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Hartnup's disease
Last reviewed: 05.07.2025
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Hartnup disease is a rare disorder associated with abnormal reabsorption and excretion of tryptophan and other amino acids. Symptoms of Hartnup disease include rash, CNS abnormalities, short stature, headaches, and fainting and collapse. Diagnosis is based on detecting high levels of tryptophan and other amino acids in the urine. Preventive treatment includes niacin or niacinamide, and nicotinamide is given during attacks.
What causes Hartnup disease?
Hartnup disease is inherited in an autosomal recessive manner. Decreased absorption of tryptophan, phenylalanine, methionine, and other monoaminomonocarboxylic amino acids in the small intestine develops. Accumulation of unabsorbed amino acids in the gastrointestinal tract increases their metabolism by bacterial flora. Some products of tryptophan degradation, including indoles, kynurenine, and serotonin, are absorbed in the intestine and appear in the urine. Renal reabsorption of amino acids is also impaired, causing generalized aminoaciduria, including all neutral amino acids except proline and hydroxyproline. The conversion of tryptophan to niacinamide is also impaired.
Symptoms of Hartnup disease
Symptoms are almost always preceded by low nutrient intake. Symptoms of Hartnup disease are due to niacinamide deficiency and resemble those of pellagra, especially the rash on exposed areas of the body. Neurological manifestations include cerebellar ataxia and mental disorders. Mental retardation, short stature, headaches, collapse, and fainting are common. Although the disease is present from birth, symptoms may appear in infancy, childhood, or young adulthood. Symptoms may be precipitated by sun exposure, certain medications, or other stresses.
Diagnosis of Hartnup disease
The diagnosis is based on the detection of characteristic disturbances in the excretion of amino acids in the urine. Indoles and other degradation products of tryptophan in the urine are additional evidence of the presence of Hartnup disease.
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Treatment of Hartnup disease
Hartnup disease has a favorable prognosis, and the frequency of attacks usually decreases with age. Attacks can be prevented by maintaining good nutritional status and supplementing the diet with niacin or niacinamide, 50-100 mg orally 3 times a day. An attack that has developed is treated with nicotinamide, 20 mg orally once a day.
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