Cystine kidney stones, one of the hardest formations of kidney stones, occur most often in children and young adults with a rare, hereditary disorder known as cystinuria. While no cure exists, people with cystinuria usually develop cystine stones throughout their lifetimes unless they take preventative medications or receive kidney transplants. Less than 1% of kidney stones in adults and 6% to 8% in children are made of cystine (a crystalline, sulfur-containing amino acid).
A kidney stone is a stone-like mass that forms when minerals and other substances in the urine accumulate to form crystals on the inner surfaces of the kidneys, and sometimes on portions of the urinary tract. In most people, chemicals are present in the urine that prevents or inhibits these crystals from accumulating into a hard mass. In susceptible people, however, these chemicals seem to malfunction, and as a result, fail to inhibit the formation of kidney stones. Most stones are tiny enough to pass out of the body through the urinary tract without pain or discomfort. Yet, some kidney stones get so large they become lodged in the urinary tract and can only be removed through surgery.