Cystinuria is a hereditary disease that is responsible for development of recurrent kidney stones. It is an autosomal recessive genetic disorder caused by mutation in SLC3A1 and SLC7A9 genes. In cystinuria there is too much excretion of cystine in urine. Cystine is a type of amino acid. Amino acids are formed from protein that we eat. They have wide variety of functions in our body. In fact they are considered body’s building blocks.
Due to the defect in the gene, cystine rather getting absorbed back into the bloodstream gets excreted in excess.However, cystine is least soluble in urine hence it forms into crystals in the kidney. Its increased concentration ultimately leads to formation of recurrent kidney stones. Kidney stones formed due to cystinuria produce symptoms such as pain in abdomen, blood in urine, frequent urinary tract infection, etc. Since it is a genetic disease treatment is aimed to alleviate symptoms and prevent recurrence of stone formation.
What Is The Cause Of Cystinuria?
Cystinuria is passage of cystine in urine. It is a hereditary disorder caused by mutation in genes that are inherited from both the parents.The defect occurs in SLC3A1 and SLC7A9 genes. The main function of these genes is to instruct the body to manufacture certain transporter protein in the kidneys. The transporter protein is involved in reabsorption of amino acids when the blood passes through the kidneys.
However, because of the defect in gene, the transporter protein is not able to reabsorb the amino acid cystine. Since cystine is slightly soluble in urine if it is not reabsorbed, it will start building up to abnormal high level in the kidney. It then forms crystals and cystine stones.The hard stones get stuck inside the kidney and organs of urinary tract. Both males and females are equally affected with cystinuria.
Signs And Symptoms Of Cystinuria
Cystinuria in itself does not produce any symptoms thus patient is not aware that he is having cystinuria. However, eventually when cystine stones develop in kidney the disorder starts producing symptoms. Cystinuria is a lifelong condition. Symptoms usually develop in young adults. It occurs in people between 20 to 30 years. In rare cases it may develop in elderly and infants.
Following are symptoms produced by stones formed due to cystinuria in the urinary tract:
- Blood in urine.
- Pain in abdomen and in flanks. The pain is almost always on one side of the flank.
- Vomiting and nausea.
- Burning in urine due to infection in urinary tract.
- Passage of stone in urine.
- Increased frequency of passing urine.
Patient may suffer from complications such as recurrent urinary tract infection, hydronephrosis (swelling of kidney caused due to obstruction of urine flow from stone located in ureter), in rare cases kidney damage.
Diagnosis And Treatment Of Cystinuria
For diagnosis of cystinuria the doctor inquires about anyone in the family suffering from kidney stone disease. Besides proper medical and family history he may also suggest certain tests that will complement in confirming the diagnosis. These tests include urine examination, X-ray of kidney, ureter and bladder, intravenous pyelogram, sonogram of urinary tract, and CT scan.
The initial treatment is aimed to modify patient’s lifestyle. This will prevent formation of calculi. One of the simplest natural ways is to increase intake of water so that the crystals are flushed out through urine. Patient must reduce consumption of salt in his diet.
Cystine is more soluble when the urine is more alkaline. This means its pH must be higher. Patient is thus advised to take alkalizing agents that help to dissolve cystine in urine. Thus it will get excreted from the body rather than building up in kidney to form stones. Alkalizing medicines are available over the counter.
Chelation therapy with certain medication also helps to cystine crystals. The drugs in chelation therapy combine together with cystine and form a complex compound that can dissolve in urine.
Patient may need pain medicines to control severe kidney stone pain.
If stones are very large and if they block the urine flow, the stone may have to be removed surgically. There are several procedures followed to remove the stone. Electrocorporeal shock wave lithotripsy (ESWL) and percutaneous nephrolithotomy are two common procedures that may be needed to remove a large stone.
Usually patients suffering from cystinuria have to take lifelong treatment. Surgery may remove the stone but it cannot stop its recurrence. To avoid recurrence of stone formation, patient has to drink large amount of water daily, limit intake of salt for lifetime and take medications that help to prevent kidney stone formation.