Primary Hyperoxaluria Type 1 (PH1) Health Testing in Dogs

Primary Hyperoxaluria Type 1 (PH1) is a rare hereditary metabolic disorder primarily affecting the Coton de Tulear breed. It stems from a mutation in the AGXT gene, resulting in a deficiency of the liver enzyme alanine-glyoxylate aminotransferase (AGT). This enzyme is essential for breaking down glyoxylate safely. Its deficiency leads to an accumulation of oxalate that forms calcium oxalate crystals, especially in the kidneys, causing severe damage and potentially kidney failure.

In this guide, we’ll explain PH1’s causes and symptoms, how it is inherited, and the vital role of health testing, enabling responsible breeding and better management of affected dogs.

What is Primary Hyperoxaluria Type 1 (PH1)?

PH1 is one of three types of primary hyperoxaluria, responsible for about 80% of affected cases in dogs. The condition is caused by the AGXT gene mutation, producing insufficient levels of the AGT enzyme in the liver. Without this enzyme, oxalate accumulates as calcium oxalate crystals.

This accumulation damages the kidneys by forming crystals in the urine and tissue, leading to kidney failure. The disease is systemic, with calcium oxalate deposits possibly affecting eyes, bones, joints, and other tissues, worsening rapidly from an early age.

In the Coton de Tulear breed, PH1 symptoms typically begin within the first month of life, making it an early onset and serious condition that often results in premature death or euthanasia.

Which Dogs Are at Risk?

The Coton de Tulear breed is particularly predisposed to PH1, though the condition can theoretically occur in various breeds. The disease is not contagious; it is inherited genetically. Both male and female dogs are affected equally, usually manifesting symptoms shortly after birth or within the first few weeks.

How is PH1 Inherited?

PH1 is passed down through autosomal recessive inheritance. This means a puppy must inherit a copy of the defective gene from both parents to be affected.

Dogs can be:

• Clear: No copies of the mutation, will not develop or pass on PH1.
• Carrier: One copy of the mutation, healthy themselves but can pass the gene on.
• Affected: Two copies of the mutation, will develop PH1 and suffer its consequences.

The breeding combinations and expected litter outcomes are:

• Two clear dogs 1414 have clear puppies.
• Two affected dogs 1414 produce only affected puppies.
• Two carriers 1414 result in 25% affected, 50% carriers, 25% clear puppies.
• One clear and one affected parent 1414 yield 100% carrier puppies.
• One clear and one carrier parent 1414 yield 50% clear, 50% carriers.
• One carrier and one affected parent 1414 yield 50% affected, 50% carriers.

Recognising Signs and Symptoms of PH1

Early signs in affected puppies often include:

• Excessive thirst and urination
• Straining or difficulty when urinating
• Vomiting and lethargy
• Decreased urine production in advanced stages

Symptom onset is usually at 3-4 weeks of age. Without early intervention, the disease progresses rapidly, impacting vital organs and often resulting in kidney failure.

Health Testing for PH1 in Dogs

Testing is critical for diagnosis, management, and controlling the spread within the breed. Genetic testing is performed by taking a simple cheek swab or blood sample from your dog, which is sent to a specialised laboratory for analysis of the AGXT gene mutation.

Testing identifies whether a dog is clear, a carrier, or affected. Breeders are strongly advised to have their dogs tested before mating and to share results transparently with prospective puppy buyers. Responsible breeding decisions based on these tests help prevent affected litters.

Additionally, laboratory tests measuring oxalate levels in urine or blood can support diagnosis but genetic testing remains the gold standard for detection of PH1 status.

How to Get Your Dog Tested in the UK

Ask your vet for PH1 genetic testing for your Coton de Tulear or any dog suspected to be at risk. Many UK veterinary labs and specialised genetic testing companies provide this service, typically requiring only a cheek swab. Results usually return within a few weeks.

If you are considering buying a Coton de Tulear puppy, request to see health testing certificates for the parent dogs to ensure responsible breeding.

Breeders' Role in Controlling PH1

Responsible breeders use genetic testing results to make informed mating choices that avoid producing affected puppies. This sustainable approach increases the overall health of the breed and reduces the emotional and financial burden on owners and vets.

Conclusion

Primary Hyperoxaluria Type 1 (PH1) is a life-threatening inherited condition affecting puppies, especially in the Coton de Tulear breed. Understanding its genetic basis, recognising symptoms, and utilising health testing are essential steps toward managing this condition.

Early genetic testing enables breeders and owners to prevent affected litters, improve dog welfare, and foster responsible breeding. If you own or plan to acquire a Coton de Tulear puppy, make health testing part of your responsible ownership commitments.