Primary Hyperoxaluria Type 1 (PH1) Genetic Testing in Dogs

Primary Hyperoxaluria Type 1 (PH1) is an uncommon inherited metabolic disorder that mainly affects the Coton de Tulear puppies. It is caused by a mutation in the AGXT gene, which results in a shortage of the liver enzyme called alanine-glyoxylate aminotransferase (AGT). This enzyme plays a crucial role in safely breaking down glyoxylate. When AGT is deficient, oxalate builds up and forms calcium oxalate crystals, predominantly in the kidneys, causing severe damage and possibly leading to kidney failure.

This article outlines the causes and symptoms of PH1, explains its genetic inheritance, and highlights the importance of health testing. This knowledge supports responsible breeding practices and improves management of affected dogs.

Understanding Primary Hyperoxaluria Type 1 (PH1)

PH1 is one of three known types of primary hyperoxaluria and accounts for approximately 80% of canine cases. The disorder arises from a mutation in the AGXT gene that results in insufficient production of the AGT enzyme in the liver. Without adequate AGT, oxalate accumulates as calcium oxalate crystals.

These crystals harm the kidneys by depositing in urine and tissues, often leading to kidney failure. Calcium oxalate deposits might also affect the eyes, bones, joints, and other tissue, worsening quickly even at a young age.

In Coton de Tulear dogs, symptoms usually appear within the first month of life. The early onset makes it a severe condition, often resulting in early death or euthanasia.

Breeds at Risk for PH1

The Coton de Tulear breed has a known predisposition to PH1, although the disorder could potentially affect other breeds. Importantly, PH1 is not contagious; it is inherited genetically. Both male and female dogs are equally susceptible, commonly showing symptoms shortly after birth or within weeks.

Genetic Inheritance of PH1

PH1 follows an autosomal recessive inheritance pattern. For a puppy to be affected, it must inherit a defective copy of the gene from each parent.

Puppies can fall into one of three genetic categories:

• Clear: Possess no copies of the mutated gene and will neither develop nor pass on PH1.
• Carrier: Carry one copy of the mutation; healthy themselves but can transmit the gene to offspring.
• Affected: Have two copies of the mutation and will develop PH1, suffering its effects.

Typical breeding outcomes include:

• Clear x Clear parents produce only clear puppies.
• Affected x Affected produce only affected puppies.
• Carrier x Carrier: about 25% affected, 50% carriers, 25% clear puppies.
• Clear x Affected: all puppies will be carriers.
• Clear x Carrier: about 50% clear, 50% carriers.
• Carrier x Affected: roughly 50% affected, 50% carriers.

Warning Signs and Symptoms of PH1

Puppies affected by PH1 commonly show early signs such as:

• Excessive drinking and urination
• Difficulty or straining while urinating
• Vomiting and fatigue
• Decreased urine output in later stages of the disease

Symptoms generally begin between 3 to 4 weeks old. Without prompt diagnosis and care, the disease advances quickly, damaging vital organs and often leading to kidney failure.

Genetic Health Testing for PH1 in the United States

Genetic testing is essential for diagnosing PH1, managing affected dogs, and preventing the condition's spread within breeds. In the U.S., testing is typically done by collecting a simple cheek swab or blood sample from the dog and sending it to specialized veterinary genetic laboratories for DNA analysis of the AGXT gene mutation.

This genetic test determines if a dog is clear, a carrier, or affected by PH1. American breeders are highly encouraged to test breeding dogs before mating and to disclose results openly to potential puppy buyers. These measures promote responsible breeding and significantly reduce producing affected litters.

Some established laboratories like Embark Veterinary and others offer PH1 testing either standalone or within broader canine genetic screening panels.

While laboratory tests measuring oxalate levels in urine or blood can assist in diagnosis, genetic testing remains the most accurate and reliable method to identify PH1 status.

Getting Your Dog Tested in the U.S.

If you own a Coton de Tulear or suspect your dog may be at risk, request PH1 genetic testing from your veterinarian. Numerous U.S. veterinary labs and commercial genetic testing companies provide this service, usually requiring only a cheek swab. Results typically come back within a few weeks.

Before purchasing a Coton de Tulear puppy, always ask for health clearances from the parents to ensure they have been responsibly tested, preventing the transmission of PH1.

The Role of Breeders in Reducing PH1 Cases

Responsible breeders leverage genetic test results to make informed mating choices that avoid producing affected puppies. This approach helps to gradually eliminate PH1 from the breeding population, improving the overall health and well-being of the breed and reducing emotional and financial hardship for families and veterinarians.

Summary

Primary Hyperoxaluria Type 1 (PH1) is a serious hereditary disease that mainly affects puppies of the Coton de Tulear breed. Understanding the genetic cause, recognizing early symptoms, and using health testing are vital to managing this condition effectively.

Early genetic screening enables breeders and owners to prevent the birth of affected puppies, enhancing welfare and supporting responsible breeding practices. If you own or plan to buy a Coton de Tulear puppy, incorporating health testing into your care routine is a crucial part of responsible pet ownership.