Gene that causes myopia discovered

Researchers have discovered a gene that causes myopia, but only in people who spend a lot of time in childhood reading or doing other 'nearwork.'
Using a database of approximately 14,000 people, the researchers at Columbia University Medical Center found that those with a certain variant of the gene - called APLP2 - were five times more likely to develop myopia in their teens if they had read an hour or more each day in their childhood.
Those who carried the APLP2 risk variant but spent less time reading had no additional risk of developing myopia.
"We have known for decades that myopia is caused by genes and their interactions with environmental factors like reading and nearwork, but we have not had hard proof. This is the first known evidence of gene-environment interaction in myopia," said the study's lead investigator, Andrei Tkatchenko of CUMC.

Although it's not yet known how genetic variation at the APLP2 gene causes myopia, Tkatchenko and his colleagues think the risk variant may increase the amount of APLP2 protein produced in the eye, which in turn may cause the eye to undergo excessive elongation.
They found that mice exposed to a visual environment that mimics reading were less likely to develop myopia when little APLP2 protein was present in the eye.

"By reducing the level of APLP2 in the eye, you can reduce susceptibility to environmentally induced myopia. This gives us an opportunity to develop a therapy to prevent myopia in everyone, regardless of the APLP2 variant they carry," Tkatchenko said.

Developing such a therapy, however, could take years, as researchers don't yet know how APLP2 levels could be reduced in people. And the therapy would be most effective in young children, before the eye has started to elongate and become myopic.
"Once the eye has elongated, you cannot shrink it, so we would need to identify kids with genetic risk factors as they enter school," said Tkatchenko.
That is not yet possible because there are probably hundreds of genes that can cause myopia, and so far, only 25 candidates have been identified, researchers said.
The high-risk variant of APLP2 is relatively uncommon, occurring in about 1 per cent of the population.

Though a drug or gene therapy to prevent myopia may be years away, Tkatchenko said spending time outdoors is the best way to reduce kids' risk of developing myopia.
"We pretty much know all the environmental risk factors: time spent reading increases the risk, while time spent outdoors reduces it," said Tkatchenko.
The research was published in PLOS Genetics.