Clinical Comments:

Cystinuria is disorder that affects a dog's ability to filter cystine out of urine. Cystine is generally insoluble in the acidic conditions of canine urine, allowing it to crystallize and form caliculi, also known as stones. Not every dog that has the mutation responsible for Cystinuria will exhibit symptoms. Stones causing inflammation and blockage are often more common in males, due to their long, narrow urethra. Females exhibit symptoms much less frequently and may never show signs of disease. In many breeds, symptoms are first noted at around 4-5 years. However, Newfoundlands carry a more severe form that other breeds, with problems developing and noticed at 6-12 months. Newfoundlands are much more likely to experience recurring urethral blockages, and require surgical intervention. Please note that the tests, and type of inheritance, and mutations for Cystinuria vary by breed. It is important to choose a test appropriate for your breed/type.

Presenting signs include recurrent cystitis, hematuria, and stranguria. Calculi may become lodged in the urinary bladder, urethra, or kidney, causing partial or complete urinary blockage. A relatively earlier age of onset has been identified in Newfoundlands compared to other breeds that develop cystinuria. Diagnosis is achieved by identifying characteristically hexagonal cystine crystals in urine sediment, or cystine calculi in stone analysis. Metabolic screening tests on urine (cyanide nitroprusside test, amino acid chromatography or amino acid quantification) can detect cystinuria before or after clinical onset. Since cystine easily precipitates in acidic urine to form uroliths, treatment includes alkalinization of the urine, high fluid intake, and drugs that increase cystine solubility (Harnevik et al., 2006)

Breed-Specific variants: Newfoundland - g.46706001C>T; c.586C>T; p.(R196*). Labrador Ret. c.350delG; p.(G117Afs*41)