Pellagra despite adequate tryptophan and niacin intake

THE CONTEXT

Disease-related defects in tryptophan handling or diversion of its metabolism can cause pellagra despite an apparently adequate dietary intake.

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Hartnup disease is a rare genetic condition involving a defect in the membrane transport mechanism for tryptophan.

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The transport defect causes large tryptophan losses through intestinal malabsorption and failure of renal reabsorption.

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The passage describes enterochromaffin tumor cells that synthesize 5-hydroxytryptamine.

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Overproduction of 5-hydroxytryptamine may account for as much as 60% of the body's tryptophan metabolism.

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This diversion of tryptophan away from NAD synthesis can cause pellagra.

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