What causes cystinuria?

Cystinuria is caused by the defective transport of cystine and several other amino acids through the cells of the kidney and the intestinal tract.

What happens with cystine in the urine?

Although cystine is not the only overly excreted amino acid in cystinuria, it is the least soluble of all naturally occurring amino acids. Cystine precipitates, or crystallizes out of urine and forms stones (calculi) in the kidney, ureter, bladder, or anywhere in the urinary tract.

The cystine stones (below) compared in size to a quarter (a U.S. $0.25 coin) were obtained from the kidney of a young woman by percutaneous nephrolithotripsy (PNL), a procedure for crushing and removing the dense stubborn stones characteristic of cystinuria.

Cystine stones compared to quarter
Cystine stones compared to quarter

What problem do the cystine stones cause?

Small stones are passed in the urine. However, big stones remain in the kidney (nephrolithiasis) impairing the outflow of urine while medium size stones make their way from the kidney into the ureter and lodge there further blocking the flow of urine (urinary obstruction).

What happens with a urinary obstruction?

Obstruction of the urinary tract puts pressure back up on the ureter and kidney. It causes the ureter to widen (dilate) and the kidney to become compressed.

Obstruction of the urinary tract also causes the urine to be stagnant (not moving). Stagnant urine is an open invitation to repeated urinary tract infections.

Medically Reviewed by a Doctor on 8/31/2016

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