Nearsightedness runs in families, but the genetic factors that lead people to need vision-correcting glasses or contact lenses have been poorly understood. Now, research on monocled mice and myopic families finds strong evidence linking severe nearsightedness to mutations in the SCO2 gene, which helps metabolize the mineral copper and regulate oxygen levels in eye tissue. The results, published today in the American Journal of Human Genetics, suggest that copper deficiencies could put people at risk for poor vision.
Nearsightedness, or myopia, happens when an eye is unable to correctly focus images because its shape is too long or the cornea, the front part of the eye, is too curved.
Myopia affects a third of American adults and is the most common human eye problem in the world. Previous research has suggested that it results from a combination of genetics and environmental factors, like reading a lot at a young age.
Researchers led by Dr. Terri Young of Duke University looked for genetic clues linked to nearsightedness by focusing on people with high-grade myopia, a more severe and highly heritable form that puts people at greater risk for debilitating eye problems.
High-grade myopia affects as many as two percent of Americans, and while it is more common among people of Asian ancestry, the researchers started by focusing on four close relatives from a European-American family with the condition.
Deep sequencing of DNA extracted from the relatives' blood and saliva samples revealed that family members with high-grade myopia had particular mutations in the SCO2 gene, while those without any myopia did not have those variations.
Researchers further examined the link by sequencing the SCO2 genes of 140 additional people with high-grade myopia, confirming four mutations in that region of DNA.
To examine how this gene might affect vision, they examined human eye tissue and found that proteins were more highly expressed by the SCO2 gene in parts of the eye related to nearsightedness, like the retina, sclera, choroid, and retinal pigment epithelium.
Lastly, they conducted an experiment on mice in which a strong lens attached to one eye made them nearsighted- a monocle that actually worsened their vision. Analysis showed that SCO2 protein expression decreased in the nearsighted eye while remaining the same in the other, suggesting that the protein is involved in the onset of myopia.
The researchers suggest that since copper metabolism is necessary for eye health, and the SCO2 gene helps metabolize copper, copper deficiency might increase a person's risk for nearsightedness-especially if they have the SCO2 gene mutations identified in this study.
"While this wasn't directly tested in this study," said Young in a statement, "it's possible that our diets -- which are deficient in a number of minerals and vitamins -- play a role, and it may be something as easy as taking a supplement with copper that helps thwart the development of myopia."
It's important to note that there's no one factor that leads to nearsightedness, and Young expects that future research can detail whether and how much copper supplements can really help, as well as what other mechanisms are involved in producing myopia.