Cystinuria is a rare genetic disorder categorised by the abnormal build-up of the amino acid cystine as well as three chemically similar amino acids: arginine, lysine and ornithine in the urine, leading to stone formation in the kidney, bladder and urinary tract . This condition is hereditary, and individuals with cystinuria inherit specific genetic mutations from both parents.
cystinuria

This defect in the gene causes cystine to get deposited in the kidneys, which are the vital organs that control what goes in and out of the bloodstream. The kidneys carry out several important functions, including:

  • Reabsorbing essential minerals and protein back into the system
  • Filtering the blood to clear out toxic waste products
  • Producing urine to eliminate waste from the body

In a person with this condition, the amino acid cystine accumulates and forms stones instead of travelling back into the bloodstream.

Read this article to get an insight into the causes, symptoms, diagnosis, and treatment options available for this genetic disorder.

To Maintain Your Kidney Health, Buy From Our Best-Selling Blood Pressure Monitors

Causes

Cystinuria is primarily caused by mutations in the SLC3A1 and SLC7A9 genes responsible for encoding proteins that help transport cystine from the kidneys into the urine. When these genes are mutated, the normal transport mechanism is disrupted, leading to the accumulation of cystine in the urine and the formation of kidney stones. Cystinuria disorder usually follows an autosomal recessive pattern, meaning that both parents carry the mutated gene for their child to develop the disorder.

Also Read: Kidney Failure: Causes, Symptoms And Treatment

Symptoms

The most common and noticeable symptom of cystinuria is the recurrent formation of kidney stones. These stones usually vary in size and may cause excruciating pain as they pass through the urinary tract. Other symptoms associated with cystinuria include:

Haematuria: Blood in the urine may occur due to irritation caused by the passage of kidney stones.

Frequent Urinary Tract Infections: The obstruction of urine flow by kidney stones can create an environment conducive to bacterial growth, leading to recurrent urinary tract infections.

Abdominal/ Back Pain: Kidney stones can cause pain in the abdomen or lower back region, specifically during the passage of stones through the urinary tract.

Also Read: Kidney Health: Know About 11 Early Warning Signs of Renal Disease

Diagnosis

Cystinuria is typically diagnosed through medical history, physical examination, and laboratory tests. A healthcare provider may inquire about the patient's family history and symptoms and conduct a physical examination. Genetic testing may also be carried out to identify specific mutations in the SLC3A1 and SLC7A9 genes.

Laboratory tests, such as a 24-hour urine collection, can help quantify the amount of cystine in the urine.

24-hour urine collection: The patient will be asked to collect urine in a big container for over 24 hours, and the urine will be sent to a laboratory for further analysis.

Intravenous pyelogram: It is an X-ray examination of the kidneys, bladder, and ureters. This method makes use of a dye in the bloodstream to help determine the cystine stones.

Abdominal CT scan: CT scan uses high-defined X-rays to produce images of the structures within the abdomen to determine for stones inside the kidneys.

Urinalysis: It is an examination of urine in a laboratory that may involve looking at the colour and physical appearance of the urine, examining the urine under a microscope, and chemical analysis to detect specific substances, such as cysteine.

Treatment

Managing cystinuria involves a combination of lifestyle changes, medications, and, in severe cases, surgical intervention. The following approaches are commonly employed:

Increased Fluid Intake: Drinking ample amounts of fluids helps dilute cystine concentration in the urine, reducing the risk of stone formation.

Dietary Modifications: A low-sodium and low-protein diet may be recommended to decrease the excretion of cystine.

Medications: Certain medications, such as thiol-binding agents like penicillamine or tiopronin, can help bind with cystine in the urine, preventing stone formation.

Alkalinizing agents: Drugs that increase urine pH, such as potassium citrate, may be prescribed to reduce the solubility of cystine and prevent stone formation.

Surgical Intervention: In cases where kidney stones are too large or cause severe obstruction, surgical procedures like shock wave lithotripsy or ureteroscopy may be necessary to remove or break down the stones.

 References:

 Cystinuria: An Overview of Diagnosis and Medical Management, Sanober Sadiq and Onur Cil

Knoll T, Zöllner A, Wendt-Nordahl G, Michel MS, Alken P. Cystinuria in childhood and adolescence: recommendations for diagnosis, treatment, and follow-up. Pediatr Nephrol. 2005 Jan;20(1):19-24. [PubMed]

Reinstatler L, Stern K, Batter H, Scotland KB, Ardekani GS, Rivera M, Chew BH, Eisner B, Krambeck AE, Monga M, Pais VM. Conversion from Cystine to Noncystine Stones: Incidence and Associated Factors. J Urol. 2018 Dec;200(6):1285-1289. [PubMed] 

Disclaimer:

The content provided here is for informational purposes only. This blog is not intended to substitute for medical advice, diagnosis, or treatment. Always seek the advice of a qualified healthcare provider for any questions or concerns you may have regarding a medical condition. Reliance does not endorse or recommend any specific tests, physicians, procedures, opinions, or other information mentioned on the blog.

This article is reviewed by Dr. Rikki Deogade MBBS, Chief Medical officer, NUHM. Dr. Deogade can be consulted on Netmeds.com.