urinary tract, 4) obstructive uropathy- urinary tract disease due to obstruction, and 5) urinary tract infections. Cause Cystinuria is caused by mutations in the SLC3A1 and SLC7A9 genes. These defects prevent proper reabsorption of basic, or positively charged, amino acids: cystine, lysine, ornithine, arginine. Under normal circumstances, 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, it forms cystine crystals, resulting in kidney stones. Cystine crystals form hexagonal-shaped crystals that can be viewed upon microscopic analysis of the urine. The other amino acids that are not reabsorbed do not create crystals in urine. The overall prevalence of cystinuria is approximately 1 in 7,000 neonates (from 1 in 2,500 neonates in Libyan Jews to 1 in 100,000 among Swedes). Pathophysiology Cystinuria is characterized by the inadequate reabsorption of cystine in the proximal convoluted tubules after the filtering of the amino acids by the kidney's glomeruli, 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 disease is attributed to deficiency in transport and metabolism of amino acids. Diagnosis Blood: Routine hemogram along with blood sugar, urea, and creatinine. Urine: For cystine crystals, and casts. The most specific test is the cyanide–nitroprusside test Ultrasound/CT scan to reveal if a stone is present. Genetic analysis to determine which mutation associated with the disease may be present. Currently genotyping is not available in the United States but might be available in Spain, Italy, UK, Germany and Russia (by private companies in Germany and Russia). Regular X-rays often fail to show the cystine stones, however they can be visualized in the diagnostic procedure that is called intravenous pyelogram (IVP). Stones may show up on XR with a fuzzy gray appearance. They are radioopaque due to sulfur content, though more difficult to visualize than calcium oxalate stones. Treatment Initial treatment is with adequate hydration, alkalization of the urine with citrate supplementation or acetazolamide, and dietary