During a screening program for aminoaciduria, a previously not described disorder of renal tubular transport of amino acids was found in two mentally retarded infants. Urinary analyses of amino acids revealed an excessive excretion of both proline and glycine with a normal range of excretion of the other amino acids. Proline and glycine in sera from the two patients were found to be of normal or subnormal levels. Renal clearance rates of proline and glycine were highly elevated in the patients. It was, therefore, suggested that hyperprolinuria associated with hyperglycinuria observed in the patients was of renal type. Genetic aspects for renal transport of proline and glycine were discussed.
