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
Hanup's disease is associated with increased urinary excretion of: 
Select and explain. 
A. Tryptophan, B. Ornithine, C. Glycine, D. Cystine
A: Tryptophan
Answer: A: Tryptophan 
Explanation: Hanup's disease is characterized by low plasma levels of tryptophan and other neutral amino acids and their elevated urinary excretion