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Hartnup disorder

Definition

Hartnup disorder is an inherited metabolic condition that involves the transport of certain amino acids (for example, tryptophan and histidine) in the small intestine and kidneys.

Causes

Hartnup disorder is possibly the most common metabolic condition involving amino acids. It is an inherited condition. A child must inherit a copy of the defective gene from both parents in order to be seriously affected.

The condition most often appears between ages 3 to 5 years.

Symptoms

Most people show no symptoms. If symptoms do occur, they most often appear in childhood and may include:

  • Diarrhea
  • Mood changes
  • Nervous system (neurologic) problems, such as abnormal muscle tone
  • Red, scaly skin rash, usually when skin is exposed to sunlight
  • Sensitivity to light (photosensitivity)
  • Short stature
  • Uncoordinated movements

Exams and Tests

A urine test that checks for high levels of "neutral" amino acids and normal levels of other amino acids may be done for this disorder.

Health care providers can test for the gene that causes Hartnup disease, SLC6A19. Biochemical tests are also available.

Treatment

Treatments include:

  • Avoiding sun exposure by wearing protective clothing and using a sunscreen with a protection factor of 15 or higher
  • Eating a high-protein diet
  • Taking supplements containing nicotinamide
  • Undergoing mental health treatment, such as taking antidepressants or mood stabilizers, if mood swings or other mental health problems occur

Outlook (Prognosis)

Most people with this disorder can expect to live a normal life with no disability. Rarely, there have been reports of severe nervous system disease and even deaths in families with this disorder.

Possible Complications

In most cases, there are no complications. Complications when they occur may include:

  • Changes in skin color that are permanent
  • Mental health problems
  • Rash
  • Uncoordinated movements

Nervous system symptoms can most often be reversed. However, in rare cases they can be severe or life threatening.

When to Contact a Medical Professional

Call for your provider if you have symptoms of this condition, especially if you have a family history of Hartnup disorder. Genetic counseling is recommended if you have a family history of this condition and are planning a pregnancy.

Prevention

Genetic counseling may help prevent some cases. Eating a high-protein diet may prevent amino acid deficiencies that cause symptoms.

References

Gibson KM, Pearl PL. Inborn errors of metabolism and the nervous system. In: Daroff RB, Jankovic J, Mazziotta JC, Pomeroy SL, eds. Bradley's Neurology in Clinical Practice. 7th ed. Philadelphia, PA: Elsevier; 2016:chap 91.

Kliegman RM, Stanton BF, St. Geme JW, Schor NF. Defects in metabolism of amino acids. In: Kliegman RM, Stanton BF, St. Geme JW, Schor NF, eds. Nelson Textbook of Pediatrics. 20th ed. Philadelphia, PA: Elsevier; 2016:chap 85.

Review Date:8/16/2016
Reviewed By:Anna C. Edens Hurst, MD, MS, Assistant Professor in Medical Genetics at the University of Alabama, Birmingham, AL. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.

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Outcome Data

No data available for this condition/procedure.

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