Congenital Idiopathic Megaesophagus Risk Factor (German Shepherd Type)

Other Names: CIM
Affected Genes: MCHR2
Inheritance: Autosomal Recessive
Mutation: chr12:58385362-58385394 (canFam4): TGGAATGATGAAGGAATTGGATCTCACACCTAG/-
Breed(s): German Shepherd Dog, Shiloh Shepherd, White Shepherd Dog

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Common Symptoms

Congenital idiopathic megaesophagus is an inherited gastrointestinal disease in dogs. In dogs with this condition, the normal movement of ingested food or water to the stomach is impaired resulting in an enlarged esophagus. Affected dogs regurgitate meals and water, suffer development deficiencies due to malnutrition, and can experience complications such as aspiration pneumonia. Signs are observed typically at 4 weeks of age coinciding with weaning. Many affected pups are euthanized due to complications, but some may survive with intensive life-long management. Among surviving dogs, a small percentage may spontaneously resolve by one year of age. Studies indicate males are more likely to develop clinical signs than females, but the precise cause of this sex predilection is uncertain.

Testing Tips

Genetic testing of the MCHR2 gene in dogs will reliably determine whether it is a genetic Carrier of congenital idiopathic megaesophagus. This disease is inherited in an Autosomal Recessive manner. This means that dogs must receive two copies of the mutated gene (one from each parent) to develop the disease. In general, carrier dogs do not have features of the disease but when bred with another carrier of the same Mutation, there is a risk of having affected pups. Each pup born to this pairing has a 25% chance of inheriting the disease and a 50% chance of inheriting one copy and being a carrier of the MCHR2 gene mutation. Reliable genetic testing is important for determining breeding practices. To eliminate this mutation from breeding lines and avoid the potential of producing affected pups, breeding of known carriers to each other is not recommended. Dogs that do not carry the mutation are not at increased risk of having affected pups.

There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait.


  • Bell SM, Evans JM, Evans KM, Tsai KL, Noorai RE, Famula TR, Holle DM, Clark LA. Congenital idiopathic megaesophagus in the German shepherd dog is a sex-differentiated trait and is associated with an intronic variable number tandem repeat in Melanin-Concentrating Hormone Receptor 2. PLoS Genet. 2022 Mar 10;18(3):e1010044. [PubMed: 35271580]