Cystinuric heterozygotes and cystine-loading.

During routine screening procedures for amino acid disorders by thin layer chromatography, performed in a children's psychiatric hospital, we detected 6 children who excreted excessive amounts of dibasic amino acids. The probands, their siblings and parents and 11 controls (29 subjects in all) were loaded with cystine. On the basis of the urinary excretion after the loading we distinguished normal subjects from cystinuric heterozygotes, which we further subdivided in heterozygotes type II and III by the corresponding serum response.