King Charles spaniels carry more harmful genes tied to heart problems than other dog breeds
UPPSALA, Sweden – King Charles Spaniels are an adorable and popular breed, especially among celebrity dog owners. Unfortunately, a new genetic study shows that this lovable breed is plagued by heart problems too. Researchers at Uppsala University say Cavalier King Charles Spaniels carry more harmful gene mutations than other breeds.
These mutations are the result of controversial selective breeding methods to maintain their cute traits. With his mild temperament, the Cavalier is the favorite animal of many families. However, the study notes that breeding practices have loaded them with disease-causing genetic variants. These include mutations related to MMVD (myxomatous mitral valve disease) – the most common congenital heart disease in dogs.
“We find that recent breeding may have accelerated the accumulation of harmful mutations in certain dog breeds,” says lead author Dr. Erik Axelsson in a statement to SWNS. “Especially in the Cavalier, one or more of these mutations affect the heart muscle protein NEBL and can make this breed susceptible to devastating heart disease.”
MMVD accounts for more than 70 percent of all canine heart disease cases. It is both a chronic and a progressive disease in puppies. The first signs are usually a heart murmur that develops after the age of six, experts say.
MMVD makes it difficult for dogs to breathe and move
The results show that the welfare and quality of life of many dogs have been seriously affected by selective breeding. Over hundreds of years it has created an incredible variety – with different sizes, shapes, and capabilities.
“Unfortunately, this process has also resulted in many breeds being more inbred and more likely to inherit genetic diseases,” says Dr. Axelsson opposite SWNS.
The Swedish team sequenced the complete genomes of 20 dogs from eight common breeds, from Beagles to German Shepherds and Golden Retrievers. They discovered that the Cavalier King Charles, who has seen the most intense breeding over the years, carries the most harmful mutations. The researchers also looked for certain variants in its DNA that are associated with MMVD – and identified two.
These genetic changes regulate a common protein in heart muscle known as NEBL and offers a possible explanation for the phenomenon. In dogs with this condition, one of the valves that control blood flow through the heart shrinks over time, reducing the amount pumped around the body. Dogs with MMVD may end up having difficulty breathing before they eventually die from the disease.
“The particularly large number of potentially harmful genes in the genome of Cavalier King Charles Spaniels compared to other dogs is probably due to its breeding history,” explains Dr. Axelsson.
The disadvantage of breeding dogs for appearance
Small dogs are more prone to life-threatening conditions caused by selective breeding. Historical records suggest that spaniel-type dogs have existed for at least 1,000 years. They were popular with kings all over Asia and Europe, including at the court of King Charles II from 1630 to 1685. The spaniels experienced several “bottlenecks” in which only a small part of their genes passed on to the next generation.
“They may have made the deleterious genes in the Cavalier King Charles Spaniel genome more abundant before the dog was recognized as a breed in 1945,” reports Dr. Axelsson.
Most dog breeds were originally chosen for specific purposes, such as hunting or guarding property. To win dog shows, owners these days breed pedigree dogs to highlight certain physical traits according to breed standards set by the Kennel Club. As a side effect of focusing on appearance breeding, there is a lack of genetic diversity – which increases the risk of hereditary 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 difficulty breathing and struggle with exercise.
In the case of the Cavalier King Charles Spaniel, they are also prone to syringomyelia, a painful condition in which the head is simply too small for the skull.
The results appear in the journal PLOS Genetics.
The South West News Service author, Mark Waghorn, contributed to this report.