<prompt> The aminoacid excreted in Hartnups disease is -ArginineHydroxyprolineTryptophanProline  <response>: Ans. is c i.e., Tryptophan Hartnups disease is caused by a defect of a neutral aminoacid transporter which is specific for tryptophan absorption along intestine and tryptophan reabsorption along renal tubules. Tryptophan malabsorption leads to tryptophan deficiency As tryptophan is necessary for formation of niacin, Hartnups disease presents with niacin deficiency manifestations or pellagra. Photosensitive Dermatitis Diarrhoea Psychiatric manifestations - anxiety, mood changes, delusions, hallucinations As niacin is necessary for insertion of neutral aminoacid transporters into the renal tubules, Hartnups disease presents with aminoaciduria . There is increased excretion of neutral aminoacids like : Tryptophan Isoleucine Phenyalanine Histidine Leucine Lysine Characteristically in aminoaciduria due to hartnup s disease, levels of proline, hydroxyproline and arginine levels are normal. This differentiates Hartups disease aminoaciduria from fanconis syndrome Onset of presentation is variable. Infants with Hartnups disease present with failure to thrive, ataxia, nystagmus. As when tryptophan gets oxidised, the indole ring is released, Obermeyers test or test for urinary Indican is positive. 