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At a glance

Hartnup disease manifests during infancy with variable clinical presentation that includes failure to thrive, photosensitivity, intermittent cerebellar ataxia, nystagmus, and tremor. Pellagra-like skin eruption and gross aminoaciduria completed the description.


H Disease; Hart Syndrome; Hartnup Disorder or Syndrome; Pellagra-Cerebellar Ataxia-Renal Aminoaciduria Syndrome; Tryptophan Pyrrolase Deficiency; Pellagra-like Dermatosis.


Metabolic disorder of amino acids named after the first family in which the disorder was found (Hartnup family of London).


Approximately 1:15,000 live births in the United States (similar to phenylketonuria); 1:18,000 to 42,000 live births in the rest of the world. No racial or sex predilection.

Genetic inheritance

Autosomal recessive (probably a monogenic defect that interacts with polygenic and environmental factors, giving a wide clinical spectrum). Gene located on 5p15.


Defect of transport of neutral alpha-amino acids (mainly tryptophan) across the intestinal mucosa and renal tubules as a result of defective tryptophan pyrrolase. Retained amino acids are converted by intestinal bacteria to indolic compounds, which have a cerebral toxicity.


Hartnup disease is a disorder of amino acid transport in the intestine and kidneys. Aminoaciduria that is limited to neutral alpha-amino acids, indicanuria (excludes nutritional pellagra). Oral tryptophan load causes urinary excretion of 5-hydroxyindoleacetic acid. Jejunal and skin biopsies may be required in selected patients. The effects of the disease occur mainly in the brain and skin. Symptoms may begin in infancy or early childhood, but sometimes they begin as late as early adulthood. They can be triggered by sunlight, fever, drugs, emotional, or physical stress. A rash develops on parts of the body exposed to the sun.

Clinical aspects

Routine neonatal urine screening has indicated that many individuals with this defect are asymptomatic. Affected patients develop a photosensitive skin rash, usually beginning in children 3 to 9 years old (but may present during the neonatal period). Typically, after sunlight exposure, the skin reddens. A dry, scaly, well-marginated eruption may develop on the face and other light-exposed areas. With time, pigmentation changes may become definitive. More rarely, episodes of cerebellar ataxia, emotional lability, encephalopathy, and ocular manifestations occur. The episodes are reversible with treatment, which consists of nicotinic acid supplementation with a high-protein diet (in addition to use of creams for protection from sunlight). Exacerbations occur most often in spring or early summer after exposure to sunlight. They may be favored by febrile illness, poor nutrition, treatment with sulfonamides, and emotional stress. Mental retardation, short stature, headaches, unsteady gait, and collapsing or fainting are common. Psychiatric problems (such as anxiety, rapid mood changes, delusions, and hallucinations) may also result.

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