Applied Clinical Genetics Case Library
Case 10

Signalment & History
Signalment:
  • 5-years-old
  • Neutered male
  • Aussie mix
History:
  • No significant history
Presenting Complaint
  • Pollakiuria, hematuria for two days. Excessive licking of the prepuce.
Physical Exam
  • Erythema around prepuce from excessive licking, slight sensitivity when palpating small bladder
  • Pollakiuria
  • Hematuria
  • Full-panel bloodwork – within normal limits
  • U/A – cystine crystals
  • Radiographs – small bladder, no uroliths visible
  • Ultrasound – many uroliths present
  • Using diagnostics in conjunction with Embark test results, cystinuria was diagnosed. 
  • Discussed with O starting the following maintenance:
    • Rx diet
      • Increasing dietary moisture significantly reduces urinary specific gravity and it is an effective way to enhance diuresis.
    • Blood work annually
    • U/A every 6 months
    • Abdominal ultrasound as indicated
Outcome
  • Knowing if a dog is at-risk for cystinuria enables a veterinarian to use ultrasound to check for uroliths (as many cystine stones are radiolucent), perform serial urinalyses, and recommend a prescription urinary diet before a dog requires surgery for this disease.
  • High-protein foods should be avoided in dogs at risk of cystine urolithiasis. Urine cystine excretion can be modulated by dietary protein intake, and more specifically methionine (a precursor of cysteine) and cysteine. Feeding a diet containing amounts of these essential amino acids close to their minimum is therefore recommended.
  • This gene has a dominant mode of inheritance. While dogs, male and female, homozygous or heterozygous for this variant are cystinuric, homozygous dogs have higher urinary cystine and COLA concentrations than the heterozygous dogs. Moreover, homozygous males typically show obstruction earlier in life (around one year of age) than heterozygous males (four to five years of age). The later age of onset of clinical signs (four to five years of age) in homozygous females may be explained by the anatomic differences between the sexes.
Additional Questions
  • Decrease. Both sexes are equally affected with excess cysteine in the urine, but obstruction of urine flow is more common in males due to differences in anatomy.

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