Breeds Affected: Labrador Retriever
Samples Accepted: Blood, Buccal Swabs
Disease Information: The kidneys of dogs with Cystinuria Type I-A are unable to reabsorb certain amino acids. Excess cystine is excreted in the urine, resulting in urolithiasis, the formation of calculi (crystals, stones) in the urinary tract. This leads to obstruction of the urinary tract and recurrent cystitis. Due to features of anatomy, male dogs are more likely to have symptoms than females.
Inheritance Information: Cystinuria Type I-A is autosomal recessive, meaning that animals with two copies of this allele will be affected. Animals with one copy of the gene will be clinically-normal carriers.
The possible genotypes are:
N/N The dog is normal, and cannot produce affected offspring.
N/cys1a The dog is a carrier, and can pass the allele on to approximately 50% of any offspring. If bred to another N/cys1a carrier, approximately 25% of the offspring will be normal, 50% will be carriers, and 25% will be affected.
cys1a/cys1a The dog is affected. If bred to a normal animal, 100% of the offspring will be carriers. If bred to an N/cys1a carrier, 50% of the offspring will be carriers and 50% will be affected.
– Carriers may be bred to normal animals (N/cys1a x N/N) without any risk of producing affected offspring. The offspring should be tested before breeding to determine if they are carriers or normal.
– Breeding two carriers (N/cys1a x N/cys1a) is not recommended due to the possibility of 25% of the offspring being affected.
– Affected animals (cys1a/cys1a) should not be used for breeding.
Test Information: This mutation test identifies a single base deletion in exon 1 of the SLC3A1 gene.
Brons, A.K., Henthorn, P.S., Raj, K., Fitzgerald, C.A., Liu, J., Sewell, A.C., Giger, U.: SLC3A1 and SLC7A9 mutations in autosomal recessive or dominant canine cystinuria: a new classification system. J Vet Intern Med 27:1400-8, 2013. Pubmed reference: 24001348. DOI: 10.1111/jvim.12176.
Further information is available at the Online Mendelian Inheritance in Animals website.