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Cystinuria
Monday, 18 August 2003
Sunday, 28 November 2004

What

Cystinuria is an inherited metabolic disorder characterized by the abnormal transport of certain amino acids, cystine, lysine, arginine, and ornithine, in the intestines and kidneys. A large amount of undissolved cystine in the urine causes stones to form in the bladder, kidney, and ureter (the long tube that transports urine from the kidney to the bladder). Cystinuria has been separated in several groups based on which amino acids are involved. Type I consists of a defect in the transport of all the amino acids listed above in the kidneys and small intestine. In Type II, the transport of cystine and lysine is defective in the kidneys and only partially impaired in the intestines. In Type III, cystine and lysine transport in the kidney is impaired, but is normal in the intestines. Type IV, also called hypercystinuria, consists of a moderate increase of cystine in the urine, though intestinal absorption of amino acids is normal.

Who

The incidence of Cystinuria is about 1 in 7,000 people, equally prevalent in males and females. Males are more severely affected.

Signs and Symptoms

It is so difficult for cystine to dissolve in the urine that the formation of stones in the urinary tract is found in almost every patient with this disorder. Stones may first develop in infancy or childhood and are usually present before the age of 30 years. Stones can vary in size from very small to huge stones in the bladder. These stones can cause severe side pain that may become increasingly worse over time. This pain may travel to the pelvis, groin, and genital regions. Cystine stones are usually yellow in color and have a crystal appearance to the surface. Recurrent urinary tract infections frequently occur. Blood can also be found in the urine. Some patients have high blood pressure caused by damage to the kidneys. If severe, all of these problems can lead to kidney failure, however, some patients are asymptomatic even as adults.

Possible Causes

Cystinuria is an autosomal recessive disorder, meaning that the child inherits the defective gene from both parents. The gene that is defective is named rBAT and is found on chromosome number 2. This gene encodes for a protein that is responsible for transporting cystine and other amino acids across membranes. If this gene is defective, no protein is made and the amino acids cannot be transported out of certain systems (such as the kidney and intestine) and build up in those locations. A build up of cystine in the kidneys is especially harmful to the child. The insolubility of cysteine is what causes clinical symptoms. The excretion of the other amino acids does not cause any problems. The kidney is an organ in the body that is responsible for regulating the composition of the blood. Blood flows to the kidney through the renal artery and then back to the heart by the renal vein. Unwanted substances and wastes are filtered out of the blood and into the urine, which is carried by the ureter to the bladder. Most of the unwanted waste is dissolved in the urine but cystine is a different case. Cystine does not dissolve easily and this can result in the formation of crystals in the urine. These crystals start forming hard stones that can get stuck in the kidney, ureter or bladder. As these stones move through the kidney and ureter, they scrap along the passageways causing the severe side pain.

Diagnosis

Cystinuria is usually diagnosed after cystine stones are found in the kidney, ureter or bladder. Urine can also show high cystine levels and the crystals can be seen under a microscope.

Treatment

Treatment is aimed at relieving the symptoms and preventing the future development of stones. If a child has stones, the child should drink enough fluid (at least 6-8 glasses per day) in order to produce large amounts of urine. A diet low in sodium (sodium increases urinary amino acid excretion) and methionine (which is an amino acid that forms cystine) can lower cystine levels in the urine. Cystine can be dissolved in a low acid solution so some medications can be taken to lower the acid levels in the urine. If these stones are not excreted through the urine, they can be surgically removed. An alternative to surgery is lithotripsy. In this procedure, shock waves are used to break up the stones so that it can be easier to excrete them into the urine. Lithotripsy is not as successful removing cystine stones as it is with other kidney stones.

Prognosis

Children with Cystinuria will have this condition for the rest of their lives. The recurrence of cystine stones is common, and varies from child to child. This condition also does not end up affecting any other organs in the body.

Connect with other parents

In the spirit of community and support, Madisons Foundation offers the unique service of connecting parents of children with rare diseases. If you would like to be connected to other parents of children with this disease, please fill out this brief form.

Weblinks

Cystinuria support group:
A good website for families who want more information, including newsletters, a listserv, and a self-help handbook that can be dowloaded.

Cystinuria.org:
A good website for resources and information on Cystinuria, including a helpful link to a dictionary of medical terms, and a tutorial on how kidney stones are formed.

Cystinuria Bulletin Board
A great bulletin board for parents who want more information and support.

Family Village
A nice website with information about the disease as well as links to other informational sites and support groups.

Medline Plus
A comprehensive summary of the disease with nice definitions of technical terms.

Google Search for Cystinuria

References and Sources

Medline: www.nlm.nih.gov/medlineplus/ency/article/000346.htm Pediatric database: www.icondata.com/health/pedbase/files/CYSTINUR.HTM