Cystinuria Type I - Newfoundland

Cystinuria is an inherited metabolic defect of amino acid transport in which cysteine, ornithine, lysine, and arginine are transported abnormally in kidneys and intestine. Normally cystine is filtered in renal glomerulus and then reabsorbed back to blood in tubules. This has an effect that only low concentration of cystine is found in urine. Dogs with cystinuria do not absorb cystine in kidney tubules therefore they have abnormally high urine concentrations of cystine. Cysine is not soluble in alkaline or neutral pH, therefore its excess in urine forms crystals that lead to formation of cystine stones in kidney or bladder. Affected dogs often have inflammation of urinary system and have increased risk for urinary blockage which leads to kidney failure, rupture of bladder and death if not treated immediately. The average age when first clinical symptoms are noted is 4.8 years, however in Newfoundland dogs uroliths causing clinical signs were evident as early as 4–6 months of age. Cystine, lysine, ornithine, and arginine levels in the urine of affected dogs were markedly increased, but were normal in obligate heterozygotes. In addition, renal clearance studies revealed normal cystine and dibasic amino acid reabsorption in the clinically normal relatives compared to failure of reabsorption (and even active cystine secretion) in affected Newfoundland dogs.

Inheritance: autosomal recessive

Mutation: SLC3A1 gene

Genetic test: The method used for testing is extremely accurate and allows complete differentiation between affected animals, carriers and healthy dogs. Testing can be done at any age.