Genes and blindness
Some forms of blindness are genetic. Scientists have now identified and localized one of the responsible genes. They hope to pave the way for new forms of therapy. If we follow how the eyes normally develop, then we can also identify the sections in which there are misdevelopments that can cause blindness. Two related articles in the November issue of Cell (November 14, 1997) describe a gene that is important for the formation of photoreceptor cells.
For the first time, a gene has been identified that is defective in cone-rod dystrophy, an inherited form of retinal degeneration.
Constance LCepko and her colleagues at Harvard Medical School found that the gene, called CRX, was active only in developing and maturing retinal photoreceptor cells. They found related genes in the rat and mouse retinas, enabling them to study the timing of gene activity and the effects of dysfunction.
The gene regulates the production of proteins such as opsin (a component of the light-sensitive part of the photoreceptor) and other structures found only in photoreceptors. The CRX is active at the time when developing retinal cells differentiate into either photoreceptors or other signal-harvesting cells. CRX hyperactivity creates too many photoreceptor cells and too few junction cells. On the other hand, if the activity was throttled, the outer segments of the photoreceptors were sometimes malformed.
In the further study that Cepko conducted with Carol L. Freund of the Hospital for Sick Children in Toronto, the human CRX gene was isolated and mapped to a locus associated with a specific type of cone rod dystrophy, CORD-2. The team found that certain mutations in the CRX gene lead to this type of blindness.
The scientists hope that these results will lead to new therapeutic approaches for CORD-2 and other forms of blindness.
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