Hanup disease, limiting amino acid

It&;s an autosomal recessive disease. Absorption of aromatic amino acids from intestine as well as reabsorption from renal tubules are defective Patient improve when put on high protein diet with supplementation of niacin Hence the limiting amino acid is tryptophanRef: DM Vasudevan - Textbook of Biochemistry, 7th edition, page no: 242