This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Metabolism of which of the following amino acid is at fault in Hanup's disease: 
Select and explain. 
A. Tryptophan, B. Sulfur amino acids, C. Glycine, D. Histidine
A: Tryptophan
Answer: A: Tryptophan 
Explanation: Abnormal metabolism of amino acids and conditions Hanup's disease is a hereditary disorder of tryptophan metabolism Sulfur amino acids (methionine, cysteine and cystine) metabolism disorder results in cystinuria, cystinosis, homocystinuria and cystathionuria Disorder of glycine metabolism results in glycinuria and primary hyperoxaluria Defect in metabolism of histidine results in histidinemia