Neurologic manifestations include cerebellar ataxia and psychologic abnormalities. Mental retardation, short stature, headache, and collapsing or fainting are common. Symptoms may be precipitated by sunlight, fever, drugs, or other stresses. Poor nutritional intake nearly always precedes appearance of symptoms. The eventual prognosis is good, and the frequency of attacks usually diminishes with age.
Diagnosis is made by demonstrating the characteristic amino acid excretion pattern in the urine.
Indoles and other tryptophan degradation products in the urine provide supplementary evidence of the disease.