Cystinuria in Dogs: Which Breeds Are at Risk and How DNA Testing Prevents Bladder Stones

Cystinuria causes painful bladder and kidney stones that can block the urinary tract — a life-threatening emergency, particularly in males. DNA testing completely prevents affected offspring when used before breeding.

Cystinuria is an inherited defect in amino acid transport in the kidneys. Normally, the kidneys filter and reabsorb amino acids including cystine (an amino acid) from the urine. In dogs with cystinuria, the transport system is defective — cystine accumulates in the urine and forms stones (cystine uroliths) in the bladder and kidney.

Why Cystine Stones Are Dangerous

Cystine is relatively insoluble in urine at normal pH levels. Accumulated cystine crystallizes and forms stones that:

• Cause bloody urine, straining, and painful urination
• Lodge in the urethra and cause urinary obstruction — a life-threatening emergency in male dogs
• Require emergency surgical removal if obstructing
• Recur throughout the dog's life without management

Male dogs are more severely affected than females because of their longer, narrower urethra — stone passage is much more likely to cause obstruction.

Breeds Affected and Genetic Variants

Multiple distinct cystinuria mutations have been identified in different breeds:

Type I-A (SLC3A1 gene mutation):

• Newfoundland — carrier frequency is very high; Newfoundland-specific mutation
• Autosomal recessive — two copies required for disease

Type II-A (SLC7A9 gene mutation):

• Labrador Retriever — low but present carrier frequency
• Autosomal recessive

Type II-B:

• Australian Cattle Dog and related breeds
• Autosomal recessive

Androgen-dependent cystinuria:

• Irish Terrier, Miniature Pinscher, English Bulldog, and others
• This form is sex-linked and testosterone-dependent — intact males are affected, while spayed/neutered dogs often show remission
• DNA tests are available for some breed-specific variants

Other breeds with documented or suspected cystinuria:

• Scottish Deerhound
• Basset Hound
• Mastiff and related breeds
• Bernese Mountain Dog

Inheritance

Most cystinuria variants are autosomal recessive:

For Newfoundlands specifically, cystinuria Type I-A carrier frequency is high enough that all breeding dogs should be tested. Carrier × Clear pairings are safe — no affected offspring.

DNA Testing

DNA testing is available from multiple laboratories for the known mutations:

• Paw Print Genetics
• Embark (includes some variants)
• Animal Genetics

Because multiple distinct mutations cause cystinuria in different breeds, ensure you are testing for the correct variant for your breed. A "Clear" result for one mutation does not rule out other mutations.

Management of Affected Dogs

Dogs with cystinuria can be managed with:

• Dietary modification (low-protein, low-methionine diet)
• Increased water intake to dilute urine
• Urinary alkalinization (keeping urine pH above 7.0 dissolves cystine more readily)
• D-penicillamine or tiopronin medications in some cases
• Surgical or minimally invasive stone removal when stones form

Management is lifelong. Neutering intact males with androgen-dependent cystinuria often dramatically reduces stone formation.

Summary

Cystinuria is an inherited amino acid transport defect causing cystine stone formation in the bladder and kidneys. Multiple genetic variants affect different breeds; Newfoundlands have particularly high carrier frequency for Type I-A. DNA testing is available and completely prevents affected offspring from Carrier × Clear pairings. Male dogs face higher risk of life-threatening urinary obstruction. All breeders in affected breeds should test breeding stock and disclose carrier status to puppy buyers.