Cystinuria is a genetic disorder that causes the formation of stones in the kidneys, urethra, bladder and the intestines. Amino acids, especially cysteine, are the main components of these stones.
Causes and Symptoms of Cystinuria
Cystinuria is a genetic condition that is inherited as an autosomal recessive disease; this means that the defective gene is received from both parents. The main causes of cystinuria include:
- Mutations in SLC3A1 and SLC7A9 genes
- A malfunction in the transportation and metabolism of amino acids
- Defective genes prevent the reabsorption of positively charged amino acids like cysteine, leading to a higher concentration in the urine. This leads to the formation of stones.
Cystinuria is classified into three types:
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Type I Cystinuria:
This type of cystinuria is characterized by a malfunction in the kidneys and the small intestine.
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Type II Cystinuria:
In Type II Cystinuria, the impairment is more in the kidneys when compared to the small intestine.
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Type III Cystinuria:
In this variant, the transportation of amino acids is weakened in the kidneys but remains normal in the small intestine.
Cystinuria presents the following symptoms:
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Renal colic:
A spasm moving from the front to the back in the abdominal and groin areas is common in people with kidney stones caused by cystinuria. Since this condition causes a quicker formation of stones, the pain linked to renal colic may also present itself early.
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Chronic pain:
Chronic back and abdominal pain and a continuous dull throb in the area where the kidneys are located are common symptoms that can wear a person down considerably.
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Hematuria:
This describes the presence of Red Blood Cells (RBCs) in the urine and is a result of the scarring and damage caused by the sharp edges of the crystal-like stones.
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Hydronephrosis:
In this condition, the stones block the proper passage of urine and cause fluid retention in the kidneys. This can lead to the enlargement of kidneys and various life-threatening complications.
Diagnosis, Treatment and Prevention of Cystinuria
Since the stones associated with cystinuria do not show up on conventional imaging studies like X-rays and Magnetic Resonance Imaging (MRI) scans, the diagnosis of cystinuria is difficult. An imaging technology called Intravenous Pyelogram may be more useful in capturing the cysteine stones.
A 24-hour urine sample and a cyanide-nitroprusside test may also be useful in determining the presence of cysteine crystals.
The major goal of Cystinuria treatment is to relieve pain and prevent a recurrence, and since people with this condition suffer from chronic pain, it can lead to severe debilitation and even depression in some cases.
Common treatment strategies used are:
- Pain relievers
- Increased fluid intake
- Reduction of salt and protein intake
- Administration of medicines that can dissolve cysteine
- Chelation therapy
- Extracorporeal Shock Wave Lithotripsy (ESWL) to try and break up the stones
- Surgery, kept as the last option, is performed to remove the cystine stones
Commonly recommended preventive measures:
- Increasing water intake to produce lots of urine; this helps flush out excessive cysteine and stones
- People who have been treated should follow up regularly to check for recurrences
While people with cystinuria might not be completely cured, a proper pain management regimen and appropriate treatment can restore normalcy to their lives.
References
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Sahota, A., Parihar, J. S., Capaccione, K. M., Yang, M., Noll, K., Gordon, D., . . . Tischfield, J. A. (2014, November). Novel cystine ester mimics for the treatment of cystinuria-induced urolithiasis in a knockout mouse model. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/25443947
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Cystine stones: A single tertiary center experience – Abstract. (2014, November 20). Retrieved from https://www.urotoday.com/recent-abstracts/endourology-urolithiasis/stone-disease/76484-cystine-stones-a-single-tertiary-center-experience-abstract.html
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Shim, M., & Park, H. K. (2014, August). Multimodal treatments of cystine stones: An observational, retrospective single-center analysis of 14 cases. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/25132945
Thomas, K., Wong, K., Withington, J., Bultitude, M., & Doherty, A. (2014, May). Cystinuria-a urologist’s perspective. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/24662732
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Kummer, S., Venghaus, A., Schlune, A., Leube, B., Eggermann, T., & Spiekerkoetter, U. (2014, January). Synergistic mutations in SLC3A1 and SLC7A9 leading to heterogeneous cystinuria phenotypes: Pitfalls in the diagnostic workup. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/24045899
Izol, V., Aridogan, I. A., Karsli, O., Deger, M., & Satar, N. (2013, December). The effect of prophylactic treatment with Shohl’s solution in children with cystinuria. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/23806278
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