ABSTRACT
Many patients with Hartnup disease are asymptomatic. The single constant phenotypic feature is the unusual aminoaciduria in which a large group of neutral -amino acids are excreted in large quantities. The pattern was first recognized in paper partition chromatograms [1-3], but it is also clearly recognizable on electrophoresis (Figure 72.1) and on quantitative analysis of the amino acids of the urine in the amino acid analyzer (Figure 72.2). Deficient activity of a sodium-dependent transport system, which controls the absorption of these amino acids at the brush-border of the intestinal and renal epithelium, leads to the phenotype. The aminoaciduria is generalized, but it differs from the usual nonspecific generalized aminoaciduria in that glycine and the amino acids, proline and hydroxyproline, are not excreted in unusual quantity. The amino acids excreted in greatest quantity are those, excluding glycine, that are found in largest quantity in normal urine – alanine, glutamine, serine and histidine. Amino acids, many of them essential, which are excreted in very small quantities in normal urine but in prominent amounts in the urine of patients with Hartnup
disease, include leucine, isoleucine, valine, threonine, phenylalanine, tyrosine and tryptophan. The tryptophanuria may be missed if the patient is studied only by column chromatography on the amino acid analyzer because tryptophan is destroyed by the conditions of analysis. Asparagine is also
excreted in increased quantities, but this compound is not usually separated from glutamine by the amino acid analyzer. It is readily shown in paper chromatograms. The concentrations of these amino acids in the blood are normal or somewhat reduced [4].
