Definition:

Cystinuria is an inherited disorder of re-absorptive transport of cystine and the dibasic amino acids ornithine, arginine and lysine in the proximal tubule and small intestine. Diagnostically, urinary levels of dibasic amino acids lysine, arginine, and ornithine, and most prominently, of cystine are constantly elevated. Plasma levels of these amino acids in general are at the lower end of the normal range. Patients with cystinuria often present with nephro- or urolithiasis at almost at any age with a clear preference in childhood due to elevated urinary cystine. Early diagnosis is important, as it allows prevention or diminution of kidney stones. Mutations in either interacting subunit SLC3A1 (rBAT) or SLC7A9 (b0,+AT) cause cystinuria. Cystinuria due to mutations in SLC3A1 is an autosomal recessive trait, whereas mutations in SLC7A9 can be seen as an autosomal dominant trait.