Prevalence is estimated at 1 in 7000 live births, and as much as 2% of adult nephrolithiasis is attributable to cystine stones. In pediatric populations, as much as 5% of stone formation is attributed to cystinuria.
Affected individuals have impaired transtubular reabsorption of dibasic amino acids, including cystine, ornithine, lysine, and arginine, in the proximal tubule. While cystine has low solubility at normal urinary pH, the other dibasic amino acids are quite soluble and consequently do not result in precipitation or stone formation. However, the excessive urinary cystine excretion leads to cystine nephrolithiasis. Clinically, cystine stones manifest in the same way as other forms of nephrolithiasis with hematuria and colicky flank pain radiating to the groin.
Because cystinuria is a more common form of nephrolithiasis in the pediatric population, there should be high clinical suspicion for cystinuria in a patient who presents with a first episode of stones in adolescence or earlier. While stones can present as early as in infancy, particularly in homozygotes, the median age of onset is 12 years of age. Although there is little explanation pathophysiologically, cystinuria appears to result in more frequent symptomatic episodes in men.
For more information, see OMIM.
E72.01 – Cystinuria
85020001 – Cystinuria
- Pyelonephritis – Fever uncommon in uncomplicated nephrolithiasis.
- Loin pain-hematuria syndrome
- Renal cell carcinoma
- Ectopic pregnancy – Beta-human chorionic gonadotropin (bhCG) should be checked in any woman who has a possibility of pregnancy.
- Testicular tumors
- Ovarian torsion or rupture
- Biliary colic and cholecystitis – Hematuria is not a feature of these diseases.
- Mesenteric ischemia – Hematuria is not a feature of this disease.
- Opioid use disorder – Patients may feign the symptoms of nephrolithiasis in order to obtain narcotics.