This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Tryptophan metabolism detail, Subject name: Biochemistry
The transpoer gene defective in Hanup's disease: 
Select and explain. 
A. SLC 6A 19, B. SLC 6A 18, C. SLC 36 A2, D. SLC 7A7
A: SLC 6A 19
Answer: A: SLC 6A 19 
Explanation: Hanup's disease is due to defective neutral amino acid transpoer. The SLC6A19 is neutral amino acid transpoer involved in the transpo of neutral amino acids like tyrptophan. Tryptophan is the precursor of Niacin (vitamin B3) Hanup'sdisease is associated with pellagra. Extra edge:- Soluble carrier family (SLC) proteins are transmembrane proteins involved in facilitated diffusion and secondary active transpo. Nomenclature of SLC protein is: SLCnXm SLC stands for SoLuteCarrier n = an integer representing a family (e.g., 1-52) X = a single letter (A, B, C, ...) denoting a subfamily m = an integer representing an individual family member (isoform).