Niacin, absorption phosphate

Hartnup s disease. There is a defect in the epithelial transport of neutral amino acids (e.g., tryptophan) leading to poor absorption and excess excretion of these amino acids. Clinical signs resemble those of niacin deficiency (tryptophan is a precursor of niacin), namely the 3 D s Diarrhea, Dementia, Dermatitis. The condition responds to nicotinamide administration. Fan-coni s syndrome is a more generalized defect in molecular transport, involving a multitude of amino acids, glucose, calcium, phosphate, proteins, and other molecules. There may be decreased growth and rickets. 

Hartnup disease, an autosomal recessive trait that interferes with the absorption of tryptophan, and carcinoid syndrome in which the amino acid is preferentially oxidized to 5-hydroxytryptophan and serotonin. Prolonged treatment with the drug isoniazid, which competes with pyridoxal 5 -phosphate (a vitamin Be-derived coenzyme required in the tryptophan-to-niacin pathway), also reduces the conversion of tryptophan to niacin. Oral contraceptives that contain high doses of estrogen increase tryptophan conversion efficiency (Braidman and Rose 1971). 

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