Inborn Errors of Tryptophan Metabolism

Hartnup disease is a rare genetic condition in which there is a defect of the membrane transport mechanism for tryptophan and other large neutral amino acids. The result is that the intestinal absorption of free tryptophan is impaired, although dipeptide absorption is normal. There is a considerable urinary loss of tryptophan (and other amino acids) as a result of the failure of the normal reabsorption mechanism in the renal tubules - renal aminoaciduria. In addition to neurological signs that can be attributed to a deficit of tryptophan for the synthesis of serotonin in the central nervous system, the patients show clinical signs of pellagra, which respond to the administration of niacin. 

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Tl. Tada, K., Ito, H., Wada, Y., and Arakawa, T., Congenital tryptophanuria with dwarfism ( H -disease-like clinical features without indicanuria and generalized aminoaciduria) —a probably new inborn error of tryptophan metabolism. Tohoku J. Exp. Med. 80, 118-134 (1963). 

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