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Researchers have – for the first time ever – found a form of congenital night blindness in dogs. There are a number of different conditions that can cause congenital blindness, including certain diseases and genetic factors. Yet this latest discovery and subsequent hunt for the genetic mutation responsible for night blindness, may allow for the development of gene therapy to correct the dysfunction in people as well as dogs.
People with congenital stationary night blindness (CSNB) have normal vision during the day but find it difficult or, in some cases, impossible to distinguish objects in low light. This rare condition is present from birth and can impact the individual’s quality of life, especially in locations or in conditions where artificial illumination is not available.
Researchers at the University of Pennsylvania School of Veterinary Medicine worked with Japanese scientists whom had found out about a unique population of Beagles with night-vision problems. The dogs had been bred by a Japanese pharmaceutical company and displayed behaviours characteristic of night blindness. Dr Gustavo Aguirre, a Professor of Medical Genetics and Ophthalmology at the University of Pennsylvania and Director of the Inherited Eye Diseases Clinic, says of the project: “In bright light they can walk around and navigate easily, but in darkness they sort of freeze. It’s really very dramatic.”
The research team confirmed that the condition in the Beagles was CSNB by using physiological measures of the dogs’ retinal function using a technique called electroretinography. This involves using a flash of light and detecting what signals are coming from the photoreceptors and other cells of the retina. The team then vary the light intensities and create different dark and light adaptation situations to confirm the particular condition the dog may have.
All the affected dogs in this study showed signs that were characteristic of CSNB, specifically a type known as Schubert-Bornschein complete CSNB, which is also seen in humans. This is where there is a malfunction in the process by which signals are transmitted between the retina’s photoreceptor cells and bipolar cells. The Japanese investigators first evaluated the dogs’ pedigree to determine how the condition was inherited and found it was an autosomal recessive disease. This process also allowed the scientists to see which dog was a carrier for the disease.
The scientists found a distinct pattern between affected, carrier and normal individuals when they used protein markers that labelled the synaptic end of the photoreceptor cells. Affected dogs had reduced labelling compared to carriers which, in turn, had reduced labeling compared to the control dogs. “We often find with a disease where we have a loss of function that, even without a loss of cells, proteins and receptors may redistribute to different locations,” Aguirre said.
The gene responsible for these dogs’ condition remains a mystery, but the researchers believe a genome-wide approach by means of whole-genome sequencing will narrow their hunt. The scientists are excited about this possibility, as the gene may represent a novel one not previously associated with CSNB, and this will consequently help us in better understanding this condition in humans too.