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Hartnup disorder

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, incidence, and risk factors

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 usually starts between ages 3 - 5 years.

Symptoms

Most people show no symptoms. If symptoms do occur, they usually 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

Signs 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 of factor 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

Expectations (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.

Complications

There are usually no complications. When they occur, complications may include:

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

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

Calling your health care provider

Call for an appointment with your health care 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

Rezvani I, Melvin JJ. Defects in metabolism of amino acids. In: Kliegman RM, Stanton BF, St. Geme J, Behrman RE, eds. Nelson Textbook of Pediatrics. 19th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 79.

Updated: 7/8/2012

Chad Haldeman-Englert, MD, FACMG, Wake Forest School of Medicine, Department of Pediatrics, Section on Medical Genetics, Winston-Salem, NC. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M. Health Solutions, Ebix, Inc.


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