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.
Most people show no symptoms. If symptoms do occur, they usually appear in childhood and may include:
Nervous system (neurologic) problems, such as abnormal muscle tone
Red, scaly skin rash, usually when skin is exposed to sunlight
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.
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
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.
There are usually no complications. When they occur, complications may include:
Changes in skin color that are permanent
Mental health problems
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.
Genetic counseling may help prevent some cases. Eating a high-protein diet may prevent amino acid deficiencies that cause symptoms.
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.
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.