Hereditary metabolic disease of the Coton de Tulear caused by a mutation in the AGXT gene, which encodes hepatic alanine-glyoxylate aminotransferase. The enzyme defect prevents the conversion of glyoxylate into glycine, so glyoxylate is transformed into oxalate, which precipitates as calcium oxalate crystals in the renal parenchyma. It causes acute tubular necrosis with fatal renal failure in puppies a few weeks old. It is the canine equivalent of human primary hyperoxaluria type I.

Affected breed: Coton de Tulear. The carrier frequency in the original Finnish study (of 118 dogs analysed) was 8.5%. No large series have been published in other populations of the breed; consider that the frequency may vary geographically.

- Sudden stunted growth at 3-4 weeks of life\n- Anorexia, depression, dehydration and vomiting\n- Oliguria or anuria due to acute tubular necrosis\n- Acute renal failure with elevated urea and creatinine\n- Crystalluria and massive deposition of calcium oxalate crystals in the kidney\n- Death within days to a few weeks after onset

Primary hyperoxaluria is one of the most classic congenital diseases of human genetics. In the dog, Vidgren and colleagues described in 2012 seven Coton de Tulear puppies from Finland belonging to four supposedly unrelated litters, all with a picture of sudden disease at 3-4 weeks of life and necropsy showing abundant deposition of oxalate crystals in renal tubules. Segregation analysis with microsatellites flanking AGXT and GRHPR pointed to AGXT as the candidate gene; sequencing of its exons revealed a single base change, c.996G>A, which changes a conserved glycine to serine (p.Gly102Ser). The study of 118 Finnish Coton de Tulear detected 10 carriers (8.5%), which confirms the variant as responsible and supports genetic screening before breeding.

- Test Coton de Tulear breeding dogs with the AGXT test before the first mating\n- Do not cross two carriers: 25% risk of fatal affected homozygotes in each litter\n- A carrier may be crossed with a clear animal; offspring intended for breeding must be tested and the clear ones preferably selected\n- In a litter with several puppies dead at 3-4 weeks with renal failure, suspect hyperoxaluria, confirm by necropsy with polarised light and genetic test, and do not repeat the parental cross\n- Exclude affected homozygous animals from breeding (they usually do not survive, but if they do, they must not breed)\n- Communicate the status to the buyer and record the result in the pedigree

Differential diagnosis with other causes of acute renal failure in puppies (renal dysplasia, polycystic kidney, leptospirosis, nephrotoxic agents, obstructive urolithiasis) and with calcium oxalate urolithiasis of the adult dog, which is usually multifactorial. The decisive finding: abundant calcium oxalate crystals in the renal parenchyma of a young puppy, with polarised light at necropsy. Do not confuse with hyperoxaluria of the Tibetan spaniel (described histological case, molecular basis not clarified). Symptomatic treatment (dialysis, fluid therapy) is usually insufficient; the prognosis is poor. Pre-breeding genetic testing is the essential preventive tool.

1. Vidgren G, Vainio-Siukola K, Honkasalo S, et al. Primary hyperoxaluria in Coton de Tulear. Anim Genet 2012;43(3):356-61. PMID: 22486513
2. OMIA:001672-9615 (AGXT). https://omia.org/OMIA001672/9615/