In Hartnup disorder, metabolism of which of the following amino acids is affected?

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