Genetic basis of Cystinuria - in the Newfoundland it is an autosomal recessive inherited disorder. Affected dogs inherit two abnormal copies of the gene (one from each parent) responsible for defects in the renal tubular reabsorption of certain amino acids, particularly cystine. While the condition occurs in multiple dog breeds, the Newfoundland type is more severe, with early onset and equal sex prevalence (unlike most breeds, where males are affected more often).
Pathophysiology - The defective gene disrupts the function of transport proteins in the kidney tubules responsible for reabsorbing cystine and other amino acids from the urine filtrate back into the bloodstream. The excess cystine remains in the urine, and in acidic conditions it forms crystals. These crystals can cluster into uroliths (stones) in the bladder or urinary tract. Stones irritate the bladder mucosa, causing inflammation, bleeding, and discomfort. In male dogs, stones can more easily lodge in the urethra due to its narrow diameter, creating a potentially fatal urinary blockage. In Newfoundlands, unlike most other breeds, the disease often appears by 5–6 months of age, and stones recur quickly even with treatment.
Complications - Cystinuria can result in: Recurrent bladder stones causing pain, frequent urination, blood in the urine, or urinary tract infections. Urethral blockages (especially in males) leading to complete inability to urinate — a medical emergency that can cause rapid kidney failure, coma, and death if untreated. Early age onset in Newfoundland type — stones may form in puppies before adulthood. Treatment resistance in Newfoundlands, with high recurrence rates despite intervention.
Why This Matters to Breeders and Vet - Breeders should be aware that cystinuria is preventable through genetic testing and breed management. Carriers should not be bred together. Informed breeding strategies can prevent producing affected puppies. Veterinarians play a key role in early diagnosis through urine testing (nitroprusside spot test), imaging, and owner education. Ongoing management after diagnosis — including diet modification, increased water intake, and possible medications — to prevent recurrence and manage stone formation. Awareness of the aggressive, early-onset form in this breed is crucial for timely intervention and avoidance of life-threatening urinary tract blockages.
Summary - Cystinuria (Newfoundland type) is a severe autosomal recessive kidney tubular transport disorder that prevents cystine reabsorption, causing early and repeated bladder stone formation in both sexes. It is more aggressive and less responsive to therapy in Newfoundlands compared to other breeds. The resulting stones can obstruct urine flow, leading to emergency situations and potential death. Diagnosis requires specialised urine testing and imaging, and while management is possible through diet, medication, and hydration, prevention through responsible breeding and genetic screening remains the most effective control strategy.
