Pellagra is a vitamin deficiency disease most frequently caused by a chronic lack of niacin (vitamin B₃ or synonym: vitamin PP (from: Pellagra Preventing factor)) in the diet. It can be caused by decreased intake of niacin or tryptophan, and possibly by excessive intake of leucine. It may also result from alterations in protein metabolism in disorders such as carcinoid syndrome or Hartnup disease. A deficiency of the amino acid lysine can lead to a deficiency of niacin, as well.