Feline cystinuria due to a defect in tubular reabsorption of cystine, with crystalluria and calculi that can obstruct the urinary tract. It is associated with variants of the SLC7A9 gene and has been described in Maine Coon, Sphynx and domestic longhair cats, among others. Autosomal recessive inheritance. The molecular test is complementary to — not a substitute for — urinalysis and stone analysis.

Documented breeds: Maine Coon, Maine Coon Polydactyl, Siamese, Siberian, Sphynx and domestic longhair (OMIA:002023). Carrier frequencies: limited data.

- Recurrent cystitis, haematuria and stranguria
- Hexagonal cystine crystals in sediment or cystine calculi
- Urinary obstruction, more severe in males due to their anatomy
- Possible renal failure in unresolved obstructions

Mizukami et al. (2016) identified three missense variants of SLC7A9 in affected cats: p.Asp236Asn (exon 5), p.Val294Glu (exon 7, in Maine Coon and Sphynx) and p.Thr392Met (exon 10). The variants segregated with the disease in the cases studied. OMIA:002023.

- Do not cross two carriers: 25 % affected homozygotes
- Carrier × clear is acceptable; test the offspring intended for breeding
- In homozygotes: abundant hydration, alkaline urine and crystalluria control; monitor obstruction in males
- After a confirmed clinical case, do not repeat the parental mating and communicate the status to the buyer

Differential diagnosis with oxalate or urate uroliths and with cystinuria from other causes. Diagnosis by hexagonal crystals in sediment or stone analysis. No curative treatment: dietary management and management of crystalluria.

1. Mizukami K et al. 2016, cistinuria asociada a distintas variantes de SLC7A9 en el gato (PMID 27404572)
2. OMIA:002023 Cistinuria felina (tipo B)