Regarding Hanup disease, all are true except

Hanup disease is a rare genetic condition in which there is a defect of the membrane transpo mechanism for tryptophan, resulting in large losses as a result of intestinal malabsorption and failure of renal reabsorptionHanup disease reflectsImpaired intestinal and renal transpo of tryptophan and other neutral amino acids. Indole derivatives of unabsorbed tryptophan formed by intestinal bacteria are excreted. The defect limits tryptophan availability for niacin biosynthesis and accounts for the pellagra-like signs and symptoms.Which includes mental retardation Reference: Harper biochemistry, 30th edition, page no 308