Short-sightedness, or myopia as it is technically known, affects around a quarter of the UK population and its incidence is on the increase around the world. In Singapore the percentage of the population with myopia rose from 25 per cent to 80 per cent in the last 30 years, with estimates of 90 per cent in some Asian populations. The increasing importance of this condition has led to research into its causes and now a team from St Thomas' Hospital in London have found a genetic link.
The St Thomas' research team compared the DNA of 221 pairs of twins, some identical, some non-identical. As identical twins have the same genetic make-up it is possible to work out what affect environmental factors, such as reading and watching television, might have on their eyesight. The team found genetic sequences on chromosome 11 that were common to myopic children. Though not in a gene, these sequences are thought to impact upon a nearby gene called PAX6.
Dr Chris Hammond, the consultant ophthalmologist who led the research, ruled out a mutation in the PAX6 gene. He said that PAX6 is fundamental to eye development and that 'most mutations in this gene cause major eye abnormalities, as you would expect for such an important gene'. Instead, he thinks these genetic sequences affect the turning on and off of PAX6 and hence the turning on and off of eye development. He 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'.
The research, published in the August edition of the American Journal of Human Genetics, builds on earlier work that indicated that genetic factors account for 89 per cent of the causes of myopia. Hammond said, 'we hope to start working out the mechanics of how people become short-sighted'.
Despite the genetic link, Hammond warned parents about the environmental factors that may compound any genetic disposition. 'Try moving the television further away from the sofa, don't let your children play computer games or surf the net for hours on end, and ensure that they get out of the house to enjoy the summer sun', he said.
Sources and References
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Key myopia gene found in twin study
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Gene linked to short-sightedness
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Gene that enhances myopia risk identified
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Myopia researchers are starting to see double
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