GTP cyclohydrolase I
GTP cyclohydrolase I (GTPCH) (EC 126.96.36.199) is a member of the GTP cyclohydrolase family of enzymes. GTPCH is part of the folate and biopterin biosynthesis pathways. It is responsible for the hydrolysis of guanosine triphosphate (GTP) to form 7,8-dihydroneopterin triphosphate (7,8-DHNP-3'-TP, 7,8-NH2-3'-TP).
GTPCH is encoded by the gene GCH1. Several alternatively spliced transcript variants encoding different isoforms have been described; however, not all of the variants give rise to a functional enzyme.
Mutations in this gene are associated with malignant phenylketonuria (PKU) and hyperphenylalaninemia (HPA), as well as GTP cyclohydrolase I deficiency. Deficiency of GTP cyclohydrolase I can occur in a recessive and in a dominant form and lead to a lack of certain neurotrasmitters (dopamine, norepinephrine, epinephrine and serotonin). The dominant form, with mutation in only one of the two alleles for GTP cyclohydrolase I, causes dopamine-responsive dystonia, characterized by childhood-onset dystonia. Patients with the recessive form have mutations in both alleles for GTP cyclohydrolase I. Patients present with developmental delays and neurological dysfunction with trunk hypotonia, hypertonia of the extremities, abnormal movements, tremors, convulsions, and sometimes autonomic dysfunction. Response to treatment is variable and the long-term and functional outcome is unknown. To provide a basis for improving the understanding of the epidemiology, genotype/phenotype correlation and outcome of these diseases their impact on the quality of life of patients, and for evaluating diagnostic and therapeutic strategies a patient registry was established by the noncommercial International Working Group on Neurotransmitter Related Disorders (iNTD).
The transcribed protein is the first and rate-limiting enzyme in tetrahydrobiopterin (THB, BH4) biosynthesis, catalyzing the conversion of GTP into 7,8-DHNP-3'-TP. THB is an essential cofactor required by the aromatic amino acid hydroxylase (AAAH) and nitric oxide synthase (NOS) enzymes in the biosynthesis of the monoamine neurotransmitters serotonin (5-hydroxytryptamine (5-HT)), melatonin, dopamine, norepinephrine (noradrenaline), and epinephrine (adrenaline), and nitric oxide (NO), respectively.
- GTP+Cyclohydrolase+I at the US National Library of Medicine Medical Subject Headings (MeSH)
- GeneReviews/NCBI/NIH/UW entry on GTP Cyclohydrolase 1-Deficient Dopa-Responsive Dystonia