Canine Gallbladder Mucocele (GBM)
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 the recent years. Although gallbladder mucocele is primarily a canine disorder, it has been diagnosed also in cats and ferrets.
Characteristics and Symptoms
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 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, but which makes them also potentially cytotoxic. The presence of phospholipids, phosphatidylcholine play 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 translocation of the 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 the heterozygous dogs and their symptoms appear to be more severe. Since GBM symptoms do not need to appear in early ages of the dog and the disorder can be present for a long time before being identified, it is important to prevent breeding of dogs with mutated genes and obtaining affected cubs.