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Canine Gallbladder Mucocele
| Acronym: | GBM |
| Gene: | ABCB4 |
| Mutation: | 1583_1584 insG |
| Inheritance: | Autosomal dominant with incomplete penetrance |
| Sample type: | CHS (Cheek Swab), WBE (Whole Blood EDTA) |
Genetics and characteristics
Canine Gallbladder Mucocele (GBM) is a hepatobiliary disease in dogs characterized by progressive accumulation of mucus, resulting in variable degrees of bile duct obstruction. A mutation in the canine ABCB4 gene has been associated with GBM in Shetland sheepdogs, Cairn Terrier, Cocker Spaniel, and Pomeranian. Another known affected breed is the Miniature Schnauzer. There has been marked a high increase in the number of GBM-affected dogs in recent years. Although gallbladder mucocele is primarily a canine disorder, it has been diagnosed also in cats and ferrets.
The gallbladder is an organ where bile is stored and concentrated before it is released into the small intestine. Bile or gall is a dark green to the yellowish-brown fluid that aids in the digestion of lipids. It is composed of water, bile salts, bilirubin, and inorganic salts. Bile salts make an important compound of the bile, due to their detergent characteristics, which makes them also potentially cytotoxic. The presence of phospholipids and phosphatidylcholine plays an important role in protecting the epithelial cell membrane and decreasing the cytotoxicity of the bile salts. Thus, a decrease in the amount of biliary phosphatidyl-choline leads to injury of epithelial cells lining the biliary system. Symptoms include decreased appetite, anorexia, lethargy, vomiting, diarrhea, a yellowish tinge to the skin or gums, and abdominal pain. Progressive accumulation of mucus may cause a progressive increase in intraluminal pressure, necrosis of the gallbladder wall, gallbladder rupture, and its information. Affected dogs usually have increased liver enzyme activities and hyperbilirubinemia, as well as leukocytosis. Diagnosis of canine gallbladder mucocele can be confirmed by ultrasound.
in Shetland Sheepdogs is caused by the ABCB4 insertion mutation. ABCB4 is a phospholipid translocator, and it participates in the translocation of phosphatidylcholine. Properly functioning ABCB4 is essential for hepatobiliary homeostasis. The mutation results in a protein truncation that eliminates more than 50% of the protein. Canine Gallbladder Mucocele (GBM) is inherited as an autosomal dominant disorder and both homozygous and heterozygous for the mutation dogs will develop symptoms. Homozygous dogs appear to develop symptoms earlier than heterozygous dogs and their symptoms appear to be more severe. Since GBM symptoms do not need to appear at an early age in the dog and the disorder can be present for a long time before being identified, it is important to prevent the breeding of dogs with mutated genes and obtaining affected cubs.
Results Reported As
Test Result |
Interpretation of test result |
CLEAR |
Tested mutation was not detected in animal with „clear“ result. Animal tested as clear has wild-type allele in homozygous state (i.e. two pairs of healthy alleles). It will not develop disease caused by tested mutation.* It will pass only wild-type allele to its offspring. |
AFFECTED HETEROZYGOTE |
Tested mutation was detected in animal with „affected heterozygote“ result. Animal tested as affected heterozygote has one wild-type and one mutation allele, it is in heterozygous state. It is likely to develop disease caused by tested mutation.* It can pass wild-type or mutation allele to its offspring. |
AFFECTED |
Tested mutation was detected in animal with „affected“ result. Animal tested as affected has two copies of mutation alleles affecting the gene. It is likely the animal will experience a genetic disorder due to this mutation.** It will pass only mutation allele to its offspring. |
*Test excludes only tested mutation but not possible unknown mutations or factors that can lead to similar condition/symptoms.
**Penetrance of tested mutation, and potential unknown mutations or multiple other factors can possibly affect the likelihood of experiencing a genetic disorder.
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.
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.