Answer: Individuals with a high concentration of cysteine in their urine, show symptoms of cystinuria.
Explanation:
Cystinuria is an hereditary and rare disease in which stones of an amino acid called cystine form mostly in the kidney but also in the ureter and bladder. This is a dimeric amino acid which is formed by two cysteine molecules linked by a disulfide bond. L-cysteine is a non-essential sulfuric amino acid found in a wide variety of foods, some of which are proteins. This condition is passed from parents to children so it is hereditary, the person must inherit the defective gene from both parents.
Cystinuria is caused when there is a high concentration of cystine in the urine. Normally, most cystine dissolves, enters the kidneys and returns to the bloodstream. However, people with cystinuria have the genetic defect that interferes with this process. This condition is due to a defective transport of cystine in the apical membrane of the intestinal epithelium and proximal renal tubule. The result is an absence of cystine reabsorption in the renal proximal tubule producing an excess of cystine in urine and with the consequent formation of kidney stones. Cystine stones are very difficult to remove by lithotripsy unlike the rest of the stones. Therefore, a non-invasive therapy should be carried out to prevent the recurrence of stone formation. This therapy would be based on a high intake of liquids, alkalization of urine, and use of chelating agents. In order to preserve kidney function, a combination of these three therapeutic measures is necessary to reduce both the recurrence and the morbidity of the disease.
