Hartnup disease

Hartnup disease (also known as "Pellagra-like dermatosis," and "Hartnup disorder") is an autosomal recessive metabolic disorder affecting the absorption of nonpolar amino acids (particularly tryptophan that can be, in turn, converted into Serotonin, Melatonin and Niacin). Niacin is a precursor to nicotinamide, a necessary component of NAD+. The causative gene, SLC6A19, is located on chromosome 5. The defective gene controls the absorption of certain amino acids from the intestine and the reabsorption of those amino acids in the kidneys. Consequently, a person with Hartnup disease cannot absorb amino acids properly from the intestine and cannot reabsorb them properly from tubules in the kidneys. Excessive amounts of amino acids, such as...