Hartnup disease

Definition

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

Description

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 & 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.

Diagnosis

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).

Treatment

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.

Prognosis

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

Prevention

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.

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.

Further Reading

For Your Information

Books

• "Hartnup disease." In Cecil Textbook of Medicine, 20th ed., Vol. 1, edited by J. Claude Bennett and Fred Plum. Philadelphia, PA: W.B. Saunders Company, 1996.
• "Hartnup disease." In The Merck Manual of Diagnosis and Therapy, edited by Robert Berkow. Rahway, NJ: Merck Research Laboratories, 1992.
• "Neutral aminoaciduria: Hartnup disease." In Internal Medicine, 5th ed., edited by Jay H. Stein. St. Louis, MO: Mosby, 1998.
• "Selected disorders of amino acid transport." In Harrison's Principles of Internal Medicine, 14th ed., Vol. 2, edited by Anthony S. Fauci, et al. New York, NY: McGraw-Hill, 1998.

  Organizations

• The National Organization for Rare Disorders, Inc. P.O. Box 8923, New Fairfield, CT 06812-8923. (203) 746-6518. (800) 999-6673. http://www.nord-rdb.com/~orphan.
• NIH/National Institute of Diabetes, Digestive and Kidney Diseases. Building 31, Room 9A04, 31 Center Drive, Bethesda MD 20892-2560. (301) 496-3583.

  Other

• Hartnup disorder.http://www.ncbi.nlm.nih.gov.
• Nephrology: Hartnup disease. http://www.medstudents.com.br/nefro/nefro3.htm.

Gale Encyclopedia of Medicine. Gale Research, 1999.