<prompt> A 2-year old male child presents with pellagra like lesions with passage of amino acids in urine. In the family, out of 4 siblings, two are having similar symptoms with two normal siblings and parents are not affected. Most likely diagnosis is:PhenylketonuriaAlkaptonuriaMaple syrup urine diseaseHanup disease  <response>: Ans. d. Hanup disease. Hanup Disease Genetic Defect :A rare autosomal recessive disorder that results in the mutation of a sodium-dependent transpo channel of neutral amino acids ie, tryptophan. Pathophysiology :The neutral amino acid transpo channel is present in both the proximal tubule of the nephron and the brush border of the small intestine . If this transpo channel is defective, neutral amino acids cannot be absorbed in the intestine or reabsorbed by the kidney after filtration, thereby resulting in a relative deficiency of the neutral amino acids, such as tryptophan . If the body is deficient in tryptophan a precursor for niacin, symptoms can arise that mimic niacin deficiency ie, pellagra. Clinical Manifestations Symptoms appear intermittently and tend to decrease with age. Symptoms include a photosensitive dermatitis that affects face, neck, and extensor surfaces of limbs and neurologic signs headaches; personality disturbances ; photophobia; mental retardation; cerebellar ataxia . Lab findings: Renal aminoaciduria ; indoles in the urine. Treatment : Nicotinic acid supplements. 