This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Inborn Errors of Metabolism, Subject name: Pediatrics
In Hartnup disorder, metabolism of which of the following amino acids is affected? 
Select and explain. 
A. Tyrosine, B. Tryptophan, C. Phenylalanine, D. Homocysteine
B: Tryptophan
Answer: B: Tryptophan 
Explanation: b. Tryptophan(Ref: Nelson's 20/e p 648-649)In Hartnup disorder, there is a defect in transport of monoamino-monocarboxylic amino acids (neutral amino acids), including tryptophan, by intestinal mucosa & renal tubules due to mutation of SLC6A19 gene located on chr 5pl 5