<unk>  can develop according to several mechanisms, classically as a result of niacin (vitamin B3) deficiency, which results in decreased nicotinamide adenine dinucleotide (NAD). Since NAD and its phosphorylated NADP form are cofactors required in many body processes, the pathological impact of<unk>  is broad and results in death if not treated. The first mechanism is simple dietary lack of niacin. Second, it may result from deficiency of tryptophan, an essential amino acid found in meat, poultry, fish, eggs, and peanuts that the body uses to make niacin. Third, it may be caused by excess leucine, as it inhibits quinolinate phosphoribosyl transferase (QPRT) and inhibits the formation of niacin or nicotinic acid to nicotinamide mononucleotide (NMN) causing<unk>  like symptoms to occur. Some conditions can prevent the absorption of dietary niacin or tryptophan and lead to<unk> . Inflammation of the jejunum or ileum can prevent nutrient absorption, leading to<unk> , and this can in turn be caused by Crohn's disease. Gastroenterostomy can also cause<unk> . Chronic alcoholism can also cause poor absorption which combines with a diet already low in niacin and tryptophan to produce<unk> . Hartnup disease is a genetic disorder that reduces tryptophan absorption, leading to<unk> . Alterations in protein metabolism may also produce<unk> -like symptoms. An example is carcinoid syndrome, a disease in which neuroendocrine tumors along the GI tract use tryptophan as the source for serotonin production, which limits the available tryptophan for niacin synthesis. In normal patients, only one percent of dietary tryptophan is converted to serotonin; however, in patients with carcinoid syndrome, this value may increase to 70%. Carcinoid syndrome thus may produce niacin deficiency and clinical manifestations of<unk> . Anti-tuberculosis medication tends to bind to vitamin B6 and reduce niacin synthesis, since B6 (pyridoxine) is a required cofactor in the tryptophan-to-niacin reaction. Several therapeutic drugs can provoke<unk> . These include the antibiotics isoniazid, which decreases available B6 by binding to it and making it inactive, so it cannot be used in niacin synthesis, and chloramphenicol; the anti-cancer agent fluorouracil; and the immunosuppressant mercaptopurine.
Pellagra
Pemphigus
Koilonychia
Kwashiorkor
Melanonychia
Porphyria
Crepitus
Photodermatitis