Researchers say their findings indicate gene therapy is the best approach to treating achromatopsia - a rare form of color blindness.
Achromatopsia is an inherited disorder that affects around 1 in 33,000 people in the US.
The condition is triggered by abnormalities in the retina - a layer of tissue at the back of the eye containing cells that are sensitive to light. People with achromatopsia will experience partial or total loss of color vision, as well as sensitivity to light.
At present, there is no cure for achromatopsia. Current treatments to help manage the condition include the use of red-colored lenses to reduce sensitivity to light and boost visual functioning.
However, ongoing research using animal models has identified gene therapy as a promising avenue for an achromatopsia cure, and this latest study - conducted by researchers from Temple University in Philadelphia, PA, and the University of Pennsylvania - brings the strategy one step closer.
Human achromatopsia mutation found in canine CNGA3 gene
Senior author Karina Guziewicz, of the School of Veterinary Medicine at the University of Pennsylvania, and colleagues began their study by analyzing a German shepherd dog whose owners were concerned about its vision.
- Total color blindness as a result of achromatopsia is more common than partial color blindness
- In order for a child to inherit achromatopsia, both the mother and father must be carriers of an achromatopsia gene mutation
- There are around 100 different mutations in the CNGA3 gene that have been linked to achromatopsia in humans.
"This dog displayed a classical loss of cone vision; it could not see well in daylight but had no problem in dim light conditions," explains study coauthor Gustavo Aguirre, professor of medical genetics and ophthalmology at the School of Veterinary Medicine.
The researchers set out to identify the genetic cause of the dog's vision loss, though they found none of the known gene mutations that lead to achromatopsia in dogs.
By analyzing five genetic mutations known to play a part in how light signals are sent from the eye to the brain - a process called phototransduction - the team identified a mutation in a gene called CNGA3 that was responsible for the German shepherd's vision loss.
On analyzing Labrador retrievers that had similar symptoms of vision loss to the German shepherd, the researchers identified a different mutation on the same area of the CNGA3 gene where the German shepherd's mutation was found.
The team notes that these mutations have never before been identified in dogs, but the gene mutation found in the German shepherd have been found in humans, highlighting dogs as a valuable model in which to study human achromatopsia.
Gene therapy the 'best approach' to treating achromatopsia
Next, the team adopted a supercomputer technique that allowed them to identify small changes in protein sequences that may have important implications for visual signaling.
From this, they found that the two mutations found in the CNGA3 gene of dogs impaired the function of the cyclic nucleotide channel, which plays a major role in converting visual signals.
These findings, the researchers say, offer new insights into the molecular mechanisms underlying achromatopsia and emphasize the potential for gene therapy to cure the condition in both dogs and humans.
"Our work in the dogs, in vitro and in silico shows us the consequences of these mutations in disrupting the function of these crucial channels.
Everything we found suggests that gene therapy will be the best approach to treating this disease, and we are looking forward to taking that next step."
Medical News Today recently reported on the first successful transplantation of stem cell-derived eye cells behind the retina of a patient with wet age-related macular degeneration (AMD) - a procedure that brings us closer to a cure for the disease.