Cystinuria

Cystinuria is an inherited disorder of the transport of the amino acid cystine, resulting in cystinuria and the formation of cystine stones.

Urinary Obstruction

Obstruction of the urinary tract increases pressure on the ureter and kidney, causing dilation of the ureter and compression of the kidney.

Urinary tract obstruction also leads to stagnant urine, which increases the risk of urinary tract infections.

Effect on the Kidney

The pressure on the kidneys and urinary infections can cause damage, leading to renal insufficiency and end-stage kidney disease requiring renal dialysis or a transplant.

Cystine in the Urine

Cystine, along with other amino acids, precipitates out of urine and forms stones in the kidney, ureter, bladder, or anywhere in the urinary tract. Cystine is the least soluble of all naturally occurring amino acids.

The cystine stones obtained from the kidney of a young woman were crushed and removed through percutaneous nephrolithotripsy, a procedure specifically for cystinuria.

Impact of Cystine Stones

While small stones are passed in the urine, larger stones cause kidney nephrolithiasis, obstructing urine outflow. Medium-sized stones can block urine flow in the ureter.

Causes of Cystinuria

Cystinuria is caused by defective transport of cystine and other amino acids through kidney and intestinal cells.

Prevalence of Cystinuria

Cystinuria is one of the more common genetic disorders, affecting approximately 1 in 7,000 people.

Cystinuria is the most common defect in amino acid transport.

Transport Defects

Transport systems in the body allow molecules to pass across cell membranes through receptors and carrier proteins. Defects in these systems can lead to various diseases, including cystinuria.

Hereditary Nature of Cystinuria

Cystinuria is inherited as an autosomal recessive trait. There are three types of cystinuria, each inherited differently.

Symptoms of Cystinuria

Signs and symptoms of cystinuria are directly or indirectly caused by the formation of stones and include hematuria, flank pain, renal colic, obstructive uropathy, and urinary tract infections.

Laboratory Findings

The key laboratory finding in cystinuria is elevated cystine levels in the urine, along with increased levels of other structurally similar amino acids. These findings indicate aminoaciduria.

Diagnosis of Cystinuria

Early diagnosis of cystinuria is crucial for effective treatment and prevention of complications. Failure to diagnose and treat cystinuria promptly can result in significant morbidity and mortality.

Treatment for Cystinuria

High Fluid Intake: Increasing urine volume through high fluid intake helps prevent cystine stone formation. A minimum daily intake of 4 liters is recommended, with 5 to 7 liters per day being ideal.

Alkalizing the Urine: Alkalizing the urine using substances like sodium bicarbonate has been attempted to prevent cystine stone formation, but this can lead to other types of kidney stones.

Penicillamine: Treatment with penicillamine can help dissolve cystine stones and prevent new stone formation. Side effects of penicillamine are usually mild.

Percutaneous Nephrolithotripsy (PCNL): PCNL is a procedure used to remove dense cystine stones that cannot be broken up with shock waves. It involves puncturing the kidney through the skin and removing the stones using specialized instruments under X-ray guidance.