A deadly mystery plagued the Manchester terrier breeding community for years. Puppies were dying suddenly despite every effort to ensure their parents were a healthy pairing. Breeders like Amanda Kelly, who has bred the toy variety of the terrier for nearly 35 years, were shattered by every loss.  

“As a breeder, we all set out to try to create the happiest, healthiest puppies that we possibly can,” she says. “To have an owner contact you because the dog that they love with all of their heart is ill is devastating. It's heartbreaking when you're a breeder, and you feel like you are powerless.”

Then, researchers at the University of Minnesota College of Veterinary Medicine (CVM) discovered answers. They identified a genetic variant linked to sudden cardiac death in the young (SCDY) in two related dog breeds—Manchester terriers and English toy terriers. 

This devastating event results from an inherited form of dilated cardiomyopathy—when the heart becomes weakened and enlarged, making it unable to function properly. These new findings have implications for predicting SCDY and dilated cardiomyopathy in humans, too.

In humans, SCDY often has a genetic basis, but because the condition is rare, it is difficult for researchers to amass enough data to confirm that specific genetic variants are the cause of disease. 

On the other hand, dog breeds that have undergone many generations of selective breeding have relatively little genetic diversity—including among genes that cause disease—making it far easier to identify variants linked to specific conditions. And because dogs share susceptibility genes for many inherited diseases with humans, including sudden cardiac death, canine models offer promising avenues for understanding the genetic basis of the condition in humans.

Manchester terriers provide one such model, and the researchers led by Dr. Eva Furrow, associate professor of internal medicine at CVM and co-director of the Minnesota Urolith Center, sought to identify the gene responsible for SCDY in the breed using a genome-wide association study. In this type of study, thousands of genetic markers are scanned to look for associations between the markers and disease. This allows researchers to pinpoint the location of disease-causing variants.

The study initially enrolled 48 Manchester terriers, including 12 dogs that had passed away suddenly before 2 years of age from SCDY and 36 healthy adult dogs. A follow-up phase to validate the findings added more dogs, including English toy terriers, a closely related breed, for a total of 26 cases of SCDY and 398 healthy adult dogs.

The researchers found a variant in a gene called ABCC9. Having two copies of this variant (i.e., one from each parent) had a perfect association with SCDY, supporting a causal role in the disease. 

The discovery was welcome news to Kelly and fellow breeders who had experienced decades of heartbreak. 

“When Dr. Furrow contacted us and said that she had found the gene for it, I sat in my office and cried because I spent 25 years trying to figure out how to breed dogs that wouldn't die,” Kelly says. “Every time you do a breeding, you're doing the very best that you can with the information that is available, but what we had at the time was imperfect information.” 

According to Furrow, this discovery would not have been possible without the support of Manchester terrier breeders, who contributed through research donations and by recruiting dogs to participate in the study. This support had a powerful impact. 

“We can now test Manchester terrier and English toy terrier dogs for this SCDY variant in order to help breeders prevent any pairings that could result in affected puppies,” Furrow says. “This testing has essentially eliminated the devastating situation where a seemingly healthy puppy dies from SCDY with no warning.” 

The discovery also advances human medicine. Each year, there are an estimated 3,400 sudden unexpected infant deaths (SUID) in the United States, according to the Centers for Disease Control and Prevention. These deaths have no immediately obvious cause and occur among infants 12 months old and younger. The American Academy of Pediatrics recognizes congenital cardiac conditions among potential causes of death in SUID cases. 

“Variants in ABCC9 have been identified in sudden infant death cases, but there were too few cases to be certain this gene plays a role in the disease,” Furrow says. “The findings of our study help confirm that ABCC9 is a susceptibility gene for SCDY and dilated cardiomyopathy, which ultimately helps clinicians diagnose these conditions and maybe one day work toward preventing them.”