Scientists researching an inherited vision disorder called achromatopsia, which robs people of color vision and leaves them in a black-and-white world, say they've found a previously unknown genetic mutation involved in the disorder.

All over the world there are entire families with this type of vision defect, researchers say, strongly suggesting a genetic root cause that can be passed down from parent to child.

There have been a number of genetic mutations already associated with achromatopsia and its degraded visual acuity and limited or complete lack of color vision, researchers say.

"But we still had families that didn't have any of those gene mutations," says Jonathan Lin, an associate professor of pathology at the University of California, San Diego. "We knew this meant there must be other genes and proteins involved."

Lin is a senior author of a paper describing their search for additional genetic underpinnings of the condition, published in the journal Nature Genetics.

The researchers discovered a mutation in a single gene known as ATF6 caused proteins involved in the functioning of cone photoreceptors in the eye to be damaged.

The human eye contains millions of cone photoreceptors, which are responsible for daytime vision and color recognition.

Achromatopsia is unlike a more prevalent version of colorblindness that leaves some people unable to distinguish between the colors green and red, Lin explained.

Achromatopsia sufferers' vision only provides images on a gray scale, completely devoid of color, he says. They also are often very sensitive to light.

In serious cases, people with achromatopsia "can't drive, read, watch TV or have a job," Lin says. "With that level of vision, they are functionally blind."

The disorder affects around 10,000 people in the U.S., the researchers report.

In their study, the researchers performed genetic testing on 18 individuals with achromatopsia from 10 families who lacked any of the other previously known genetic mutations associated with the disorder.

Using gene-sequencing technology on blood samples from the study participants, researchers found the gene mutation of ATF6 in all 18.

When it is working properly, the ATF6 gene is an important regulator of a process known as the unfolded protein response, or UPR, critical to the proper workings of the cellular proteins involved in various biological functions of the body

"In this particular disease, we think a mutation in the ATF6 gene disrupts the UPR process and causes the production of bad proteins which keep cone photoreceptors from functioning properly," Lin says.

There is reason to believe the ATF6 mutation may also be involved in much more prevalent eye diseases including retinitis pigmentosa and macular degeneration, which also involve loss or poor functioning of cone photoreceptors, the researchers suggest.

While there is currently no cure or treatment for achromatopsia, the study findings are encouraging as a starting point, Lin says.

"It's early days yet," he says. "But pinpointing the genetic cause allows us to focus on finding a way to block this mutation."

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