Primary hyperoxaluria type I is a rare but very serious inherited disease. It affects the metabolism, and it causes oxalate crystals to build up in the kidneys. In the Coton de Tulear, it is one of the most severe conditions a breeder can pass on, because affected puppies do not survive.
What causes it
The disease is caused by a mutation in the AGXT gene. This gene makes a liver enzyme that normally helps break down glyoxylate. When the enzyme does not work, glyoxylate turns into oxalate instead. The oxalate binds with calcium and forms crystals, mainly in the kidneys [citation:1][citation:3].
In the Coton de Tulear, the specific mutation is known: c.996G>A, which changes one amino acid (p.Gly102Ser) [citation:1][citation:3].
Signs in puppies
The disease shows up very early. Affected puppies usually become ill at three to four weeks of age, and some die within a week of the first signs [citation:3][citation:6].
Signs include:
- Vomiting and diarrhoea.
- Loss of appetite.
- Lethargy and depression.
- Drinking more and urinating more.
- Poor growth.
- Signs of sudden kidney failure.
Because the signs are similar to other puppy illnesses, the disease is often only confirmed after death, when a vet finds oxalate crystals in the kidneys [citation:1][citation:9].
Prognosis
The outlook is very poor. Most affected puppies are euthanised shortly after the signs appear, or they die on their own. There is no cure, and treatment is limited to supportive care, which is usually not enough [citation:1][citation:9].
How it is inherited
PH I is inherited in an autosomal recessive way [citation:1][citation:2]. A dog needs two copies of the mutation to be affected. A dog with one copy is a carrier. Carriers are healthy and show no signs, but they can pass the mutation to their puppies.
If two carriers are bred, each puppy has a 25 percent chance of being affected, a 50 percent chance of being a carrier, and a 25 percent chance of being clear [citation:8].
DNA testing
A DNA test is available. It uses a cheek swab or a blood sample and tells you whether a dog is clear, a carrier, or affected. The test can be done at any age, including on very young puppies [citation:14].
In a study of 118 Finnish Coton de Tulear dogs, about 8.5 percent were found to be carriers [citation:1][citation:6]. That number may vary in other countries, but it shows that the mutation is present in the breed and worth testing for.
Breeding advice
Because affected puppies do not survive, the only way to prevent the disease is to test before breeding. Two carriers should never be bred together. A carrier can be bred to a clear dog, but the puppies should be tested before they are used for breeding themselves [citation:1][citation:9].
If you are buying a puppy, ask the breeder whether the parents were tested for PH I and whether you can see the results.
What the club recommends in 2026
As of 2026, PH I DNA testing is part of the health screening the club encourages for breeding Cotons. It is a simple test that prevents a great deal of suffering. If you have questions about a test result, or you are not sure what it means for your dog, please write to us, call us, or come and visit us at a club event.
Sources: Société Centrale Canine, OMIA, Animal Genetics, Genomia, and the 2012 study by Vidgren et al. in Animal Genetics.
