Kidney stones are the result of the concentration of some substances in the urine getting high enough that small, hard masses are formed. Kidney stones are made of cysteine. A rare case of kidney stones can lead to extreme pain and discomfort, as well as kidney and bladder damage.
Cysteine
Cysteine is an amino acid. Amino acids are small, organic compounds that can be combined to make proteins, Medline says. There are 20 amino acids; some of them, called essential amino acids, cannot be made by the human body and must be ingested. Non-essential amino acids, which include cysteine, can be synthesized by the body.
Cystinuria and Kidney Stones
Cysteine molecules travel throughout the blood and can sometimes make their way into kidneys. Normally, the kidneys reabsorb the cysteine molecules, which keeps cysteine from appearing in the urine. However, patients with cystinuria have a genetic disorder that causes cysteine to accumulate in the urine. When present at high concentrations, the cysteine molecules aggregate to form kidney stones.
Genetics
Cystinuria is an autosomal recessive disease, which means that patients must inherit a mutated copy of the gene from both parents, according to the Genetics Home Reference. Two different genes, known as SLC3A1 and SLC7A9, can be mutated and cause cystinuria. These genes encode the parts of a protein that's necessary to transport cysteine out of the urine in the kidneys. The Genetics Home Reference says one in every 10,000 people has cystinuria.
Symptoms and Diagnosis
Patients with cystinuria are prone to develop kidney stones that are made of cysteine. Medline says common symptoms of these sorts of kidney stones include blood in the urine and sharp pain felt in the flank that may worsen over a few days. Analysis of the urine shows high levels of cysteine, which is usually enough for a definitive diagnosis.
Treatment
Cysteine-based kidney stones, according to UrologyHealth.org., are often treated by giving the patient lots of fluids in an attempt to dissolve the stone. If the kidney stone is small enough, it may make its way through the urinary system on its own. Larger stones can become lodged in the kidneys and require other treatments. Sometimes kidney stones can be broken up using ultrasound, though UrologyHealth.org says stones made of cysteine are resistant to this type of treatment. Ureteroscopy can be used to remove stones that are trapped in the ureter. Large stones can be surgically removed.
