BACKGROUND Cystinuria is an inherited autosomal recessive disorder, characterised by the impaired reabsorbtion of cystine, lysine, ornithine and arginine in the proximal tubule with an increased urinary excretion, resulting in a risk of renal stone formation because of the low solubility of cystine in urine. The estimated rate is 1:15000–20000 live births. This disease is caused by mutations of the genes SLC3A1 (2 P21) and/or SLC7A9 (19q13.11), encoding heavy subunit of a transepithelial dibasic aminoacid transport protein, responsible of type A and B, respectively. The main goal of the treatment is to prevent the recurrent urinary stone formation, and it’s based on hydration therapy, urine alkalinization and cystine chelating drugs. When medical treatment is ineffective, surgery should be considered.

CASE REPORT An 8 years old girl was referred to our hospital for recent UTI and low back pain on both sides. Renal ultrasound showed kidney stones on both sides and a grade II of hydronephrosis on the right. A metabolic alkalosis and a low urinary excretion of citrate were discovered. Investigations revealed urinary levels of cystine (418 mmol/molcreat U), lisine, arginine and ornithine upper normal range. The patient has been treated with potassium citrate, antibiotic and hiperhydration. By a molecular analysis a compound heterozygosity for a mutation of the gene SLC3A1 was discovered. Both parents were asymptomatic heterozygous carriers of the same mutation. In a long-term follow up a clinical improvement was assessed, in fact the low back pain disappeared. In addition in different occasions, an urine alkalinization was documented, while the levels of urinary cystine were still high. For this reasons, the patient started the treatment with tiopronin.

Conclution Frequent clinical, laboratory tests and ultrasound follow-up is needed to encourage patient compliance and assess efficacy and tolerance of treatment. If there is not an improvement, a cysteine chelation treatment should be evaluated, despite its side effects, or surgery if medical treatment is ineffective.