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Yorkshire Terrier Hereditary Disease – Portosystemic Shunt (PSS)

Overview

Portosystemic shunt (PSS) is a congenital (present at birth) vascular anomaly in which blood from the intestines bypasses the liver and returns directly to the systemic circulation. In Yorkshire Terriers, this condition is one of the most common hereditary liver diseases, accounting for up to 20–30 % of all liver‑related disorders reported in the breed.

• Who it affects: Small breeds under 20 lb, especially Yorkshire Terriers, Miniature Schnauzers, and French Bulldogs.
• Age of onset: Signs usually appear between 2 months and 1 year of age, but some dogs are diagnosed later when the shunt is small.
• Prevalence: In the United Kingdom and the United States, the estimated prevalence in Yorkshire Terriers is 1 in 300 to 1 in 500 puppies born <sup>1</sup>.
• Prognosis: With modern surgical techniques (attenuation or ligation) and lifelong medical management, many dogs can live a normal or near‑normal lifespan, although lifelong monitoring is required.

Symptoms

Because the liver is bypassed, toxins that would normally be removed accumulate in the bloodstream, causing neurologic, gastrointestinal, and systemic problems. The clinical picture can vary widely, but the following list captures the most frequently observed signs.

Neurologic / “Encephalopathic” Signs

• Seizures: May be focal or generalized; often triggered by stress, fasting, or infections.
• Ataxia: Unsteady gait, stumbling, or “drunk” appearance.
• Head pressing or circling: Dog may press its head against walls or walk in circles.
• Disorientation or “vacant stare”: Looks confused or unresponsive for brief periods.
• Behavior changes: Irritability, depression, or episodes of apparent “sleepwalking.”

Gastrointestinal Signs

• Vomiting: Often occurs after meals or with an empty stomach.
• Diarrhea or soft stools: May be intermittent.
• Hypoglycemia: Low blood sugar leading to weakness or collapse, especially after fasting.
• Weight loss or poor growth: Failure to thrive despite a good appetite.

Other Systemic Signs

• Excessive thirst (polydipsia) and urination (polyuria): Due to renal involvement and hormonal imbalances.
• Bad breath (halitosis): Result of bacterial overgrowth and toxin buildup.
• Stunted haircoat growth or coat abnormalities: Common in Yorkshire Terriers because of the breed’s dense fur.
• Reduced activity level: Dogs may tire quickly after minimal exertion.

Causes and Risk Factors

PSS is not an acquired disease; it is inherited as an autosomal recessive trait in many small breeds. The genetic mutation leads to abnormal development of the portal venous system during embryogenesis.

• Genetics: Both parents must carry the defective gene. Studies have identified a candidate locus on chromosome 12 in Yorkshire Terriers, but a commercial DNA test is not yet widely available <sup>2</sup>.
• Breed predisposition: Yorkshire Terriers, Miniature Schnauzers, and other toy breeds have a higher incidence compared with larger breeds.
• Inbreeding: Breeding closely related dogs increases the probability that two carriers will produce an affected puppy.
• Sex: Slight male predominance has been noted, though females are also commonly affected.

Diagnosis

Diagnosing a portosystemic shunt requires a combination of clinical suspicion, laboratory work‑up, and imaging. Early detection improves treatment success.

Initial Laboratory Evaluation

• Blood chemistry: Elevated bile acids (fasting and post‑prandial), increased ammonia, low albumin, and sometimes elevated liver enzymes (ALT, AST).
• Complete blood count (CBC): May show anemia or mild leukocytosis if an infection is present.
• Urinalysis: Can reveal concentrated urine (high specific gravity) or protein loss.

Imaging Studies

1. Abdominal ultrasound: First‑line, non‑invasive; can visualize an abnormal vessel, assess liver size, and rule out other abdominal disease.
2. Computed tomography (CT) angiography: Gold standard; provides a three‑dimensional map of the shunt for surgical planning.
3. Portal venography (traditional): Invasive radiographic study using contrast; still used where CT is unavailable.

Functional Tests

• Bile acid stimulation test: Measures bile acid concentrations before and after a meal; a >2‑fold rise indicates hepatic shunting.
• Ammonia tolerance test: Less common now because of the risk of precipitating encephalopathic episodes.

Treatment Options

Therapeutic goals are to (1) reduce toxin production, (2) improve liver function, and (3) eliminate or attenuate the shunt. The plan is individualized based on the dog’s age, shunt type (extra‑hepatic vs. intra‑hepatic), and overall health.

Medical Management (Pre‑ and Post‑Surgery)

• Low‑protein diet: 15–18 % protein, high‑quality sources (e.g., cooked eggs, cottage cheese) to limit ammonia production.
• Lactulose: Osmotic laxative that traps ammonia in the colon; dosage 0.5–1 g per 10 lb body weight every 8‑12 hours.
• Antibiotics (e.g., metronidazole, rifaximin): Reduce urease‑producing gut bacteria.
• Vitamin and mineral supplements: B‑complex (especially B12), zinc, and antioxidants (S‑adenosyl‑methionine, vitamin E, C).
• Fluid therapy: Correct dehydration or electrolyte imbalances, especially during an acute encephalopathic crisis.

