Pellagra is caused by -

Ans. is 'a' i.e., Hartnup's diseaseHartnup's disease* It is a defect of neutral aminoacid transporter which is specific for tryptophan. This transporter is responsible for tryptophan absorption along intestine as well as tryptophan reabsorption across renal tubules.* When tryptophan is not absorbed, tryptophan can not be converted into niacin (Niacin is endogenously synthesised from tryptophan). Hence it presents as pellagra.* As the transporter is also related to tryptophan reabsorption along renal tubules, tryptophan will be lost in the urine. Hence it presents as aminoaciduria.