[The hyperaminoacidurias with special reference to cystinuria].

Increased urinary excretion of free amino acids is a sign which requires determination of the underlying cause. Physiological aspects of tubular transport with emphasis on the role played by transport proteins or carriers are briefly discussed. Subsequently we present a resumptive classification. In prerenal hyperaminoaciduria the urinary excretion of amino acids just reflects the error in amino acid metabolism. Depending on tubular reabsorption of the amino acid involved in the metabolic error three types can be distinguished: the overflow, the competitive and the non-threshold hyperaminoacidurias. Renal hyperaminoaciduria can either be specific for individual or group-related amino acids, or generalized involving all amino acids. With the exception of classical cystinuria the various hyperaminoacidurias have more theoretical than clinical importance. Generalized hyperaminoaciduria is always a symptom of severe tubular disturbance which can be produced by various metabolic diseases, intoxications or deficiency states. Finally we present our experience in the treatment of cystinuria with mercaptopropionyl-glycine.