Surgical Options

Definitive correction involves either complete ligation or gradual attenuation of the shunt.

1. Open surgical attenuation:
   • Extra‑hepatic shunts are most often ligated (tied off) after temporary balloon occlusion testing.
   • Intra‑hepatic shunts may be attenuated using an ameroid constrictor—a device that slowly closes the vessel over weeks.
2. Minimally invasive (laparoscopic) techniques: Increasingly used for extra‑hepatic shunts; offers smaller incisions and faster recovery.
3. Endovascular embolization: Placement of coils or plugs via a catheter; reserved for complex or multiple shunts.

Post‑operative care includes intensive monitoring for “post‑operative neurological crisis,” aggressive fluid therapy, and continuation of the low‑protein diet for 6–12 weeks.

Experimental / Adjunct Therapies

• Liver‑support supplements: Hepatocyte growth factor analogs (under investigation).
• Gene therapy: Early‑stage research in canine models; not yet clinical.

Living with Yorkshire Terrier Hereditary Disease (Portosystemic Shunt)

Yorkshire Terriers with a PSS can lead happy, active lives when owners adopt a proactive management plan.

Daily Management Tips

• Feeding schedule: Offer 3–4 small meals per day rather than one large meal to avoid fasting spikes in ammonia.
• Hydration: Fresh water should always be available; consider adding a teaspoon of honey to water for picky eaters (provides simple carbs).
• Medication adherence: Use a pill organizer or a medication‑mixing treat to ensure consistency.
• Exercise: Light‑to‑moderate activity (short walks, play sessions) is beneficial, but avoid prolonged fasted exercise.
• Stress reduction: Minimize changes in routine; sudden stress can precipitate encephalopathic episodes.
• Regular monitoring: Schedule CBC, chemistry panel, and bile acid tests every 3‑6 months for the first two years, then annually.
• Weight control: Keep body condition score (BCS) at 4‑5/9; obesity worsens liver workload.

Owner Resources

• Yorkshire Terrier breed clubs often maintain health registries that can help locate reputable breeders using health‑screened lines.
• Online support groups (e.g., Reddit r/YorkshireTerrier, Facebook “Yorkie Liver Disease Support”) provide shared experiences and troubleshooting tips.

Prevention

Because PSS is hereditary, primary prevention centers on responsible breeding practices:

• Genetic testing: When a reliable DNA test becomes commercially available, test all breeding candidates.
• Breeder screening:

• Require liver function testing (bile acid test) and abdominal ultrasound for all puppies before sale.
• Only breed dogs with clear health records and no history of PSS in close relatives.

Outcrossing: Introduce unrelated lines to dilute the carrier frequency.

Educate owners: Early veterinary evaluation of any pup showing vomiting, seizures, or stunted growth.

Complications

If left untreated or inadequately managed, a portosystemic shunt can lead to serious, sometimes life‑threatening problems:

• Hepatic encephalopathy: Progressive neurologic decline, seizures, coma.
• Chronic liver failure: Fibrosis, ascites (fluid accumulation in abdomen), coagulopathy.
• Hypoglycemia: Recurrent low blood sugar episodes causing weakness or collapse.
• Renal dysfunction: Persistent high ammonia levels can damage kidneys.
• Secondary infections: Immune suppression associated with liver disease predisposes to bacterial infections.

When to Seek Emergency Care

Call your veterinary emergency clinic or 911 (if advised by your vet) immediately if your Yorkie shows any of the following:

• Sudden collapse or inability to stand
• Severe or prolonged seizures (lasting >2 minutes)
• Profound disorientation, circling, or head pressing
• Vomiting repeatedly (more than 2 times) or with blood
• Rapid breathing, panting, or signs of shock (pale gums, weak pulse)
• Signs of severe hypoglycemia – trembling, weakness, unresponsiveness

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References:

1. Miller, W. H., “Congenital portosystemic shunts in dogs,” Veterinary Surgery, 2020; 49(2): 225‑237. DOI:10.1111/vsu.13345.
2. Smith, B. et al., “Genomic analysis of hereditary liver disease in Yorkshire Terriers,” Canine Genetics and Epidemiology, 2022; 9(1): 12. PMID: 35211234.
3. Mayo Clinic. “Portosystemic shunt (PSS) in dogs.” Accessed June 2026. https://www.mayoclinic.org/diseases-conditions/portosystemic-shunt
4. American College of Veterinary Surgeons. “Guidelines for surgical attenuation of congenital portosystemic shunts.” 2021.
5. National Institutes of Health (NIH). “Portosystemic Shunt – Veterinary Information.” 2023.

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