Test Detail

Gallbladder Mucocele (GBM)

General · Dog

Dilatation of the gallbladder due to accumulation of abnormal mucus (mucin) that distends the wall and predisposes to rupture and biliary peritonitis. It is a multifactorial disease, with marked breed predisposition (Shetland Sheepdog, Cocker Spaniel, Pomeranian, Cairn Terrier, Miniature Schnauzer) and familial aggregation in some lines. The genetic component is unresolved: the candidate variant in ABCB4 (MDR3) was initially associated with risk, but the association was not replicated and was refuted; it must not be used as a diagnostic test.

Inheritance pattern	Multifactorial (polygenic + environmental/endocrine factors). The initial hypothesis of dominant inheritance with incomplete penetrance in the Shetland Sheepdog (Mealey 2010) was not confirmed; Cullen (2014) proposes multifactorial or non-hereditary inheritance.
Gene / Mutation	Candidate variant, NOT confirmed as causal: ABCB4 (MDR3) c.1660_1661insG p.(L554Rfs) —g.13584928_13584929insC (CanFam3.1), OMIA001524-9615—; published as ABCB4 1583_1584G. It inserts a guanine in exon 12 and generates a frameshift with premature termination. OMIA classifies it as "not evaluated" and advises against its use as a diagnostic marker, because the association with the mucocele was not replicated (Cullen et al. 2014). No causal variant has been identified in the other predisposed breeds.
Penetrance	Not applicable to a variant not confirmed as causal. Predisposition to the disease is multifactorial, with incomplete penetrance and dependent on endocrine factors (hypothyroidism, hyperadrenocorticism) and environmental factors (diet, hyperlipidaemia). The presence of the candidate variant does not predict the clinical development of mucocele.
Code	dfub
Turnaround time	15 days
Price	52,60 €

Incidence

Marked breed predisposition: Shetland Sheepdog (highest relative risk), Cocker Spaniel, Pomeranian, Cairn Terrier and Miniature Schnauzer. There are no reliable carrier frequencies in large series (limited data).

Breeder management

- There is no validated or useful genetic test for GBM; do not use ABCB4 c.1660_1661insG for selection purposes.
- Given the multifactorial nature, prioritise control of risk factors (thyroid, cortisol, weight, diet) and ultrasound monitoring in predisposed breeds.
- Do not breed animals with a clear clinical or familial history of GBM without individualised veterinary assessment.
- Avoid crosses between lines with repeated history, so as not to concentrate risk factors.

Specialist notes

Ultrasound diagnosis: heterogeneous biliary content without acoustic shadow ("kiwi"), thickened wall. Differentiate from cholecystitis and from an isolated mucus plug. Frequent comorbidities: hypothyroidism, hyperadrenocorticism and pancreatitis; always assess the endocrine and lipid profile. Cholecystectomy is indicated in symptomatic cases or those with an altered wall, not on a generalised prophylactic basis. The former ABCB4 molecular test has no clinical value.

References

1. Mealey KL et al. 2010. An insertion mutation in ABCB4 is associated with gallbladder mucocele formation in dogs. Comparative Hepatology. PMID: 20598156
2. Cullen JM et al. 2014. Lack of association of ABCB4 insertion mutation with gallbladder mucoceles in dogs. Journal of Veterinary Diagnostic Investigation. PMID: 24760133
3. Jaffey JA et al. 2019. Effect of clinical signs, endocrinopathies, timing of surgery, hyperlipidemia, and hyperbilirubinemia on outcome in dogs with gallbladder mucocele. The Veterinary Journal. PMID: 31492387
4. OMIA:001524-9615. Gallbladder mucoceles in Canis lupus familiaris. Online Mendelian Inheritance in Animals.

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