Hartnup’s disease [Hartnup, family name of first patients diagnosed in England, 1956] , a rare autosomal-recessive genetic metabolic disorder characterized by pellagra-like skin lesions, transient cerebellar ataxia, and hyperaminoaciduria. It is caused by defects in intestinal absorption and renal reabsorption of neutral amino acids. Bacterial degradation of unabsorbed amino acids in the gut leads to the absorption of breakdown products and their appearance in urine; the unavailability of tryptophan leads to a deficiency of niacin, the antipellagra vitamin. Common symptoms of the disease are dry, scaly, well-circumscribed skin lesions; glossitis; stomatitis; diarrhea; psychiatric problems; and pronounced photosensitivity. Brief exposure to the sun may cause erythema, edema, and vesiculation. Treatment consists of oral nicotinamide, a high-protein diet containing proteins composed of more easily absorbed small peptides, and avoidance of sun exposure.
