Scientists have identified a gene that kills purebred dogs. Does it even matter?

Bull terrier owners might feel some relief when they learn that a team of international researchers has identified a genetic mutation behind the fatal acrodermatitis. Baby bull terriers with LAD do not grow well, have compromised immune systems, and develop skin lesions around their paws. They often die before their first birthday.

But here’s the thing: at this point, there’s not really much we can do about it.

The reason lies in the very first sentence of the article, which appeared in the newspaper on Thursday PLoS genetics. “Lethal acrodermatitis is a monogenic autosomal recessive genodermatosis in Bull Terriers and Miniature Bull Terriers,” the study states. This may not sound like much to you, but it means a lot to canine genetics researchers – that is, people who study canine genetics, not dogs who study genetics – because it immediately puts highlight why this disease is very similar to the vast majority of other diseases. that afflict purebred dogs. It’s autosomal, which means it can occur on any chromosome (not just the sex-determining ones), and it’s recessive, which means you need two copies for the disease manifests.

“About 70% of genetic diseases in dogs are autosomal recessive,” explains Carol Beuchat, scientific director of the Institute of Canine Biology. “And the reason is that a recessive mutation doesn’t hurt you if it’s not expressed, so it’s not selected against.” If everyone who carries a mutation suffers the associated ill effects, they will be less likely to reproduce and the mutation will not spread much through the gene pool. But recessive genes can proliferate more widely, because carriers with one copy can lead perfectly healthy lives and have many children, some of whom will also pass the recessive gene on to their own offspring.

A puppy with LAD between two of its littermates. Anina Bauer and her colleagues

“We all have dozens of recessive mutations that don’t matter unless we breed with someone else who has the same mutation,” Beuchat says. It may start to become more common in certain populations over time, with the recessive gene creeping into so many lineages that doubling becomes inevitable. But it’s more likely if you’re breeding with someone who shares much of the same genetic background. If you had children with your cousin, for example, you would be much more likely to have offspring with two copies of the same mutated gene because you share much of the same DNA. This is the whole principle of consanguinity. If you take a small population of closely related animals and breed them together, you end up accumulating recessive mutations. And boy oh boy do we have inbred dogs.

If two siblings have children together, they have what is called a 25% inbreeding coefficient. This means that their offspring are homozygous (have two copies of the same gene) for 25% of their DNA. About half of all dog breeds have an inbreeding coefficient greater than 25%. And the bull terriers? They are the second most inbred dog of all. Their coefficient is about 60%. Generation after generation has compounded the problem, that is, they have a higher and higher coefficient than pure siblings can produce.

So it’s not really surprising that the breed has accumulated a few genetic disadvantages along the way. Bull terriers are also prone to respiratory problems, heart and kidney disease, deafness, and knee problems.

Purebred dogs are all inbred because, well, that’s what it means to be a purebred dog. They must have parents who are registered as thoroughbreds, and their parents both had to be thoroughbreds, and so on until the Victorian era – when people decided that certain dogs would be considered bull terriers or German shepherds, wrote the names of each official pure breed in so-called pedigree books, and required owners to pay to register their dogs in the pure breed registry. In doing so, they unfortunately created a limited gene pool. Whatever genetic diversity there was in a breed 150 years ago became the upper limit of that gene pool, and we’ve been shrinking it ever since.

Many modern tactics for ensuring good canine health revolve around genetic testing and registries designed to identify which dogs are healthy and which are not. The goal: to breed only the healthy. But, as Jerry Klein, the American Kennel Club’s chief veterinarian, acknowledges, it’s not always that simple. “The simple fact of bringing together two dogs that are not dysplastic could result in a breed of dogs without dysplasia. But we may be introducing something else into the equation.

Of course, we all want dogs without hip dysplasia. But if you only breed dogs with good hips, you also narrow the gene pool considerably. You can completely eliminate hip dysplasia (probably not, but maybe), but since you’re taking the finite gene pool of a purebred and making it even smaller, you’ll likely end up with other disorders. genetics a few generations later. line . It’s just the genetic calculation talking.

“It’s really hard to get rid of the last copy of a recessive mutation,” says Beuchat. “The goal need not be to eliminate the gene from the gene pool. You need to make mutations rare.

bull terrier
A good boy. Little Monsters/Pixabay

In other words, the tools that identify and eliminate genetic mutations are actually doing the opposite of what they should be doing. They are shrinking the gene pool when they should be expanding it. Bull terriers already have an inbreeding coefficient of 60%, which means that these recessive mutations have already accumulated. They won’t magically disappear, and they certainly won’t disappear without causing a few more diseases to take their place. The only solution is to stop the inbreeding. Bull terriers will eventually die out as they become more and more inbred. Populations with finite gene pools simply do not survive. To save the race, it must be made impure.

There aren’t many breeders who want to do this, however. The Norwegian Lundehund is almost entirely extinct because it is so inbred, and yet the effort to save it by crossing it with other Norwegian dog varieties includes only a handful of breeders. Most lundehund owners adamantly refuse to allow their dogs to mate with anything other than another lundehund. It’s the same story with many other races.

The majority of Dobermans now succumb to the same heart disease. Bernese Mountain Dogs today have little hip dysplasia, but die from cancers that have become commonplace. There are a small number of people dedicated to the preservation of each breed through inbreeding or expanding the gene pool, most of whom meet informally outside of kennel clubs. But their efforts are generally not well regarded by their peers in the canine world.

It makes sense – people become breeders because they are attracted to a raise. It simply means that it is a very small minority that is willing to sacrifice some semblance of genetic purity for the survival of a race. Make no mistake: the mutts have the advantage.

Jeanetta J. Stewart