Symptoms:

Most people show no symptoms. If symptoms do occur, they usually appear in childhood and may include:

• Diarrhea
• Mood changes
• Nervous system (neurologic) problems, such as abnormal muscle tone
• Red, scaly skin rash, usually when skin is exposed to sunlight
• Sensitivity to light (photosensitivity)
• Short stature
• Uncoordinated movements

Signs and tests:

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.

The gene for Hartnup has been found, but DNA testing is not yet available. Biochemical tests are available.