US researchers have discovered a genetic variation associated with an often deadly esophageal disorder frequently found in German shepherd dogs.
German shepherds are predisposed to congenital idiopathic megaesophagus (CIM), an inherited disorder where a puppy develops an enlarged esophagus that fails to move food into their stomachs. Puppies with the condition regurgitate their food and fail to thrive, often leading to euthanasia.
While German shepherds have the highest incidence of the disease, other breeds are susceptible, too, including labrador retrievers, Great Danes, dachshunds and miniature schnauzers. Researchers do not yet know if the same genetic variation is involved in disease development in other breeds.
Now researchers from Clemson University, South Carolina, have identified the genetic cause and developed a genetic test for the disease that German shepherd dog breeders can use to reduce the risk that puppies in future litters will develop the disease, publishing their findings in PLOS Genetics.
CIM is often discovered when the puppies are weaned from the mother’s milk to solid foods at about four weeks of age.
“They don’t have swallowing activity,” first author Sarah Bell said.
“When the puppies swallow food, it just sits in their esophagus and doesn’t trigger those sequential contractions that normally occur to help push the food into the stomach.
“Because a dog’s esophagus is horizontal instead of vertical like ours, gravity doesn’t aid the transportation of food into the stomach.”
In the study, the team performed a genome-wide scan to identify genes associated with the disorder. The scan revealed an association on canine chromosome 12 and a variant within melanin-concentrating hormone receptor 2 (MCHR2), which affects appetite, weight and how food moves through the gastrointestinal tract. They believe that an imbalance of melanin-concentrating hormones plays a role in CIM.
The study also revealed that male puppies are twice as likely to be affected by the disorder than females. The researchers suspect that higher estrogen levels allow food to pass to the stomach more effectively, thereby protecting against disease development.
The MCHR2 variant, along with the dog’s sex, can predict whether a dog will develop a megaesophagus with 75 per cent accuracy. Owners can swab their dog’s gums and submit the sample to genetic testing companies to learn which variant(s) their dog inherited.