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Hartnup disease
Other Resources UpToDate PubMed

Hartnup disease

Contributors: Bo Hoon Lee MD, Jamie Adams MD, Richard L. Barbano MD, PhD
Other Resources UpToDate PubMed


Hartnup disease is an autosomal recessive metabolic disorder resulting from mutations in SLC6A19 gene on chromosome 5. This gene encodes a sodium-dependent neutral amino acid transporter that is predominantly expressed in the kidneys and intestine. Defects in these transporters lead to impaired absorption of nonpolar amino acids, particularly tryptophan, which is necessary for the production of serotonin, melatonin, and niacin.

Clinical symptoms are highly variable but may appear in infancy with failure to thrive, intermittent ataxia, tremor, and photosensitive dermatitis. Seizures have also been reported.

Others may remain asymptomatic or have symptoms that occur intermittently as "attacks" triggered by poor nutrition, sunlight, illness, stress, and certain medications.

Patients may also have short stature, psychiatric illness, and/or intellectual disability.


E72.02 – Hartnup's disease

80902009 – Neutral 1 amino acid transport defect

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Diagnostic Pearls

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Differential Diagnosis & Pitfalls

  • Pellagra
  • Porphyria (eg, Variegate porphyria, Porphyria cutanea tarda)
  • Citrullinemia
  • Ataxia-telangiectasia syndrome
  • Episodic ataxia (eg, Episodic ataxia type 2)
  • Systemic lupus erythematosus
  • Xeroderma pigmentosum
  • Carcinoid syndrome
  • Mitochondrial disorders (eg, Pyruvate carboxylase deficiency)

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Last Reviewed:10/22/2018
Last Updated:06/19/2022
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Hartnup disease
A medical illustration showing key findings of Hartnup disease : Diplopia, Hyperreflexia, Hypotonia, Mental status alteration, Photosensitivity, Episodic ataxia
Copyright © 2024 VisualDx®. All rights reserved.