Study finds dog breed with the most genetic variants that cause disease

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The King Charles Cavalier Spaniel is the breed of dog that carries the most disease-causing genetic mutations, a new study finds.

The small but lovable breed has been negatively affected by years of inbreeding, putting it at a higher risk of heart disease, the study warns.

Specifically, he exhibits genetic variants linked to myxomatous mitral valve disease (MMVD), a common and fatal heart disease.

The last 300 years of dog breeding have created an incredible diversity of breeds with varying sizes, shapes and abilities, say the authors.

But unfortunately, this has also caused many breeds to become more inbred and more likely to inherit genetic diseases.

King Charles I and his son Charles II were both passionate about the breed. The particularly high number of potentially harmful genes in the genomes of Cavalier King Charles Spaniels, compared to other dogs, is likely a result of their breeding history

Erik Axelsson from Uppsala University in Sweden and his colleagues today published the new findings in the journal PLOS Genetics.

“We find that individuals belonging to the breed affected by the most intense breeding – the Cavalier King Charles spaniel (cKC) – carry more harmful variants than other breeds,” they state in their article.

[This indicates] that past breeding practices may have increased overall levels of harmful genetic variation in dogs.

THE EIGHT BREEDS

1. Cavalier King Charles Spaniel

2. Beagle

3. German Shepherd

4. Golden retriever

5. Labrador retriever

6. Standard poodle

7. Rottweiler

8. West Highland White Terrier

(Note: breeds are not listed in order of genetic mutations, although the Cavalier King Charles spaniel was affected the most.)

Researchers in the study wanted to know if recent breeding practices had increased the number of disease-causing variants in dogs.

They sequenced the entire genomes of 20 dogs of eight common breeds, including the Beagle, German Shepherd, Golden Retriever, and Standard Poodle.

They found that the Cavalier King Charles Spaniel, which experienced the most intense breeding, carried genetic variants that were more harmful than the rest.

Standard Poodles were also found to carry more harmful mutations than many of the other breeds, but not as many as the Cavalier King Charles spaniel.

“We don’t see any significant difference between pairs involving these six breeds – beagle, German shepherd, golden retriever, Labrador retriever, Rottweiler, and West Highland white terrier,” Axelsson told MailOnline.

“They appear to have approximately similar levels and cannot be ordered.”

Next, comparisons of Dachshunds with and without signs of heart disease were then used to help identify mutations that potentially predispose Cavalier King Charles Spaniels to developing MMVD.

Axelsson and his colleagues chose to compare dachshunds to Cavalier King Charles Spaniels because dachshunds do not develop MMVD very frequently.

MMVD is caused when the mitral valve of the heart degenerates, allowing blood to flow from the left ventricle into the left atrium.

Researchers have identified two genetic variants linked to the disease, which appear to regulate a gene that codes for a protein common in heart muscle, called NEBL.

“We find that recent breeding may have led to an accelerated buildup of harmful mutations in some dog breeds,” Axelsson said.

Comparisons of dachshunds (right) with and without signs of heart disease were used to help identify mutations that potentially predispose Cavalier King Charles Spaniels to developing MMVD

Comparisons of dachshunds (right) with and without signs of heart disease were used to help identify mutations that potentially predispose Cavalier King Charles Spaniels to developing MMVD

“In the Cavalier King Charles Spaniel in particular, one or more of these mutations affect the heart muscle protein NEBL and may predispose this breed to devastating heart disease.”

While the breed’s predisposition to the disease is already known compared to other dogs, the new findings offer a potential explanation for why.

Portrait of King Charles II, who was passionate about the breed

Portrait of King Charles II, who was passionate about the breed

Axelsson told MailOnline that due to the small number of breeds examined – only eight – it is likely that there are several other breeds that carry similar amounts of potentially harmful mutations as do horsemen.

“Future research will likely answer this question and potentially provide a more specific answer as to why we are seeing these differences,” he said.

The particularly high number of potentially harmful genes in the genomes of Cavalier King Charles Spaniels, compared to other dogs, is likely a result of their breeding history.

Records suggest that small spaniel-type dogs have been around for at least 1,000 years and were popular in royal courts for several hundred years in Asia and Europe, including at the court of King Charles II (1630-1685) .

These spaniels experienced several “bottlenecks” where only a small percentage of the population passed their genes on to the next generation.

These bottlenecks may have made harmful genes more common in the Cavalier King Charles Spaniel genome before the dog was recognized as a breed in 1945.

Both King Charles I and his son Charles II were passionate about the breed, as the American Kennel Club (AKC) explains.

“Charles II was so attached to his spaniels that they accompanied him everywhere,” says the AKC on its website.

“He issued a royal decree that dogs should be allowed in all public spaces, including Parliament. The breed was even named for the monarch.

MEET THE KING RIDER CHARLES SPANIEL

The King Charles Cavalier Spaniel is a small spaniel with a short but defined muzzle, large brown eyes, and silky fur.

Its colors are black and tan, ruby, red and white (Blenheim) and tricolor (brown marking on a pearly white background).

Adults are 11.8-13 inches (30-33cm) tall and weigh 5.5-8kg.

The original Cavalier King Charles Spaniel dog breed was developed from the toy spaniels depicted in the work of 16th, 17th and 18th century painters such as Titian and Gainsborough.

They were very common as a pet for women and were used to warm the knees.

King Charles II loved his spaniels so much that he could not part with them.

By 1800, the snub-nosed variety had gained popularity and the original spaniel was almost lost.

Only the Duke of Marlborough kept a lineage alive, raising them to Blenheim Castle.

Read more: Purina


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