Urinary Neopterin and Phenylalanine Loading Test as Tools for the Biochemical Diagnosis of Segawa Disease

Background. The diagnosis of autosomaldominant GTP-cyclohydrolasedeficiency relies on the examination of the GCH1 gene and/or pterinsand neurotransmittersin CSF. The aim of the study was to assess the diagnostic value, if any, of pterinsin urine and blood phenylalanine(Phe) and tyrosine (Tyr) under oral Phe loading test.