[Cystinuria: from diagnosis to follow-up]

Cystinuria is an autosomal recessive disorder characterized by an impaired transport of cystine and dibasic aminoacids, lysine, arginine and ornithine in the proximal renal tubule and in the epithelial cells of the gastrointestinal tract. Recurrent cystine nephrolithiasis is the main clinical feature. Mutations in SLC3A1 and/or SLC7A9 genes, which are encoding respectively the rBAT and the b(0,+)AT proteins of the amino acid transport system, are responsible of this disorder thus inducing a high dibasic amino acid excretion. Diagnostic is based on stone analysis by infrared spectroscopy or microscopic examination of urine which may reveal typical cystine crystals. Quantitative cystine excretion, which may be assessed by aminoacid chromatography, is higher in cystinic patients. Molecular approach can identify mutations which are responsible of this pathology. Medical treatment is mainly based on hydratation and urine alkalinisation, with the addition of thiol derivative only in refractory cases. Follow-up based on pH and specific gravity determination in urine samples and cystine crystal volume measurement are used to optimally monitor the medical treatment of cystinuric patients. Even with medical management, long-term outcome is poor due to insufficient efficacy and low patient compliance. Many patients suffer from renal insufficiency as a result of recurrent stone formation and repeated surgical procedures.