Hartnup disorder is an inherited metabolic condition that
involves the transport of certain amino acids (for example,
tryptophan and histidine) in the small intestine and kidneys.
Hartnup disorder is possibly the most common metabolic condition
involving amino acids. It is an inherited condition. A child
must inherit a copy of the defective gene from both parents in
order to be seriously affected. The condition usually starts
between ages 3 - 5 years. Most people show no symptoms. If
symptoms do occur, they usually appear in childhood and may
include: - 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
Exams 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. Health care providers can test for
the gene that causes Hartnup disease, SLC6A19.