King Charles spaniel dog

(Photo by Steshka Willems from Pexels)

UPPSALA, Sweden — King Charles spaniels are an adorable and popular breed, especially with celebrity dog owners. Unfortunately, a new genetic study reveals this lovable breed is also plagued by heart problems. Researchers from Uppsala University say Cavalier King Charles spaniels carry more harmful gene mutations than other breeds.

Those mutations are the result of controversial selective breeding methods to preserve their cute features. Mild of temperament, the Cavalier is the pet of choice for many families. However, the study finds breeding practices have loaded them up with disease-causing genetic variants. They include mutations linked to MMVD (myxomatous mitral valve disease) – the most common congenital heart disorder in dogs.

“We find recent breeding may have led to an accelerated accumulation of harmful mutations in certain dog breeds,” says lead author Dr. Erik Axelsson in a statement to SWNS. “In the Cavalier specifically, one or several of these mutations affect heart muscle protein NEBL and may predispose this breed to devastating heart disease.”

MMVD accounts for more than 70 percent of all canine heart disease cases. It’s both a chronic and progressive disease in pups. Initial signs are usually a heart murmur that develops after the age of six, experts say.

MMVD makes breathing and exercise difficult for dogs

The findings add to evidence that the welfare and quality of life for many dogs has been seriously compromised by selective breeding. Over hundreds of years, it’s created an incredible diversity – with various sizes, shapes, and abilities.

“Unfortunately, this process has also caused many breeds to become more inbred and more likely to inherit genetic diseases,” Dr. Axelsson tells SWNS.

The Swedish team sequenced the full genomes of 20 dogs from eight common breeds, ranging from beagles to German shepherds and golden retrievers. They discovered the Cavalier King Charles, which has experienced the most intense breeding over the years, carries the largest number of harmful mutations. The researchers also looked for particular variants in its DNA linked to MMVD – and identified two.

These gene changes regulate a common protein in heart muscle known as NEBL, offering a potential explanation for the phenomenon. For dogs with this condition, one of the valves controlling blood flow through the heart shrivels over time, reducing the amount pumping through the body. Dogs with MMVD can end up struggling to breathe, before finally dying of the disease.

“The especially large number of potentially harmful genes in the genomes of cavalier King Charles spaniels, compared to other dogs, likely resulted from its breeding history,” Dr. Axelsson explains.

The downside of breeding dogs for appearance

Small dogs are more vulnerable to life-threatening conditions caused by selective breeding. Historical records suggest spaniel-type dogs have existed for at least 1,000 years. They were popular with royalty throughout Asia and Europe, including at the court of King Charles II from 1630 to 1685. The spaniels experienced several “bottlenecks” where only a small proportion passed on their genes to the next generation.

“They may have made the harmful genes more common in the cavalier King Charles spaniel genome before the dog achieved recognition as a breed in 1945,” Dr. Axelsson reports.

Most dog breeds were originally selected for particular purposes, such as hunting or guarding property. Nowadays, in order to win dog shows, owners breed pedigree dogs to emphasize certain physical features in accordance with breed standards set by the Kennel Club. As a side-effect of focusing on breeding for appearance, there’s a lack of genetic diversity – increasing the risk of inherited diseases.

Pugs, French bulldogs, and other similar types of “designer” dogs have short, flat faces and therefore often have narrow nostrils and abnormal windpipes. Scientists call flat-faced dogs brachycephalic. Many have breathing difficulties and struggle with exercise.

In the case of the Cavalier King Charles spaniel, they are also prone to Syringomyelia, a painful condition where the head is simply too small for the skull.

The findings appear in the journal PLOS Genetics.

South West News Service writer Mark Waghorn contributed to this report.

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