Cystinuria (CU) affects kidney function with affected dogs being unable to reabsorb cystine from the urine. This excess cystine can cause crystals or stones to block the urinary tract and lack of treatment can cause kidney failure and death.
This is an autosomal recessive condition in most breeds, but autosomal dominant in the Australian Cattle Dog, and is caused by a mutation in the SLC3A1 gene.