Researchers have identified a previously unknown gene mutation that causes sufferers to be either totally or predominantly colourblind and see the world in black, white and shades of grey.
Researchers at the University of California, San Diego School of Medicine and Shiley Eye Institute at UC San Diego Health System identified the gene mutation that underlies achromatopsia, an inherited eye disorder.
People with achromatopsia have very poor or no colour vision and see the world in black, white and shades of grey. They also have reduced visual acuity and are sensitive to light.
This type of colourblindness is different from the more common version, which makes some people unable to distinguish between red and green.
"We're very excited to have discovered a mutation in the ATF6 gene which plays a major role in this disorder," said Jonathan Lin, senior study author and an associate professor in the UC San Diego School of Medicine Department of Pathology.
Five other genetic mutations have previously been identified by research groups as pivotal in achromatopsia.
"But we still had families that didn't have any of those gene mutations. We knew this meant there must be other genes and proteins involved," Lin said.
The new study found that a mutation in the ATF6 gene damaged proteins necessary for proper function of the eye's cone photoreceptors.
In the study, the scientists looked at 18 achromatopsia patients from 10 different families who had been identified as lacking the five previously known gene mutations.
The families received testing in the lab of Susanne Kohl, the study's first author from Centre for Ophthalmology at University of Tuebingen in Germany.
Blood drawn from study subjects was analysed using gene sequencing technology. All 18 were found to have the ATF6 gene mutation.
Lin said the ATF6 gene, when working properly, is a key regulator of the unfolded protein response (UPR).
The UPR is a critical player in helping the body's cellular proteins work correctly, which is extremely important since proteins carry out many biological functions.
"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," said Lin.
Lin noted that the UPR is a different molecular mechanism than those affected by the other five gene mutations.
"We're really excited because this (UPR) is a new pathway found to be involved in this disease," he said.
The discovery raises the possibility that the ATF6 gene mutation, and subsequent UPR dysfunction in the cone photoreceptors, may be related to other much more common eye diseases, such as macular degeneration and retinitis pigmentosa, which involve the loss of cone photoreceptors, said Lin.
