Some dogs need to eat from a high chair or, more specifically, a Bailey chair. The chair keeps them upright while they eat so gravity can do the job their body can’t: move food from the mouth to the stomach.
These dogs have megaesophagus, a disorder of the esophagus that can prevent dogs from properly digesting food and absorbing nutrients. When you swallow a bite of food, it travels through a muscular tube, the esophagus, to the stomach. In humans, the esophagus is vertical, so our esophageal muscles don’t have to fight gravity. But because dogs are quadrupedal, a dog’s esophagus is more horizontal, so “there is a greater burden on the peristaltic contractions to transport food into the stomach.” In dogs with megaesophagus, the esophagus is dilated and these contractions are less effective. Instead of moving through the stomach properly, food can stay in the esophagus, making the problem worse and preventing proper digestion and nutrient absorption.
Leigh Anne Clark, Ph.D., associate professor at Clemson University, recently spoke to Duke about the megaesophagus in dogs and its genetic basis. She is the author of dozens of publications on canine genetics, including five cover articles. His research mainly focuses on[mapping] alleles and genes that underlie disease in dogs. In complex diseases like megaesophagus, this is easier said than done. “This disease has a spectrum,” Clark says, and “Spoiler: it makes it harder to map.”
Clinical signs of megaesophagus, or mega for short, include regurgitation, coughing, loss of appetite, and weight loss. (We could use the word “symptom” to talk about human conditions, but “a symptom is something someone describes, for example, I feel nauseous. But dogs can’t talk, so we can only see “clinical signs”) Complications of mega can include aspiration pneumonia and, in severe cases, gastroesophageal intussusception, an emergency in which dogs “suck their stomach into their esophagus.”
Sometimes megaesophagus resolves on its own with age, but when it does not, it requires lifelong management. Mega has no cure, but management may involve vertical eating, smaller, more frequent meals, soft foods, and sometimes medication. Even liquid water can cause problems, which is why some dogs with mega are given ‘water cubes’, made by adding a ‘gelatinous material’ to the water, instead of a bowl of water. regular water.
In dogs, mega can be either congenital, i.e. present at birth, or acquired. In cases of acquired megaesophagus, the condition is “usually secondary to something else”, and the root cause is often never determined. (Humans can also go mega, but like acquired mega in dogs, mega in humans is usually caused by a pre-existing condition. The best human comparison, Clark says, might be achalasia, a rare disease that causes difficulty swallowing.) Current research is looking at the congenital form of the disease in dogs.
His lab recently published a paper on the genetic basis of mega. Unlike some diseases, mega isn’t caused by a single genetic mutation, so figuring out which genes might be at play required some genetic detective work. “You see mega across races,” Clark says, suggesting an environmental component, but the disease is more prevalent in some races than others. For example, 28% of all diagnoses are of German Shepherds. It was a “red flag” indicating that genes were at least partly responsible.
Clark and his collaborators chose to limit their research study to German Shepherds. Despite including a wide range of dogs in the study, they noticed that males were significantly overrepresented. Clark thinks that estrogen, a hormone more abundant in women, may have a protective effect against mega.
Clark and his team performed a genome-wide association study (GWAS) to search for the most common alleles in dogs with mega. One allele that turned out to be a major risk factor was a variant of the MCHR2 gene, which plays a role in eating behaviors. In breeds where the mega is overrepresented, like German Shepherds, “we have a situation where the predominant allele in the population is also the allele at risk,” Clark says.
Using the results of the study, they developed a test that can identify a given dog’s version of the gene. The test, available from veterinary testing companies, is designed “to help breeders reduce the frequency of the at-risk allele and plan matings that are less likely to produce affected puppies.”
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