Prepair 500+
Gene: GCH1 Green List (high evidence)Comment when marking as ready: Biallelic variants in GCH1 typically result in severe deficiency of GTPCH activity, and result in hyperphenylalaninemia due to secondary PAH deficiency. This can be identified by newborn screening. However, patients with phenotypes that are intermediate between the classic DRD and severe GTPCH deficiency symptoms have been described, such those with severe DRD and additional neurological features but without hyperphenylalaninemia (for review, see Table in Brüggemann et al 2012, PMID 22473768). Because the mechanism of disease in both the monoallelic and biallelic cases is loss of function of GTPCH, and there is a range of GTPCH activity that can cause disease, the decision was made to curate GCH1 for GTPCH deficiency with semi-dominant inheritance. Note that heterozygous parents of biallelic individuals are usually reported as unaffected, although there are some exceptions (Furukawa et al, 1998, PMID 9667588; Bodzioch et al, 2010, PMID 20842687). Reduced penetrance has been reported for individuals with monoallelic GCH1 variants, with penetrance varying according to age and diagnostic criteria. In addition, some variants (e.g. p.Arg184His and p.Lys224Arg) have been reported in monallelic and biallelic individuals. This data was presented to the ClinGen Lumping and Splitting Working Group on November 3, 2020 and there was agreement that GTPCH deficiency should be curated as a semi-dominant trait, including individuals with monoallelic and biallelic GCH1 variants.Created: 21 Nov 2024, 8:54 a.m. | Last Modified: 21 Nov 2024, 8:54 a.m.
Panel Version: 1.592
Green List (high evidence)
Mode of inheritance
BIALLELIC, autosomal or pseudoautosomal
Phenotypes
Dystonia, DOPA-responsive, with or without hyperphenylalaninemia, 128230 (3)
Publications
gene: GCH1 was added gene: GCH1 was added to Prepair 500+. Sources: Mackenzie's Mission,Expert Review Green Mode of inheritance for gene: GCH1 was set to BIALLELIC, autosomal or pseudoautosomal Phenotypes for gene: GCH1 were set to Dystonia, DOPA-responsive, with or without hyperphenylalaninemia, 128230 (3)
If promoting or demoting a gene, please provide comments to justify a decision to move it.
Genes included in a Genomics England gene panel for a rare disease category (green list) should fit the criteria A-E outlined below.
These guidelines were developed as a combination of the ClinGen DEFINITIVE evidence for a causal role of the gene in the disease(a), and the Developmental Disorder Genotype-Phenotype (DDG2P) CONFIRMED DD Gene evidence level(b) (please see the original references provided below for full details). These help provide a guideline for expert reviewers when assessing whether a gene should be on the green or the red list of a panel.
A. There are plausible disease-causing mutations(i) within, affecting or encompassing an interpretable functional region(ii) of this gene identified in multiple (>3) unrelated cases/families with the phenotype(iii).
OR
B. There are plausible disease-causing mutations(i) within, affecting or encompassing cis-regulatory elements convincingly affecting the expression of a single gene identified in multiple (>3) unrelated cases/families with the phenotype(iii).
OR
C. As definitions A or B but in 2 or 3 unrelated cases/families with the phenotype, with the addition of convincing bioinformatic or functional evidence of causation e.g. known inborn error of metabolism with mutation in orthologous gene which is known to have the relevant deficient enzymatic activity in other species; existence of an animal model which recapitulates the human phenotype.
AND
D. Evidence indicates that disease-causing mutations follow a Mendelian pattern of causation appropriate for reporting in a diagnostic setting(iv).
AND
E. No convincing evidence exists or has emerged that contradicts the role of the gene in the specified phenotype.
(i)Plausible disease-causing mutations: Recurrent de novo mutations convincingly affecting gene function. Rare, fully-penetrant mutations - relevant genotype never, or very rarely, seen in controls. (ii) Interpretable functional region: ORF in protein coding genes miRNA stem or loop. (iii) Phenotype: the rare disease category, as described in the eligibility statement. (iv) Intermediate penetrance genes should not be included.
It’s assumed that loss-of-function variants in this gene can cause the disease/phenotype unless an exception to this rule is known. We would like to collect information regarding exceptions. An example exception is the PCSK9 gene, where loss-of-function variants are not relevant for a hypercholesterolemia phenotype as they are associated with increased LDL-cholesterol uptake via LDLR (PMID: 25911073).
If a curated set of known-pathogenic variants is available for this gene-phenotype, please contact us at panelapp@genomicsengland.co.uk
We classify loss-of-function variants as those with the following Sequence Ontology (SO) terms:
Term descriptions can be found on the PanelApp homepage and Ensembl.
If you are submitting this evaluation on behalf of a clinical laboratory please indicate whether you report variants in this gene as part of your current diagnostic practice by checking the box
Standardised terms were used to represent the gene-disease mode of inheritance, and were mapped to commonly used terms from the different sources. Below each of the terms is described, along with the equivalent commonly-used terms.
A variant on one allele of this gene can cause the disease, and imprinting has not been implicated.
A variant on the paternally-inherited allele of this gene can cause the disease, if the alternate allele is imprinted (function muted).
A variant on the maternally-inherited allele of this gene can cause the disease, if the alternate allele is imprinted (function muted).
A variant on one allele of this gene can cause the disease. This is the default used for autosomal dominant mode of inheritance where no knowledge of the imprinting status of the gene required to cause the disease is known. Mapped to the following commonly used terms from different sources: autosomal dominant, dominant, AD, DOMINANT.
A variant on both alleles of this gene is required to cause the disease. Mapped to the following commonly used terms from different sources: autosomal recessive, recessive, AR, RECESSIVE.
The disease can be caused by a variant on one or both alleles of this gene. Mapped to the following commonly used terms from different sources: autosomal recessive or autosomal dominant, recessive or dominant, AR/AD, AD/AR, DOMINANT/RECESSIVE, RECESSIVE/DOMINANT.
A variant on one allele of this gene can cause the disease, however a variant on both alleles of this gene can result in a more severe form of the disease/phenotype.
A variant in this gene can cause the disease in males as they have one X-chromosome allele, whereas a variant on both X-chromosome alleles is required to cause the disease in females. Mapped to the following commonly used term from different sources: X-linked recessive.
A variant in this gene can cause the disease in males as they have one X-chromosome allele. A variant on one allele of this gene may also cause the disease in females, though the disease/phenotype may be less severe and may have a later-onset than is seen in males. X-linked inactivation and mosaicism in different tissues complicate whether a female presents with the disease, and can change over their lifetime. This term is the default setting used for X-linked genes, where it is not known definitately whether females require a variant on each allele of this gene in order to be affected. Mapped to the following commonly used terms from different sources: X-linked dominant, x-linked, X-LINKED, X-linked.
The gene is in the mitochondrial genome and variants within this can cause this disease, maternally inherited. Mapped to the following commonly used term from different sources: Mitochondrial.
Mapped to the following commonly used terms from different sources: Unknown, NA, information not provided.
For example, if the mode of inheritance is digenic, please indicate this in the comments and which other gene is involved.