Scientists 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 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.
This is the first known evidence of gene-environment interaction in myopia," says the study's lead investigator. The research was published in PLOS Genetics.
Although it's not yet known how genetic variation at the APLP2 gene causes myopia, reserachers 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.
"Once the eye has elongated, you cannot shrink it, so we would need to identify kids with genetic risk factors as they enter school," author says. That's not yet possible because there are probably hundreds of genes that can cause myopia, and so far, only 25 candidates have been identified. The high-risk variant of APLP2 is relatively uncommon, occurring in about 1 percent of the population.