Hyperuricosuria is a defect of renal uric acid transport caused by a variant of the SLC2A9 gene, historically described as G616T (p.Cys188Phe) and also noted as Cys181Phe depending on the reference transcript. It increases urinary urate excretion and the risk of urate uroliths. The Dalmatian is the paradigmatic breed.

The Dalmatian is the paradigmatic breed: all individuals are homozygous. In other breeds the allele circulates at low frequencies (0.001-0.15): American Staffordshire Terrier, Australian Shepherd, German Shepherd, Giant Schnauzer, Jack/Parson Russell Terrier, Labrador retriever, Large Münsterländer, Pomeranian, South African Boerboel and Weimaraner. Bulldog 0.16 and Black Russian Terrier 0.51 (Karmi et al. 2010). Testing is advisable in breeds with uric urolithiasis.

- Persistent hyperuricosuria and hyperuricemia (no clinical signs until stones appear)\n- Ammonium urate urolithiasis (radiolucent stones, in the bladder and sometimes the urethra or kidney)\n- Dysuria, hematuria, pollakiuria and, in males, urethral obstruction by stones\n- Recurrent urinary infections favoured by the uric substrate\n- In cases of obstruction: signs of post-renal azotemia, vomiting, depression\n- In the Dalmatian: in some cases, urate deposition in skin and other tissues (rare)

The genetic basis of Dalmatian hyperuricosuria was historically attributed to a defect in tubular urate transport. Bannasch et al. (2008) identified the missense variant of SLC2A9 (G616T; p.Cys188Phe) responsible for the trait, also present in Bulldog and Black Russian Terrier. Karmi et al. (2010) estimated the allele frequency in different breeds.

- The variant is autosomal recessive: only homozygotes have the complete defect; heterozygotes are carriers.\n- Do not cross two carriers with each other (25% risk of homozygotes).\n- In the Dalmatian the allele is fixed, so it cannot be eliminated by selection; management focuses on diet and prevention of uroliths.\n- In other breeds with the allele present, use the test to reduce the allele frequency.\n- In homozygotes, recommend a low-purine diet, abundant hydration and urinary monitoring.

Differential diagnosis with other causes of uric urolithiasis: urea-splitting bacterial infection (Proteus, Staphylococcus) that alkalinizes urine and precipitates struvite-ammonium-urate, portosystemic hepatic insufficiency (uric acid is not converted in the liver and is excreted by the kidney) and, in the Bulldog, uric urolithiasis associated with urachal fistula. The SLC2A9 genetic test explains the predisposition but does not replace stone analysis (infrared spectrophotometry) or urine culture when there is infection. Dietary management (low-purine diets, moderate alkalinization with potassium citrate, hydration) reduces recurrence; obstructive stones require intervention (retrograde manipulation, cystotomy, lithotripsy).

1. Bannasch D et al. 2008, mutaciones en SLC2A9 causan hiperuricosuria e hiperuricemia en el perro (PMID 18989453)
2. Karmi N et al. 2010, validación de un test de orina y caracterización de la mutación en Bulldog y Black Russian Terrier (PMID 20673090)
3. Karmi N et al. 2010, frecuencia estimada de la mutación de hiperuricosuria en distintas razas (PMID 21054540)
4. OMIA:000584 Hiperuricosuria (SLC2A9)