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Gene focuses search for cause of myopia


How far can you see? (Image: iStockphoto)

A gene basic to how the eye develops may also hold the key to being short-sighted, U.K. researchers say.

They say their findings reinforce the still-debated idea that some children are born susceptible to being short-sighted, and that too much reading or close work can encourage it.

The gene, called PAX6, may be involved in the growth of the eye, said the researchers at St Thomas' Hospital in London, who published their findings in the August issue of the American Journal of Human Genetics.

Short-sightedness or myopia is caused when the eyeball grows too long.

"It may well be that too much close work may be bad for your eyes, particularly if you have a susceptibility," said lead author Dr Chris Hammond.

"We know ... that what makes one person shortsighted and another person longsighted is a genetic difference between them rather than any difference in environment. But we also know environmental effects are powerful and close work is the culprit."

For their study, Hammond and colleagues screened 221 pairs of non-identical twins, looking at their genetic makeup.

They found common genetic sequences on chromosome 11 in the myopic children. When they looked closer, they found the suspect area was very close to PAX6.

"PAX6, the gene that we have found to be linked to myopia, is a fundamental gene to eye development," Hammond said.

"It is very highly conserved across lots of species. And when we see a gene that is very highly conserved, from the fruit fly to zebrafish to humans, we know it has a very important role in development. For instance if we put it onto the leg of a fruit fly, it will grow an eye on its leg. It's that important."

Not a mutation

But Hammond's team says it does not appear that a mutation in PAX6 causes myopia.

"Most mutations in this gene cause major eye abnormalities, as you would expect for such an important gene," Hammond said. "It's so important that you can't play with it."

What is probably happening is that a nearby genetic region is regulating the gene, and variations in that region cause myopia.

Myopia is becoming more common and some researchers believe it is the increasing tendency of children to stay indoors watching television, playing computer games and reading, that is to blame. Obesity research also supports this theory.

It may be that genetic variation, combined with environmental cues, interfere with a natural cut-off in eye growth, Hammond said.

"Most children are born long-sighted and the eyes grow until they reach normal sight and stop growing, but myopic eyes don't stop growing," Hammond said.

As a result, images focus too far in front of the retina to be clear.

His team will look for the regulators of PAX6 now. In the meantime, his advice to parents is to encourage children to play outside.

Tags: health, biology, cloning-and-dna