Study: a genetic test—and gender—predicts risk of canine CIM with 75% accuracy
Researchers at Clemson University have discovered a genetic variation associated with an often fatal esophageal disorder common in German shepherds—and developed a test to check for it, according to a new study.
Congenital idiopathic megaesophagus (CIM), is an inherited disorder where a puppy develops an enlarged esophagus that fails to move food into their stomachs. Puppies with this condition regurgitate their food and fail to thrive, often leading to euthanasia.
CIM generally manifests when the puppies are weaned from their mother’s milk to solid foods at about four weeks of age. The food just sits in their esophagus and doesn’t trigger the normal sequential contractions that help push food into the stomach.
“They don’t have swallowing activity,” said study author Sarah Bell, a graduate research assistant in genetics at Clemson. “Because a dog’s esophagus is horizontal instead of vertical like ours, gravity doesn’t aid the transportation of food into the stomach.”
Because gravity isn’t helping the process along, puppies with CIM have to eat and drink while sitting upright in a dog high chair—and stay there for up to 30 minutes afterward. Some will outgrow the condition, but many require lifelong symptomatic management that includes upright feedings, small liquid meals multiple times a day, gelatin cubes, and drug therapies.
A genome-wide scan of 936 German shepherds to identify genes associated with the disorder 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. The researchers believe that an imbalance of melanin-concentrating hormones plays a role in the disease.
The study also revealed that male puppies are twice as likely to be affected by the disorder than females, leading researchers to theorize that higher estrogen levels may allow food to pass to the stomach more efficiently in females, which could help keep CIM from developing.
In people, estrogen relaxes the sphincter that connects the esophagus to the stomach, so having more estrogen in the system means that sphincter is more likely to open naturally, easing movement of food into the stomach. Bell said that dogs with CIM who have taken sildenafil—the generic name for the active ingredient in Viagra, used to treat erectile dysfunction in human males—have shown good results because the drug relaxes the muscles that t connect the esophagus and stomach.
The researchers say sildenafil increases the percentage of dogs who outgrow CIM and no longer need to use a high chair when eating.
While CIM is most common in German shepherds, other breeds are susceptible, too, including Labrador retrievers, Great Danes, and dachshunds, although researchers don’t know yet if the same genetic variation plays a part.
The good news: the researchers say that the presence of the MCHR2 variant, in combination with a dog’s sex, has a 75% accuracy rate in predicting whether that dog will develop CIM.
Bell stressed that she always advocates not making a problem where there isn’t one when talking about breed-specific diseases: “If you’ve been breeding German shepherds for 20 years and you’ve never bred a [puppy with CIM], then don’t use this test,” she said. “But if you’re a breeder and you’ve had [CIM] puppies, you may benefit from the test.”
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