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Cystinuria

By

Christopher J. LaRosa

, MD, Perelman School of Medicine at The University of Pennsylvania

Last full review/revision Dec 2020| Content last modified Dec 2020
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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.

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 (amino acids are the building blocks for proteins). The excess cystine causes cystine kidney stones Stones in the Urinary Tract Stones (calculi) are hard masses that form in the urinary tract and may cause pain, bleeding, or an infection or block of the flow of urine. Tiny stones may cause no symptoms, but larger stones... read more Stones in the Urinary Tract 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 Overview of Kidney Failure Kidney failure is the inability of the kidneys to adequately filter metabolic waste products from the blood. Kidney failure has many possible causes. Some lead to a rapid decline in kidney function... read more develops.

There are two gene abnormalities that cause most cystinuria. The genes are recessive Recessive disorders Genes are segments of deoxyribonucleic acid (DNA) that contain the code for a specific protein that functions in one or more types of cells in the body. Chromosomes are made of a very long strand... read more , so people with the disorder must have inherited two abnormal genes, one from each parent ( ).

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.

Viewing the Urinary Tract

Organs of the Urinary Tract

Symptoms of Cystinuria

Diagnosis of Cystinuria

  • Analysis of kidney stones

  • Urine tests

A doctor tests for cystinuria when a person has recurring kidney stones. Stones that have been collected are analyzed.

Treatment of Cystinuria

  • Increasing fluid intake

  • Decreasing salt and protein in the diet

  • Drugs to make the urine more alkaline

  • Drugs to dissolve cystine

Treatment of cystinuria consists of preventing cystine stones from forming by keeping the concentration of cystine in the urine low. To keep the cystine concentration low, a person must drink enough fluids to produce at least 6 to 8½ pints (3 to 4 liters) of urine each day. During the night, however, when the person is not drinking, less urine is produced and stone formation is more likely. This risk is reduced by drinking fluids before going to bed.

Another treatment approach involves taking potassium citrate or potassium bicarbonate and sometimes acetazolamide to make the urine more alkaline (that is, less acidic) because cystine dissolves more easily in alkaline urine than in acidic urine. Efforts to increase intake of water and make the urine more alkaline can lead to abdominal bloating, making the treatment difficult for some people to tolerate. Consuming less salt and protein may help reduce the concentration of cystine in the urine.

If stones continue to form despite these measures, drugs such as penicillamine, tiopronin, or captopril may be tried. These drugs react with cystine to keep it dissolved. Penicillamine is effective in keeping the concentration of cystine in the urine low but it is toxic, so doctors give vitamin B6 Vitamin B6 Deficiency Vitamin B6 is in most foods, but people can have vitamin B6 deficiency if they do not absorb it properly. Many foods contain vitamin B6, but extensive processing can remove the vitamin. People... read more (pyridoxine) supplements to people taking penicillamine. Tiopronin can be used instead of penicillamine to treat some children because it has a lower frequency of side effects. Captopril is slightly less effective than penicillamine but is less toxic. Although the treatments are usually effective, there is a fairly high risk that stones will continue to form.

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