Cystinuria

Cystinuria is an autosomal recessive disorder characterized by impaired transport of cystine, lysine, ornithine and arginine in the proximal renal tubule and in the epithelial cells of the gastrointestinal tract. Following recent progress in the genetic understanding of the disease, the traditional classification, based on the excretion of cystine and dibasic amino acids in obligate heterozygotes, may no longer be considered valid. A new classification is therefore needed: type A due to two mutations of SLC3A1 on chromosome 2, and type B due to two mutations of SLC7A9 on chromosome 19. The possibility of a third type, AB, with one mutation on each of the above‐mentioned genes, is left open, but is unlikely. Clinical data show that cystinuria is more severe in males than in females in terms of stone production and early age of onset. The two types of cystinuria (A and B) have a similar outcome. A mild renal failure is present in 17% of patients. Medical treatment of this disorder is possible, but requires a composite approach: urine dilution and alkalization, and the use of drugs to form chemical bonds with the sulphydryl domains of the cystine molecule, which lower the amount of free cystine in the urine. Conclusion: Following new achievements in the genetics of cystinuria, a new classification has been proposed. Cystinuria is more severe in males than in females, but only rarely leads to renal insufficiency. The two types of cystinuria have a similar clinical outcome. A combined medical treatment may be effective in reducing renal stone incidence.