Researchers uncover the genetic variant link to fatal esophageal disease in dogs

Researchers from Clemson University have found a genetic variation linked to a potentially fatal esophageal disease common in German shepherd dogs.

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Congenital idiopathic megaesophagus (CIM) is an inherited disorder in which a puppy develops an enlarged esophagus that does not allow food to pass into their stomachs. Puppies suffering from this illness vomit their food and do not survive, resulting in euthanasia.

While German shepherds have the most prevalence of the disease, additional breeds such as Labrador retrievers, dachshunds, Great Danes, and miniature schnauzers are also vulnerable. Researchers are unsure if the same genetic variation is associated with the development of sickness in other breeds.

Leigh Anne Clark, an associate professor in the Department of Genetics and Biochemistry, and her colleagues proposed a genetic test for the condition that German shepherd dog breeders may use to lower the likelihood of the disease developing in future puppies.

The findings were published on March 10^th, 2022, in the journal PLOS Genetics.

When pups are transitioned from their mother’s milk to solid meals at around four weeks of age, CIM is usually discovered.

They don’t have swallowing activity. 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.”

Sarah Bell, Study First Author and Graduate Research Assistant, Genetics, Clemson University

Puppies with megaesophagus should eat and drink while sitting upright in a dog highchair and stay there for 30 minutes to get water and food into their stomachs. Most of them will overcome the problem, while others will require lifetime symptomatic care, including upright feedings, little liquid meals many times a day, gelatin cubes, and medication therapy.

Clark and Bell used a genome-wide scan to find genes linked to the illness in their research. The scan indicated a link between a variation in the melanin-concentrating hormone receptor 2 (MCHR2) gene and hunger, weight, and how food travels through the gastrointestinal tract in dogs. Clark and her colleagues think that CIM is caused by an imbalance of melanin-concentrating hormones.

Male puppies are twice more likely as female puppies to be impacted by the condition, according to the study. Higher estrogen levels, according to the researchers, enable food to flow through the stomach more quickly, preventing illness development.

What they’ve found in people is that estrogen has the effect of relaxing the sphincter that connects the esophagus to the stomach. By having more estrogen, the smooth muscle there is naturally more likely to open. This increases the motility of food into the stomach. In dogs with megaesophagus disease, a drug called sildenafil has shown good results. What it does is to relax the sphincter that connects the esophagus and stomach.”

Sarah Bell, Study First Author and Graduate Research Assistant, Genetics, Clemson University

The active element in Viagra is known by the generic name sildenafil. According to Clark, sildenafil boosts the number of dogs that overcome the condition and no longer need to eat from a high chair.

With 75% accuracy, the MCHR2 variation, together with the dog’s sex, may forecast whether a dog will produce a megaesophagus. Homeowners can swab their dog’s gums and send the sample to a genetic testing company to find out which variant(s) their dog has inherited.

Breeders can utilize the test to limit illness incidence while maintaining genetic variety.

One thing I stress with any disease in any breed is don’t make a problem where there isn’t one. If you’ve been breeding German shepherds for 20 years and you’ve never bred a megaesophagus puppy, then don’t use this test. But if you’re a breeder and you’ve had megaesophagus puppies, you may benefit from the test.”

Sarah Bell, Study First Author and Graduate Research Assistant, Genetics, Clemson University