Molecular genetic and metabolic aspects of hph-1,a mouse mutant deficient in gtp cyclohydrolase i activity

GTP cyclohydrolase I (GTP-CH) catalyzes the initial and rate limiting step of the biosynthesis of tetrahydrobiopterin, the cofactor of three aromatic amino acid hydroxylases. Deficiency of this enzyme causes atypical phenylketonuria and hereditary progressive dystonia with marked diurnal fluctuation. To clarify the pathogenesis of the disorder, we analyzed urinary organic acids in adult hph-1, using gas chromatography/mass spectrometry, and found that compared with control mice there were significant increase in phenyl pyruvic acid and decrease in homovanillic acid, although the disappearance of phenylketonuria in hph-1 older than 20 days was previously reported. On the other hand, the structural analysis of the GTP-CH gene from the hph-1 revealed that the sequence of the open reading frame and a part of 5′-flanking region is identical with that of wild type. Further analysis is mandatory to explain the characteristic metabolic abnormality.