Developing DNA Test to Eliminate Inherited Blindness in English Shepherd Dogs

Researchers at Cambridge have discovered the genetic mutation that causes English Shepherd Dogs to suffer from progressive retinal atrophy, an irreversible form of blindness. They have also created a genetic test to help prevent the disease in future English Shepherd Dogs.

A class of hereditary disorders known as progressive retinal atrophy (PRA) results in a gradual deterioration of the light-sensitive cells in the back of the eye. At birth, dogs with PRA have normal vision, but by the time they are four or five years old, they will be completely blind.

A University of Cambridge-led team has discovered the genetic mutation that causes PRA in English Shepherd Dogs and created a test for it using DNA. This provides a tool to guide breeding decisions, preventing the disease from being passed on to puppies by identifying dogs carrying the disease before their eyesight begins to fail.

Most often, owners are unaware that their dog has PRA until the dog reaches middle age, at which point it may have mated and given the defective gene to its offspring. Because of this, the disease is challenging to manage.

Using this recent discovery, it is now possible to swiftly eradicate progressive retinal atrophy from the English Shepherd Dog population. The results Were published in the journal Genes.

Once the dog’s eyesight starts to fail, there’s no treatment – it will end up totally blind.”

Katherine Stanbury, Researcher and Study First Author, Department of Veterinary Medicine, University of Cambridge

She added: “Now we have a DNA test, there’s no reason another English Shepherd Dog ever needs to be born with this form of progressive retinal atrophy – it gives breeders a way of totally eliminating the disease.”

The team discovered that the genetic mutation is recessive, meaning that an English Shepherd Dog will only become blind if it inherits two copies of it. If only one copy exists, the dog is considered a carrier; although it will not develop PRA, it can pass the mutation on to its offspring. About one in four puppies produced from a breeding pair of carriers will have PRA.

Dogs are far more likely than humans to be afflicted by recessive diseases because dog breeds are highly inbred and have large family groups.

After receiving a call from a distressed owner of an English Shepherd dog that had just received a PRA diagnosis, the team set out to conduct research.

The dog, who had been used for search and rescue missions, was forced to retire because of visual degradation that left him completely blind. Following an appeal for DNA samples from other English Shepherd breed owners or breeders, the researchers received samples from six dogs with PRA and twenty without it. This was sufficient for them to use whole genome sequencing to identify the genetic mutation causing PRA.

The group provides dog breeders with DNA testing as part of a for-profit canine genetic testing service to help them prevent breeding dogs that will inherit diseases. As part of this, they will now provide a DNA test for Progressive Retinal Atrophy in English Shepherds. For just £48, anyone can purchase a testing kit that allows them to take a swab from their dog's mouth and send it back for analysis.

An owner won't necessarily notice their dog has got anything wrong with its eyes until it starts bumping into the furniture. Unlike humans who will speak up if their sight isn’t right, dogs just have to get on with things.”

Dr. Cathryn Mellersh, Study Senior Author, Department of Veterinary Medicine, University of Cambridge

Mellersh added: “For the price of a decent bag of dog food, people can now have their English Shepherd tested for Progressive Retinal Atrophy prior to breeding. It’s about prevention, rather than a cure, and it means a huge amount to the people who breed these dogs. They no longer need to worry about whether the puppies are going to be healthy or are going to develop this horrible disease in a few years’ time.”

A popular herding dog breed in the US, the English Shepherd is closely related to the Border Collie.

The team has discovered thirty-three genetic mutations that cause inherited diseases in dogs, twenty-three of which cause diseases of the eyes. This is a new discovery. They claim that many of them have compromised health and well-being due to how humans have bred dogs.

The English Shepherd Dog is one of the many dog breeds that suffer from PRA. Additionally, it resembles a condition that results in blindness in humans, known as retinitis pigmentosa. The researchers believe that by studying the disease in dogs, they may better understand the illness's human formand even pinpoint future gene therapy targets.