Results: 16% (n=225) presented low values of HVA. Among them we detected patients with different primary deficiencies: tyrosine hydroxylase (n=10), aromatic L-amino acid descaboxylase (n=2), guanosine triphosphate cyclohydrolase 1 (n=4), pyridox(am)ine-5'-phosphate oxidase (n=1) and sepiapterin reductase deficiencies (n=1). As secondary deficiencies, we found hypoxic ischemic encephalopathy and mitochondrial cytopathies, as disorders associated with low HVA values. Regarding high HVA values, this finding was consistently associated with mtDNA deletion syndromes (Kearns-Sayre) Conclusions: Analysis of HVA and others metabolites biomarkers in CSF is useful for the differential diagnosis of primary neurotransmitters diseases. However, concentrations of HVA may be altered by several diseases of the central nervous system as a secondary event. Background: Dopa-responsive dystonia (DRD) is caused by partial defects of guanosine 5'-triphosphate cyclohydrolase I (GTPCH). In this study, we measured neopterin and biopterin level in DRD patients to confirm biochemical diagnosis. Methods: Eleven Japanese patients from 8 families were diagnosed as DRD patients due to heterozygous mutations in GCH1 gene, which codes for GTPCH (DRD (+/−)). Eleven non-dystonic controls were also measured. Their neopterin and biopterin concentrations in plasma and CSF were measured by using HPLC apparatus.