In Hartnup's disease which of the following is excreted in the urine:

Ans. (c) TryptophanRef: Harper's Biochemistry, 30th ed. pg. 308, 557; Harrisons, 19th ed. pg. 435e-2* Hartnup disease is an autosomal recessive disorder caused by impaired neutral amino acid transport in the apical brush border membrane of the small intestine and the proximal tubule of the kidney.* Patients of hartnup disease present with pellagra like skin eruptions, cerebellar ataxia, and gross aminoaciduria.* Amino acids which are retained within the intestinal lumen due to impaired transport, are converted by bacteria to indolic compounds that can be toxic to the CNS. Amino acid like Tryptophan is converted to indole in the intestine.* Following absorption, indole is converted to 3-hvdroxyindole (i.e, indoxyl, indican) in the liver, where it is conjugated with potassium sulfate or glucuronic acid. Subsequently, it is transported to the kidneys for excretion (i.e, indicanuria).* Other tryptophan degradation products which are excreted in urine are: kynurenine and serotonin.* In these patients Tubular renal transport is also defective, contributing to gross aminoaciduria.