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Cavalier King Charles spaniels carry harmful genetic variants

Cavalier King Charles spaniels have an increased number of harmful genetic variants compared to other dogs, according to a new study published by PLOS. The researchers found that modern dog breeding practices are to blame for the disease-causing mutations, including variants linked to a dangerous heart condition.

“We find that recent breeding may have led to an accelerated accumulation of harmful mutations in certain dog breeds,” explained study lead author Erik Axelsson of Uppsala University. “In the cavalier King Charles spaniel specifically, one or several of these mutations affect heart muscle protein NEBL and may predispose this breed to devastating heart disease.”

Over the last 200 to 300 years, dogs have been bred in closed populations with the goal of reinforcing specific desirable traits. While this type of selective breeding can produce extraordinarily diverse dogs, it also leads to an increased rate of inbreeding within the closed populations. This results in the loss of genetic variation and randomly promotes individual disease mutations.

The researchers set out to investigate whether recent breeding practices have increased the number of risky genetic mutations in common dog breeds. The experts sequenced and analyzed the entire genomes of 20 dogs, including beagles, German shepherds, and golden retrievers. 

The study revealed that the cavalier King Charles Spaniel carried the most harmful genetic variants. The experts also noted that this group had experienced the most intense breeding.

The researchers also investigated which genetic variants may be linked to a common heart condition known as myxomatous mitral valve disease (MMVD). With this condition, the mitral valve in the heart degenerates and allows blood to leak from the left ventricle back into the left atrium.

The study pinpointed two genetic variants that are tied to MMVD. These variants appear to regulate a gene that codes for a common protein in heart muscle. According to the study authors, the results offer a potential explanation for why cavalier King Charles spaniels are predisposed to the disease.

“Our finding represents the first clear indication of a relative increase in levels of deleterious genetic variation in a specific breed, arguing that recent breeding practices probably were associated with an accumulation of genetic load in dogs,” wrote the study authors. 

The large number of potentially harmful genes identified in the genomes of cavalier King Charles spaniels seem to be the result of their long breeding history. There is evidence that small, spaniel-type dogs have existed for 1,000 years or longer. These particular dogs were popular at royal courts for several hundred years throughout Asia and Europe, including the court of King Charles II from 1630 to 1685.  

The study is published in the journal PLOS Genetics.

By Chrissy Sexton, Staff Writer

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