Over The Horizon

Making the Blind to See

An Otago University research team has announced a major breakthrough in the search for a cure for retinitis pigmentosa (RP), an inherited eye disease which affects about 1000 New Zealanders and up to four million people worldwide.

The disease causes progressive degeneration of the photoreceptor (light-detecting) cells of the retina, leading to night blindness, tunnel vision and, eventually, to blindness.

Working in collaboration with Professor Andreas Gal of the Institute of Human Genetics in Hamburg, Otago researchers Drs Mike Denton and Marion Maw have discovered defects in two genes found in the retinal epithelium -- a layer of cells found at the back of the eye. The genes provide instructions for two proteins that play a vital role in transporting vitamin A to the eye's light-detecting cells, which require a continuous supply of the vitamin to function properly. (Vision is impossible without vitamin A.)

The researchers discovered the defects in the genes using DNA and protein analysis from a study of 20 Indian families. Denton says these families were collected through many years of dedicated effort by a number of Indian collaborators including two leading eye hospitals, Sankara Nethralaya in Chennai, and Little Flower Hospital in Kerala.

Denton, a molecular geneticist in the University's biochemistry department, says for many years researchers have been searching for a cure for RP, the most common form of inherited blindness in young adults throughout the world. Although much progress has been made in understanding the basic nature of the disease, none of these advances has held out any realistic hope for a cure in the short term.

The new results, however, provide the first evidence that defects in proteins found in the retinal epithelial cells can cause the disease. Before this discovery, the only defects implicated in RP were found in the eye's photoreceptor cells which are part of the neuroretina.

Denton says the discovery is medically significant because, compared to the neuroretina, which has a complex structure, the epithelial layer is relatively simple and much more amenable to therapies such as transplantation and vitamin A supplementation.

"This finding is very exciting because it seems likely that the application of these therapies may lead to a cure for some families in the near future," Denton says. "Transplantation of the retinal epithelial cells is a new technique which has only recently been carried out in humans on an experimental basis. If transplantation can be perfected and the transplanted cells are able to survive a lifetime, that would be a cure.

"I am confident that transplantation will eventually be used to treat certain types of these diseases, although I would not envisage it would be available as a routine treatment for ten years."

As far as vitamin A supplementation is concerned, Denton expects more immediate benefits for a proportion of RP sufferers.

"I have no doubt that some defects in the epithelium tissue will respond to vitamin A and that some cases will effectively be cured by this means. In my view, this is certainly one of the most important results from the study of genetics of the retina since the early 1980s because it is the first finding which offers a real hope for a proportion of RP sufferers."