Cystinuria

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Cystinuria
Classification and external resources
Chemical structure of cystine formed from L-cysteine (under biological conditions)
ICD-10	E72.0
ICD-9	270.0
OMIM	220100
DiseasesDB	3339
MedlinePlus	000346
eMedicine	med/498
MeSH	D003555

Cystinuria is an inherited autosomal recessive^[1] metabolic disorder that is characterized by the formation of cystine stones in the kidneys, ureter, and bladder.

Signs and symptoms

In acidic pH, cystine crystals are formed in the urine. These crystals may be converted in to renal calculi

Causes

Cystinuria is characterized by the inadequate reabsorption of cysteine in the proximal convoluted tubules during the filtering process in the kidneys, thus resulting in an excessive concentration of this amino acid in the urine. Cystine may precipitate out of the urine, if the urine is neutral or acidic, and form crystals or stones in the kidneys, ureters, or bladder. It is one of several inborn errors of metabolism included in the garrod's tetrad. The disorder is attributed to deficiency in transport and metabolism of amino acids.

Pathophysiology

Cystinuria has an autosomal recessive pattern of inheritance.

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. These defects prevent proper reabsorption of basic, or positively charged amino acids such as histidine, lysine, ornithine, arginine and cysteine.^[2]

Normally this protein allows certain amino acids, including cysteine, 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 cysteine in the urine increase, the crystals typical of cystinuria are able to form, resulting in kidney stones. Cystine crystals form hexagonal-shaped crystals which can be viewed upon microscopic analysis of the urine. The other amino acids that are not reabsorbed do not create crystals in urine. The disorder affects 1 in 10,000 people, making it the most common genetic error of amino acid transport. Cystinuria is inherited in an autosomal recessive pattern.

Treatment

Alkalinization of urine can help reduce stone formation.^[3]

Occurrence in animals

This disease is known to occur in only two mammalian species. These include humans, and canines like the Maned Wolf of South America. Newfoundland dogs are at an increased risk for cystinuria, compared with other breeds of dog.^{[citation needed]}

References

See also

• Cystine
• Cysteine
• Thiola
• International Cystinuria Foundation
• Hartnup disease
• Cystinosis
• Homocystinuria

External links

• International Cystinuria Foundation homepage
• Cystinuria discussion forums
• Cystinuria Clearinghouse