
Testing of cats: Cystinuria, type I-A
Cystinuria, type I-A in Domestic Shorthair
Cystinuria is an inherited metabolic disorder of amino acid transport in the kidneys. In affected individuals, cystine is accumulated in the urine, cystine crystals and urinary stones are formed. These irritate the urinary tract, causing urinary stagnation and increasing the susceptibility of the urinary tract to infection. Clinically, cystinuria is manifested by dark and distinctly foul-smelling urine with an admixture of blood. Urination is painful and often unsuccessful. Secondary clinical signs such as lethargy, excessive salivation, impaired intestinal absorption and changes in renal function leading to hyperammonemia can be fatal.
As in humans and dogs, the disease is genetically heterogeneous in cats. A missense mutation c.1342C>T in the SLC3A1 gene has been identified in the domestic shorthair cat.
The mode of inheritance of the mutation is autosomal recessive. This means that only individuals who inherit the mutated gene from both parents will develop the disease. Carriers of the mutated gene are clinically healthy but pass the mutation on to their offspring. In the case of a mating between two heterozygous individuals, theoretically 25% of the offspring will be completely healthy, 50% of the offspring will be carriers and 25% of the offspring will inherit the mutated gene from both parents and will therefore be affected by the disease.
The genetic test can clearly reveal the genotype of the animal and is a useful tool for breeders to prevent unintentional breeding of affected kittens.
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References:
Mizukami, K., Raj, K., Giger, U. : Feline cystinuria caused by a missense mutation in the SLC3A1 gene. J Vet Intern Med 29:120-5, 2015. Pubmed reference: 25417848.