Cystinuria is a rare hereditary kidney disorder that results in excretion of the amino acid cystine into the urine, often causing cystine stones to form in the urinary tract.
(See also Introduction to Congenital Kidney Tubular Disorders and Kidney Stones.)
Cystinuria is caused by an inherited defect of the kidney tubules. The defect causes people to excrete excessive amounts of the amino acid cystine into the urine. The excess cystine causes cystine kidney stones to form in the kidneys, bladder, renal pelvis (the area where urine collects and flows out of the kidney), or ureters (the long, narrow tubes that carry urine from the kidneys to the bladder). Occasionally, kidney failure develops.
There are two gene abnormalities that cause most cystinuria. The genes are recessive, so people with the disorder must have inherited two abnormal genes, one from each parent (see Figure: Non–X-Linked (Autosomal) Recessive Disorders).
Sometimes, a person who has only one abnormal gene (a carrier), such as a parent of a person who has cystinuria, may excrete larger than normal amounts of cystine into the urine but seldom enough to form cystine stones.
Boys are generally affected more than girls.

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