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GCH1
GTP cyclohydrolase 1
The GCH1 gene provides instructions for producing GTP cyclohydrolase 1, an enzyme essential for synthesising tetrahydrobiopterin (BH4), a co-factor vital for neurotransmitter production. GCH1 plays a crucial role in maintaining proper neurological function by regulating the synthesis of key neurotransmitters.
GCH1 is located on the long (q) arm of chromosome 14, at band 14q22.2. Arm ratio per GRCh38 - banding schematic.
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Overview
The GCH1 gene encodes for the enzyme GTP cyclohydrolase 1, which is involved in a critical biochemical pathway. This enzyme is responsible for the initial step in the production of tetrahydrobiopterin (BH4) [PMID:35733596]. BH4 acts as a co-factor for several enzymes, including those that process amino acids and synthesise neurotransmitters [PMID:35733596].
Disruptions in GCH1 function can lead to conditions primarily affecting the nervous system, such as dopa-responsive dystonia. These conditions often manifest with movement disorders and can be inherited in either an autosomal dominant or autosomal recessive manner.
What the gene does
The GCH1 gene directs the synthesis of GTP cyclohydrolase 1, an enzyme that initiates the production of tetrahydrobiopterin (BH4) [PMID:35733596]. BH4 is a vital co-factor involved in various metabolic processes within the body. One of its key roles is collaborating with the enzyme phenylalanine hydroxylase to convert the amino acid phenylalanine into tyrosine.
Furthermore, BH4 is indispensable for the synthesis of neurotransmitters, which are chemical messengers facilitating communication between nerve cells in the brain [PMID:35733596]. Specifically, it is involved in producing dopamine, which is crucial for regulating smooth physical movements, and serotonin, which influences mood, emotion, sleep, and appetite. Thus, the enzyme encoded by GCH1 is fundamental for normal neurological function and overall metabolic balance.
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Chromosome location
The GCH1 gene is located on chromosome 14 at position 14q22.2. This specific genomic location positions the gene within a region that can impact various cellular processes. The gene's presence on chromosome 14 means it is found in both copies of chromosome 14 within an individual's cells.
Protein structure
The GTP cyclohydrolase 1 protein consists of 250 amino acids. Its structural composition includes a Disordered region, which spans amino acids 1 to 64. Disordered regions are characterised by their lack of a fixed three-dimensional structure under physiological conditions, often playing roles in molecular recognition, signalling, and regulation due to their flexibility.
Key variants
Variants within the GCH1 gene can alter the function of the GTP cyclohydrolase 1 enzyme, potentially leading to a reduction in tetrahydrobiopterin (BH4) production. These genetic changes can range from single nucleotide substitutions to larger deletions or insertions. The impact of a variant depends on its specific location and the resulting alteration to the protein's structure or function.
Sample of pathogenic variants
10 pathogenic / likely-pathogenic variants from ClinVar, ranked by review status (expert-panel-reviewed first). This is a sample; recurrent founder variants in a specific population may not appear here - see the full ClinVar listing via the link above.
| Variant (HGVS) | Protein change | Classification | Evidence | Associated condition |
|---|---|---|---|---|
c.248dup | p.Glu84fs | Pathogenic/Likely pathogenic | ★★☆☆ | Dystonia 5 |
c.250G>T | p.Glu84Ter | Pathogenic | ★★☆☆ | GTP cyclohydrolase I deficiency |
c.478A>T | p.Lys160Ter | Pathogenic/Likely pathogenic | ★★☆☆ | Dystonia 5 |
c.539A>G | p.Gln180Arg | Pathogenic/Likely pathogenic | ★★☆☆ | Dystonia 5 |
c.541+2T>C | - | Pathogenic | ★★☆☆ | GTP cyclohydrolase I deficiency |
c.550C>T | p.Arg184Cys | Pathogenic/Likely pathogenic | ★★☆☆ | Dystonia 5 |
c.578_583del | p.Ile193_Glu195delinsLys | Pathogenic/Likely pathogenic | ★★☆☆ | GTP cyclohydrolase I deficiency |
c.597del | p.Ala200fs | Pathogenic/Likely pathogenic | ★★☆☆ | GTP cyclohydrolase I deficiency |
c.614T>A | p.Val205Glu | Pathogenic | ★★☆☆ | Dystonia 5 |
c.626+2dup | - | Pathogenic/Likely pathogenic | ★★☆☆ | Dystonia 5 |
Evidence stars indicate ClinVar review status. Individual variant interpretation should always be performed by a qualified clinical laboratory - many variants remain classified as Variants of Uncertain Significance (VUS) pending more research.
