Mutations in a gene that helps regulate copper and oxygen levels in eye tissue are associated with a severe form of nearsightedness, according to a study at Duke Medicine.

Nearsightedness - also known as myopia - is the most common human eye disease in the world. It occurs if the eye is too long or the cornea has too much curvature, which keeps light entering the eye from focusing correctly.

High-grade myopia, a more severe form of nearsightedness, affects up to two percent of Americans and is especially common in Asian populations. Individuals with high-grade myopia are at an increased risk for other serious eye problems, including retinal detachment, cataracts and glaucoma.

Studies suggest that myopia is caused by a combination of environmental factors, such as large amounts of reading, and genetics. Nearsightedness runs in families, but little is understood about genetic factors that cause it.

In recent years, researchers have reported several genes or locations of genes associated with myopia, and have continued to search for additional clues.

"This is the first time a gene mutation for autosomal dominant nonsyndromic high-grade myopia in Caucasians has been discovered," said senior author Terri Young, M.D., MBA, professor of ophthalmology, pediatrics and medicine at the Duke Eye Center, Duke Center for Human Genetics and the Duke-National University of Singapore Graduate Medical School (Duke-NUS).

In this study, Young and her colleagues sought to identify these genetic factors by studying families with high-grade myopia. They performed next-generation deep sequencing on four relatives from an 11-member American family of European descent.

Analyzing DNA extracted from blood and saliva, the researchers identified mutations in the SCO2 gene in common among family members with high-grade myopia, but absent in those family members with no myopia. They confirmed four mutations in the SCO2 gene in an additional 140 people with high-grade myopia.