Which of the following clinical laboratory observations is suggestive of Hartnup disease?

Ans. D. High fecal levels of tryptophan and indole derivativesa. In Hartnup disease, a defect in the transport process for neutral amino acids is most pronounced in intestinal and renal transport. Neutral aminoaciduria is observed as well as increased fecal excretion of indole derivations due to bacterial conversion of unabsorbed dietary tryptophan.b. Pellagra-like symptoms can be seen-because of the lack of tryptophan for niacin biosynthesis. Hyper ammonia can be caused by a variety of urea cycle defects including carbamoyl phosphate synthase I deficiency (237300).c. The high levels of NH/ in the blood lead to very high levels of glutamine synthesis that may well be responsible for the subsequent brain damage. Deficiency of liver phenylalanine hydroxylase causes phenylketonuria . Consequently, high levels of phenylalanine are not converted to tyrosine.d. Phenylalanine and its metabolites accumulate in blood, leading to mental retardation if infants are not placed on a phenylalanine-restricted diet. Urine darkens upon standing because of the high levels of Homogentisate that result from of a deficiency in Homogentisate oxidase in the disease alkaptonuria (203500). This is a deficiency in the pathway of tyrosine breakdown.