Hartnup disease

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Hartnup Disease



Hartnup disease is an inherited nutritional disorder with primary symptoms including a red, scaly rash and sensitivity to sunlight.


Hartnup disease was first identified in the 1950s in the Hartnup family in London. A defect in intestines and kidneys makes it difficult to break down and absorb protein in the diet. This causes a condition very similar to pellegra (niacin deficiency). The condition occurs in about one of every 26,000 live births.

Causes and symptoms

Hartnup disease is an in-born error of metabolism, that is, a condition where certain nutrients cannot be digested and absorbed properly. The condition is passed on genetically in families. It occurs when a person inherits two recessive genes for the disease, one from each parent. People with Hartnup disease are not able to absorb some of the amino acids (the smaller building blocks that make up proteins) in their intestines. One of the amino acids that is not well absorbed is tryptophan, which the body uses to make its own form of niacin.
The majority of people with this disorder do not show any symptoms. About 10-20% of people with Hartnup disease do have symptoms. The most prominent symptom is a red, scaly rash that gets worse when the patient is exposed to sunlight. Headache, fainting, and diarrhea may also occur. Mental retardation, cerebral ataxia (muscle weakness), and delirium (a confused, agitated, delusional state) are some of the more serious complications that can occur. Short stature has also been noted in some patients. Although this is an inherited disease, the development of symptoms depends on a variety of factors including diet, environment, and other genetic traits controlling amino acid levels in the body. Symptoms can be brought on by exposure to sunlight, fever, drugs, or other stresses. Poor nutrition frequently precedes an attack of symptoms. The frequency of attacks usually decreases as the patient gets older.


The symptoms of this disease suggest a deficiency of a B vitamin called niacin. A detailed diet history can be used to assess if there is adequate protein and vitamins in the diet. The diagnosis of Hartnup disease is confirmed by a laboratory test of the urine which will contain an abnormally high amount of amino acids (aminoaciduria).


The vitamin niacin is given as a treatment for Hartnup disease. The typical dosage ranges from 40-200 mg of nicotinamide (a form of niacin) per day to prevent pellagra-like symptoms. Some patients may require dietary supplements of tryptophan.
Eating a healthy, high protein diet can relieve the symptoms and prevent them from recurring.


The prognosis for a healthy life is good once the condition has been identified and treated.

Key terms

Amino acids — Proteins are made up of organic compounds called amino acids. The human body uses amino acids to build and repair body tissue. The body can make some of its own amino acids from other nutrients in the diet; these are called non-essential amino acids. Essential amino acids are those that cannot be made by the body but must be consumed in the diet. Animal proteins (like meat, eggs, fish, and milk) provide all of the amino acids.
Aminoaciduria — A condition confirmed by laboratory tests where high levels of amino acids are found in the urine.
Pellegra — A condition caused by a dietary deficiency of one of the B vitamins, called niacin.
Tryptophan — An essential amino acid that has to consumed in the diet because it cannot be manufactured by the body. Tryptophan is converted by the body to niacin, one of the B vitamins.


Hartnup disease is an inherited condition. Parents may not have the disease themselves, but may pass the genes responsible for it on to their children. Genetic testing can be used to identify carriers of the genes. Symptoms can usually be controlled with a high protein diet, vitamin supplements of niacin, and by avoiding the stresses that contribute to attacks of symptoms.



National Organization for Rare Disorders. PO Box 8923, New Fairfield, CT 06812-8923. (800) 999-6673. http://www.rarediseases.org.
NIH/National Institute of Diabetes, Digestive and Kidney Diseases. Building 31, Room 9A04, 31 Center Drive, Bethesda MD 20892-2560. (301) 496-3583.


"Hartnup disorder." OMIM Homepage, Online Mendelian Inheritance in Man. http://www.ncbi.nlm.nih.gov/Omim.
"Nephrology: Hartnup disease." Medstudents.com. http://www.medstudents.com.
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.

Hartnup disease

a genetically determined disorder of intestinal and renal transport of neutral alpha-amino acids, with pellagra-like skin lesions, transient cerebellar ataxia, constant renal aminoaciduria and other biochemical abnormalities.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.

Hart·nup dis·ease

(hart'nŭp), [MIM*234500]
an autosomal recessively inherited metabolic disorder characterized by aminoaciduria which is due to defective renal tubular transport of neutral α-amino acids; there is increased urinary excretion of tryptophan derivatives caused by defective intestinal absorption and bacterial degradation of unabsorbed tryptophan in the gut; manifestations include pellagralike, light-sensitive skin rash with temporary cerebellar ataxia.
Synonym(s): Hartnup syndrome
Farlex Partner Medical Dictionary © Farlex 2012

Hartnup disease

A clinically variable autosomal recessive disorder (OMIM:234500) characterised by a marked increase in renal and intestinal excretion of neutral amino acids. Individuals may be asymptomatic or develop a photosensitive pellagra-like rash, cerebellar ataxia, and other neurological or psychiatric features.

Molecular pathology
Caused by defects of SLC6A19, which encodes a protein that actively transports neutral amino acids (especially leucine) across the apical membrane of intestinal and renal epithelial cells.
Segen's Medical Dictionary. © 2012 Farlex, Inc. All rights reserved.

Hart·nup dis·ease

, Hartnup syndrome (hărt'nup di-zēz', sin'drōm)
A congenital metabolic disorder consisting of aminoaciduria due to a defect in renal tubular absorption of neutral α-amino acids and urinary excretion of tryptophan derivatives, which occurs because defective intestinal absorption leads to bacterial degradation of unabsorbed tryptophan in the gut; characterized by a pellagralike, light-sensitive skin rash with temporary cerebellar ataxia.
Medical Dictionary for the Health Professions and Nursing © Farlex 2012

Hartnup disease

A rare genetic metabolic disease in which the amino acid tryptophan is not normally absorbed causing a PELLAGRA-like syndrome. The condition is named after Edward Hartnup who was found to suffer from the disorder.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005


surname of the English family first described with this condition.
Hartnup disease - autosomal recessive metabolic disease characterized by skin rash, emotional lability, unsteady gait, and various neurological symptoms. Synonym(s): Hartnup syndrome
Hartnup syndrome - Synonym(s): Hartnup disease
Medical Eponyms © Farlex 2012

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