Gallbladder Mucoceles

Other Names: Hepatobiliary disease, Mucinous cholecystitis, Mucinous hyperplasia
Affected Genes: ABCB4
Inheritance: Autosomal Dominant With Incomplete Penetrance
Mutation: chr14:13584928-13584929 (canFam3): 1 bp insertion (ins G)

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Common Symptoms

Gallbladder Mucoceles are an inherited disorder of the liver affecting dogs. A mucocele is a gallbladder that is severely distended by mucus. It can result in inflammation (cholecystitis) and possible rupture of the gallbladder. Affected dogs usually present with vomiting, jaundice, loss of appetite and abdominal pain. If the gallbladder is not removed before rupture, the dog will become very painful and die. Though it is known that dogs inheriting one copy of the causal Mutation are at increased risk for this disease, the presentation of gallbladder mucoceles is variable between dogs and not all dogs inheriting a copy of the mutation will develop the disease. This suggests that there are environmental or other genetic factors responsible for modifying disease expression. Because gallbladder mucoceles have symptoms that are common to other diseases, it can be difficult to diagnosis without ultrasonography or surgery.

Breed-Specific Information for the Shetland Sheepdog

The Mutation of the ABCB4 gene associated with gallbladder mucoceles has been identified in Shetland Sheepdogs, although its overall frequency in this breed is unknown. The frequency of this disease and approximate age of disease onset are currently unreported for Shetland Sheepdogs though it is believed to be more common in older adult dogs. Based on the current scientific literature, more than one gene may be involved in expression of this disease in Shetland Sheepdogs. Therefore, not all Shetland Sheepdogs with gallbladder mucoceles will have one or two copies of this mutation. Due to Incomplete Penetrance, not all dogs with one or two copies of the mutation will develop gallbladder mucoceles. Currently, the mutation in ABCB4 is the only available molecular test for gallbladder mucoceles. Dogs testing negative for this mutation may still be at risk for gallbladder mucoceles based on pedigree or clinical history.

Testing Tips

Genetic testing of the ABCB4 gene in Shetland Sheepdogs will reliably determine whether a dog is a genetic Carrier of gallbladder mucoceles. Gallbladder Mucoceles due to Mutation of the ABCB4 gene are inherited in an Autosomal Dominant manner with Incomplete Penetrance meaning that dogs only need to inherit one copy of the mutated gene to be at an increased risk of developing the disease. Each pup that is born to an affected dog has a 50% chance of inheriting one copy of the ABCB4 gene mutation and being at-risk for the disease. Reliable genetic testing is important for determining breeding practices. Because symptoms do not appear until adulthood and because the mutation shows incomplete Penetrance, genetic testing should be performed before breeding. Until the exact modifying environmental or genetic factor is determined, genetic testing remains the only reliable way to detect disease associated with this mutation. In order to eliminate this mutation from breeding lines and to avoid the potential of producing affected pups, breeding of dogs known to have the mutation is not recommended. Shetland Sheepdogs that have not inherited the mutation have no increased risk of having affected pups. However, because there are other environmental and genetic factors associated with gallbladder mucoceles, a normal result in ABCB4 does not exclude gallbladder mucoceles in a pedigree.

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.

References

  • Aguirre AL, Center SA, Randolph JF, Yeager AE, Keegan AM, Harvey HJ, Erb HN. Gallbladder disease in Shetland Sheepdogs: 38 cases (1995-2005). J Am Vet Med Assoc. 2007 Jul 1; 231(1):79-88. [PubMed: 17605668]
  • Cullen JM, Willson CJ, Minch JD, Kimbrough CL, Mealey KL. Lack of association of ABCB4 insertion mutation with gallbladder mucoceles in dogs. J Vet Diagn Invest. 2014 Apr 23. [Epub ahead of print] [PubMed: 24760133]
  • Mealey KL, Minch JD, White SN, Snekvik KR, Mattoon JS. An insertion mutation in ABCB4 is associated with gallbladder mucocele formation in dogs. Comp Hepatol. 2010 Jul 3; 9:6. [PubMed: 20598156]
  • Pike FS, Berg J, King NW, Penninck D, Webster CR. Revision to gallbladder mucocele article. J Am Vet Med Assoc. 2004 Jun 15; 224(12):1916-7. [PubMed: 15230443]
  • Pike FS, Berg J, King NW, Penninck DG, Webster CR. Gallbladder mucocele in dogs: 30 cases (2000-2002). J Am Vet Med Assoc. 2004 May 15;224(10):1615-22. [PubMed: 15154731]