Genes that cause short-sightedness discovered

Behind the Headlines

Tuesday February 12 2013

Myopia is one of the most common eye conditions

'Eye gene discovery may end the need for glasses,' is the somewhat optimistic headline in the Daily Express. The story looks at a wide-ranging and well conducted study that has also been reported on by the Daily Mail and The Independent. 

The study investigated whether certain genes increase the risk of developing refractive errors, which are errors in the way the eye focuses light. Researchers were especially interested in genes that increase the risk of short-sightedness (myopia).

The researchers looked for genetic variants associated with refractive errors among more than 45,000 people. They found 26 genetic variants, two of which had previously been linked to refractive errors, plus 24 new variants. They then calculated that people carrying all the genetic variants were 10 times more likely to become short-sighted.

Sadly, learning more about the genetics of short-sightedness doesn't automatically lead to new treatments – at least not in the short-term. As the Mail rightly pointed out, "any drug to prevent [the] condition is at least 15 years away."

 

Myopia

Short-sightedness is a refractive eye condition caused by a defect in the eye's structure that creates errors in the way the eye focuses light. Instead of focusing on the retina at the back of the eye, light focuses in front of it.

 

Most people are born slightly long-sighted (where close objects appear blurred) because their eyes haven't grown to their full length.

 

Short-sightedness usually happens when the eye continues to grow too long from front to back. As a result, light rays don't reach the back of the eye. This means that objects in the distance seem blurred.

Where did the story come from?

The study was carried out by an international team of researchers called the Consortium for Refractive Error and Myopia (CREAM). This study included data from several other studies, which were mainly funded by governments.

It was published in the peer-reviewed journal Nature Genetics.

The discovery of genetic variants can feed into research into how errors develop in the way eyes focus light. It is hoped that treatments can be developed once this is better understood, but the timescale for any developments is unknown.

The Express' slightly overblown headline was followed by a brief but accurate report. While the Mail's headline, 'Found, genes that could save millions from short-sight and lead to a drug to combat condition,' was also a bit too hopeful, its story did cover the results of the study accurately and struck an appropriate tone of cautious optimism.

The Independent's story was also largely good. However, its online and print versions differed, with the internet version being sensible and accurate, using the headline 'Scientific breakthrough in study of the genetics of myopia.' However, The Independent's newspaper headline, 'Outdoor play "can prevent childhood short-sightedness",' appears to be based on an aside made by one of the researchers and is not founded on any of the evidence presented in the published study.

 

What kind of research was this?

This was a meta-analysis combining the results of 32 studies from Europe, the United States, Australia and Asia. Twenty-seven of the studies included people of European ancestry and five studies included people of Asian ancestry.

The researchers performed a genome-wide association study to see if they could identify genetic variants that were associated with refractive errors (errors in focusing light that often result in reduced vision). 

Genome-wide association studies are an excellent method of identifying genetic variants that may be associated with diseases. They involve taking a sample of DNA and then studying the millions of different genetic variations in the human genome contained in the sample.

However, it still remains to be determined how the genetic variants found affect the eye. The development of treatments that could prevent or correct eye defects is a long way off, despite headlines in the papers that suggest that the results of this study could end the need for glasses.

 

What did the research involve?

The researchers initially performed a genome-wide association study to look for genetic variants that were associated with worse "spherical equivalent". Spherical equivalent is a measure of the eye's focusing power and corresponds to the strength of lens needed to correct a deficiency in focusing (the worse a person's vision, the stronger the lens needed to correct it).

The researchers first used data from 37,382 individuals from the 27 studies of people of European ancestry. They then looked at whether the genetic variants identified in the European cohorts were linked to refractive error in 8,376 individuals from five studies of people of Asian ancestry.

A genome-wide meta-analysis was performed using data from all the individuals (45,758 people in total). The influence of the genetic variants on the risk of developing myopia (short-sightedness) was then calculated.

Finally, the researchers speculated on how the genetic variants could influence the development of refractive error and myopia.

 

What were the basic results?

The researchers identified 309 single nucleotide polymorphisms (SNPs, which are variations in a single DNA base) that were associated with refractive error. These SNPs were located in 18 different regions of the genome.

They took the 18 SNPs with the strongest association with refractive error and tested whether they were associated with refractive error in people of Asian ancestry. Ten of the SNPs were found to be statistically associated with refractive error in this population.

The researchers also found eight further SNPs that were significantly associated with refractive error when they combined the data for all 45,758 individuals.

In total they identified 26 SNPs associated with refractive error. Two of the SNPs had already been described, while the other 24 SNPs were new.

The researchers then looked at how having these SNPs corresponded with the risk of developing refractive errors using data from studies performed in Rotterdam.

People identified as being at high genetic risk (who had the identified SNPs) were found to have a tenfold increased odds of becoming myopic (odds ratio of 10.97, 95% confidence interval (CI) 3.37 to 31.25).

The researchers found that many of the SNPs identified were located in or near genes that code for proteins produced in the retina of the eye. They state that many of the genes identified could play a role in the development of refractive problems.

 

How did the researchers interpret the results?

The researchers conclude that they have identified 24 new genetic positions associated with errors in the way the eye focuses light, resulting in impaired vision. People carrying the highest number of genetic risk factors have a tenfold increased risk of myopia.

The researchers go on to say that further research into how these genetic variants affect eye growth could lead to improved vision for people with myopia.

 

Conclusion

This study has identified 26 genetic variants found to be associated with problems in the way the eye focuses light (refractive errors). Two of the variants were linked to refractive errors previously, and 24 of the variants were new.

Using data from people enrolled in a cohort study in Rotterdam, the researchers calculated that people with the most adverse genetic variants (those with the highest risk score) had a tenfold increase in the odds of becoming short-sighted. The highest risk score occurred in less than 5% of subjects.

Although this is exciting research, contrary to some of the headlines, treatments or prevention strategies are likely to be a long way off. The discovery of genetic variants can feed into research into how errors in focusing light develop. Once this is better understood, it is hoped that treatments can then be developed, but this is far from guaranteed and the timescale for any developments is unknown.

Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter.

Analysis by Bazian

Edited by NHS Choices

Links to the headlines

Found, genes that could save millions from short-sight and lead to a drug to combat condition. Daily Mail, February 10 2013

Scientific breakthrough in study of the genetics of myopia. The Independent, February 10 2013

Eye gene discovery may end the need for glasses. Daily Express, February 11 2013

Links to the science

Verhoeven VJM, Hysi PG, Wojciechowski R, et al. Genome-wide meta-analyses of multiancestry cohorts identify multiple new susceptibility loci for refractive error and myopia. Nature Genetics. Published online February 10 2013

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