrophies, Leber's hereditary optic neuropathy, Marfan's syndrome, retinoblastoma, stickler syndrome, uveal melanoma, and von Hippel-Lindau disease are a number of genetic eye disorders m which the defective genez have been identified (88) The localization and identification of disease-causing genes and their products, helps to utilize the potential of gene therapy in a particular ailment. Considering the delivery of a particular gene, the eye has certain advantages as a target for virus-mediated gene therapy. The transfer process can easily be monitored due to easy accessibility, well defined anatomy, and the translucent nature of the eye (89). Theoretically, transfer of retroviral vectors for gene transfer in ocular tissues is limited due to the presence of quiescent or slowly dividing cells, however retrovirus-mediated gene transfer has shown encouraging results in chorioretinal degeneration which is caused by deficiency of the mitochondrial matrix enzyme ornithine-delta-ami-notransferase (90). Replication deficient adenoviruses have shown encouraging results for gene transfer m ocular tissues (91—93). This and similar studies have opened new prospects for the treatment of inherited retinal disorders.
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