Cystinuria

What is cystinuria?

Cystinuria is a genetic condition characterized by the buildup of cystine crystals or stones in the kidneys and bladder. Cystine is an amino acid, one of the building blocks of proteins. Normally, cystine is reabsorbed back into the bloodstream after blood entering the kidneys is filtered to create urine. Only small amounts of cystine can stay dissolved in urine, usually 300 mg/L. People with cystinuria cannot properly reabsorb cystine back into their bloodstream. As urine becomes more concentrated in the kidneys, the cystine cannot stay dissolved and forms crystals. As these crystals become larger, they form stones that may lodge in the kidneys or in the bladder. Sometimes cystine crystals combine with calcium in the kidneys to form large stones. Blockages in the urinary tract by these crystals and stones can cause intense pain, called renal colic, and reduce the ability of the kidneys to eliminate wastes through urine. The stones also provide sites where bacteria may cause infections.

Cystinuria cannot be cured, but treatment can reduce the incidence of stones. Initial therapy involves increased fluid intake sufficient to create at least 3 liters of urine per day. The goal is to reduce the urinary cystine concentration to less than 300 mg/L. Methionine is a dietary precursor of cystine so a low methionine diet is helpful. (High methionine foods include meat, fish, sausage, poultry, eggs, cheese and soy.) A high fiber, low salt diet is also recommended.

Alkalinization is the next step in treatment. Cystine is more soluble at a higher (more alkaline) pH. In general, the optimal range for an active cystine stone former is 7.0-7.5. This is usually achieved with potassium citrate supplements, either tablets or liquid. (The pH can be monitored with special urinary dipsticks called "StoneGuard II" and are commercially available at www.uridynamics.com.) The dosage of potassium citrate should be adjusted to maintain the suggested pH. (Potassium citrate with increase the pH.)

Other medications can be used in resistant cases such as captopril, thiola and penicilamine. These last two medications have significant side effects and need careful monitoring. Bucillamine is another medication that appears promising in reducing urinary cystine levels. At this time, it is only available in Japan and South Korea.

How common is cystinuria?

Cystinuria affects approximately 1 in 10,000 people.

What genes are related to cystinuria?

Mutations in the SLC3A1 and SLC7A9 genes cause cystinuria.

The SLC3A1 and SLC7A9 genes provide instructions for producing the two parts of a transporter protein that is made primarily in the kidneys. Normally this protein allows certain amino acids, including cystine, to be reabsorbed into the blood from the filtered fluid that will become urine. Mutations in either of these genes disrupt the ability of this transporter protein to reabsorb these amino acids, allowing them to become concentrated in the urine. As the levels of cystine in the urine increase, the crystals typical of cystinuria are able to form. The other amino acids that are not reabsorbed do not create crystals in urine.

Read more about the SLC3A1 and SLC7A9 genes.

How do people inherit cystinuria?

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

Where can I find information about treatment for cystinuria?

These resources address the management of cystinuria and may include treatment providers.

• MedlinePlus Encyclopedia: Cystinuria
• MedlinePlus Encyclopedia: Cystinuria Image

You might also find information on treatment of cystinuria in Educational resources and Patient support.

Where can I find additional information about cystinuria?

You may find the following resources about cystinuria helpful. These materials are written for the general public.

• MedlinePlus - Health information (3 links)
• Additional NIH Resources - National Institutes of Health (2 links)
• Educational resources - Information pages (4 links)
• Patient support - For patients and families (2 links)

You may also be interested in these resources, which are designed for healthcare professionals and researchers.

• Gene Tests - DNA tests ordered by healthcare professionals
• ClinicalTrials.gov - Linking patients to medical research
• PubMed - Recent literature
• Online Books - Medical and science textsScriver's Online Metabolic and Molecular Bases of Inherited Disease (OMMBID):Cystinuria
• OMIM - Genetic disorder catalog

What other names do people use for cystinuria?

• CSNU

See How are genetic conditions and genes named? in the Handbook.

What if I still have specific questions about cystinuria?

• See How can I find a genetics professional in my area? in the Handbook.
• Ask the Genetic and Rare Diseases Information Center.
• Submit your question to Ask the Geneticist.

Where can I find general information about genetic conditions?

The Handbook provides basic information about genetics in clear language.

• What does it mean if a disorder seems to run in my family?
• What are the different ways in which a genetic condition can be inherited?
• If a genetic disorder runs in my family, what are the chances that my children will have the condition?
• Why are some genetic conditions more common in particular ethnic groups?

These links provide additional genetics resources that may be useful.

• Genetics and health
• Resources for Patients and Families
• Resources for Health Professionals

What glossary definitions help with understanding cystinuria?

acids ; amino acid ; autosomal ; autosomal recessive ; bacteria ; calcium ; cell ; cystine ; gene ; infection ; kidney ; kidney stones ; mutation ; protein ; recessive ; sign ; stone ; symptom

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.