Cystine stones are formed by the combination and growth of cystine with lysine, arginine or ornithine. Cystine stones account for 1 to 3 percent of all stones. Cystinuria is a genetic disorder caused by urinary cystine supersaturation due to the inability of the renal tubules to reabsorb certain specific amino acids. Males and females have an equal chance of developing cystine stones. Since there is no cure for the genetic defect, all treatment is basically symptomatic and therefore requires more attention to the diet. Dietary methionine is metabolized in the body and converted to cystine, so patients with cystine stones should adopt a low-methionine diet, such as eggs, poultry, fish and meat. Fruits and vegetables can turn urine to alkaline, which is better for preventing cystine stones, and drinking more water to reduce the concentration of cystine to achieve the therapeutic effect. Researchers have measured that if each person consumes 20 grams of protein per day, urinary cystine can be reduced to 1/3 of normal, except that the disease is symptomatic in children, and restricting protein intake to children can cause malnutrition and affect physical development. Since most patients do not accept a restricted diet, drinking large amounts of water evenly is a proven way to treat and prevent cystine stones.