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Hartnup disease

MIM.234500 eM.derm/713

Friday 1 August 2008

Definition: Hartnup disease is an autosomal recessive genetic metabolic disorder in the absorption of neutral amino acids, particularly tryptophan.

Tryptophan can be 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.


- failure to thrive
- photosensitivity
- intermittent ataxia
- nystagmus
- tremor


Nicotinamide is necessary for neutral amino acid transporter production in the proximal renal tubules found in the kidney, and intestinal mucosal cells found in the small intestine. Therefore, a symptom stemming from this disorder results in increased amounts of amino acids in the urine.

See also

- pellagra (also caused by low nicotinamide)