Associated conditions
Variants in the GCH1 gene are associated with a spectrum of conditions, including GTP cyclohydrolase deficiency (Segawa disease). This condition, also known as Dopa-responsive dystonia, is primarily characterised by involuntary muscle contractions and movement difficulties. Another associated condition is tetrahydrobiopterin deficiency, which can result from GCH1 gene variants and accounts for a small percentage of all cases of this broader deficiency.
Inheritance pattern
Conditions caused by pathogenic GCH1 variants typically follow ad/ar inheritance.
Each child has a 50% chance of inheriting the pathogenic variant, regardless of sex.
UK clinical status
The GCH1 gene is recognised within the NHS Genomic Medicine Service, with its clinical relevance noted across several PanelApp panels. These include 'DDG2P', 'Dystonia, chorea or related movement disorder, adult onset', 'Dystonia, chorea or related movement disorder, childhood onset', 'Early onset dystonia', 'Hereditary spastic paraplegia, adult onset', 'Hereditary spastic paraplegia, childhood onset', 'Intellectual disability', 'Likely inborn error of metabolism', 'Neurodegenerative disorders, adult onset', 'Neurotransmitter disorders', 'Parkinson Disease and Complex Parkinsonism', and 'Undiagnosed metabolic disorders'. Its 'green' status on these panels indicates that there is strong evidence for a gene-disease association.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
What is the primary function of the GCH1 gene?
The GCH1 gene provides instructions for creating the enzyme GTP cyclohydrolase 1, which is crucial for the initial step in producing tetrahydrobiopterin (BH4). BH4 acts as a co-factor for various enzymes, notably those involved in processing amino acids and synthesising neurotransmitters like dopamine and serotonin.
What health conditions are associated with GCH1 gene variants?
Variants in the GCH1 gene are primarily associated with GTP cyclohydrolase deficiency, also known as dopa-responsive dystonia. This condition causes involuntary muscle movements. Additionally, GCH1 variants can lead to a specific form of tetrahydrobiopterin deficiency.
How are GCH1-related conditions typically inherited?
Conditions linked to the GCH1 gene can be inherited in either an autosomal dominant or autosomal recessive pattern. This means that depending on the specific variant and condition, either one altered copy or two altered copies of the gene may be necessary for the condition to manifest.
References
- Longo N. Disorders of biopterin metabolism. Journal of inherited metabolic disease. 2009. PMID: 19234759
- Segawa M. Autosomal dominant GTP cyclohydrolase I (AD GCH 1) deficiency (Segawa disease, dystonia 5; DYT 5). Chang Gung medical journal. 2009. PMID: 19292934
- Trender-Gerhard I, Sweeney MG, Schwingenschuh P. Autosomal-dominant GTPCH1-deficient DRD: clinical characteristics and long-term outcome of 34 patients. Journal of neurology, neurosurgery, and psychiatry. 2009. PMID: 19332422
- Clot F, Grabli D, Cazeneuve C. Exhaustive analysis of BH4 and dopamine biosynthesis genes in patients with Dopa-responsive dystonia. Brain : a journal of neurology. 2009. PMID: 19491146
- Ohta E, Funayama M, Ichinose H. Novel mutations in the guanosine triphosphate cyclohydrolase 1 gene associated with DYT5 dystonia. Archives of neurology. 2006. PMID: 17101830
- Garavaglia B, Invernizzi F, Carbone ML. GTP-cyclohydrolase I gene mutations in patients with autosomal dominant and recessive GTP-CH1 deficiency: identification and functional characterization of four novel mutations. Journal of inherited metabolic disease. 2004. PMID: 15303002
- Müller U, Steinberger D, Topka H. Mutations of GCH1 in Dopa-responsive dystonia. Journal of neural transmission (Vienna, Austria : 1996). 2002. PMID: 11956954
- Shintaku H. Disorders of tetrahydrobiopterin metabolism and their treatment. Current drug metabolism. 2002. PMID: 12003346
- Blau N, Bonafé L, Thöny B. Tetrahydrobiopterin deficiencies without hyperphenylalaninemia: diagnosis and genetics of dopa-responsive dystonia and sepiapterin reductase deficiency. Molecular genetics and metabolism. 2001. PMID: 11592814
- Thöny B, Auerbach G, Blau N. Tetrahydrobiopterin biosynthesis, regeneration and functions. The Biochemical journal. 2000. PMID: 10727395