cystinuria

The cystinuria - An inherited disorder (see metabolism, inborn errors of) in which the kidneys are unable effectively to process certain amino acids (the chemical compounds that make up proteins). Cystinuria is inherited in an autosomal recessive manner (see genetic disorders) and occurs in around one in 1,000 births.

Under normal circumstances, blood is filtered as it passes through the kidneys; a wide range of substances is removed, then useful compounds, such as amino acids, are reabsorbed. In cystinuria, this process does not work effectively. As a result, high levels of four amino acids, particularly cystine, occur in the urine. This excess cystine can result in the development of a rare form of kidney stones (see renal calculi) in both adults and children.

Cystinuria is usually detected in people who have symptoms of kidney stones, or in those who have passed stones that, on analysis, are found to contain cystine. The diagnosis can be confirmed by urine tests that measure the levels of amino acids. Treatment involves drinking large amounts of fluids regularly in order to dilute the urine and reduce the concentration of cystine. If the levels of cysteine remain high, the drug penicillamine may be required to help prevent the formation of new stones.