Clemson Canine Genetics
Megaesophagus is a disorder in which the esophagus dilates, or expands, to the point that the affected dog has trouble swallowing food and water. One of the major symptoms is regurgitation, which is the discharge of food and water from the pharynx or esophagus. This is different from vomiting, which involves the powerful, reflexive discharge of contents from the stomach. Dogs with megaesophagus will regurgitate both food and water that they have ingested.
Megaesophagus is seen in both dogs and cats, but is more commonly found in dogs. Several breeds of dog have been shown to have a hereditary link or susceptibility to megaesophagus. These breeds include the Wire-Haired Fox Terrier, the Miniature Schnauzer, the Great Dane, the Irish Setter, and the German Shepherd Dog.
Types of Megaesophagus:
Secondary/Acquired megaesophagus develops after the dog has reached maturity. This type occurs along with another disorder, injury, or other trigger; therefore, the cause of this type of megaesophagus can usually be determined by diagnosing the primary ailment. This type of megaesophagus can be a consequence of conditions that result in interference with either the esophageal muscles? function and/or the neural reflex that controls swallowing. In addition, diseases that affect the muscles of the esophagus and/or diseases that disturb peristalsis in the esophagus can lead to secondary/acquired megaesophagus. There also are several, more specific, diseases which have been noted as causing secondary/acquired megaesophagus, including myasthenia gravis, diseases of the central nervous system, polymyositis, peripheral neuropathies, esophagitis, and esophageal neoplasia.
Adult-onset idiopathic megaesophagus does not have a known cause, and the disorder manifests after the dog has matured. Congenital idiopathic megaesophagus (CIM) also does not have a known cause, but the symptoms present either while the dog is being weaned or soon thereafter. While the exact causes of idiopathic megaesophagus are not known, some authors have observed that dogs with idiopathic megaesophagus had three ?motor abnormalities?: 1) some region of the upper and/or middle of the esophagus did not have ?motor activity?; 2) the amplitude of the esophageal contractions was lower than that seen in unaffected dogs; and 3) after swallowing, there was an infrequent motor response of the esophageal body. As these authors indicated in their work, there are several conclusions that can be drawn from these results. First, CIM may occur in affected puppies because the muscles and nerves of the esophagus have not yet matured. Second, if this is the case, the development of these muscles and nerves as the puppies grow would explain the improvement seen in many of these dogs. Lastly, they found that a possible therapy for megaesophagus is cholinomimetic drugs.
The most definitive diagnosis of megaesophagus comes from thoracic radiographs and/or barium-swallow esophagrams of the dog in question, which are used to determine dilation of the esophagus.
Our lab has been working with dogs affected by congenital idiopathic megaesophagus, currently focusing our efforts on German Shepherd Dogs. We use a few methods for our research ? microarrays, polymerase chain reaction (PCR) as well as gene sequencing and sequence analysis. These methods allow us to study specific regions of chromosomes ? in our case, canine chromosomes. Thus far, we have found a significant association between the megaesophagus phenotype in German Shepherd Dogs and a region of chromosome 12 in the dog. This finding has led us to more closely examine this region of chromosome 12 in order to determine a haplotype that is shared by all dogs with megaesophagus in our study.
We are also comparing our results from affected German Shepherd Dogs with results from affected dogs of other breeds. This will allow us to further refine our haplotype and eventually determine the gene(s) involved in the megaesophagus phenotype we see in German Shepherd Dogs. While much has been found about this disorder by both our lab and others, there are still many questions left unanswered. We still need to find the specific gene or genes involved in this disorder ? genes that either cause this disorder or confer susceptibility to this disorder.
Currently, we are continuing to collect DNA samples from German Shepherd Dogs as well as dogs of other breeds that have been diagnosed with megaesophagus before one year of age. While we currently believe that the inheritance pattern of CIM in German Shepherd Dogs is complex, our work will hopefully allow us to determine both the true mode of inheritance and the specific genes involved in this disorder.
“Bubba” using elevated feeding and Doc Roy enzyme with bile added to his food. Feeding a Dog With Megaesophagus
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Guildford, WG. (1990) Megaesophagus in the Dog and Cat. Seminars in Veterinary Medicine and Surgery (Small Animal) 5:37-45. PMID:2191392
Hopper K, Beck, C and Slocombe, RF (2001) Megaoesophagus in adult dogs secondary to Australian tiger snake envenomation. Aust Vet J 79:672-675. PMID:11712704