Intellectual disability - microarray and sequencing
Gene: KCNT2 Green List (high evidence)Comment on list classification: New gene submitted by expert reviewer. Based on the evidence provided it was decided that there is enough evidence for this gene to be given Green status.Created: 26 Nov 2019, 2:55 p.m. | Last Modified: 26 Nov 2019, 2:55 p.m.
Panel Version: 2.1116
Comment on mode of pathogenicity: Variants have gain-of-function effect.Created: 26 Nov 2019, 2:46 p.m. | Last Modified: 26 Nov 2019, 2:46 p.m.
Panel Version: 2.1115
Green List (high evidence)
Heterozygous pathogenic KCNT2 variants cause ?Epileptic encephalopathy, early infantile, 57 (MIM 617771).
At least 3 unrelated affected individuals have been reported :
- PMID: 29069600 - Gururaj et al. 2017 : a male child with EOEE (hypotonia, profound DD and intractable infantile seizures) due to a de novo KCNT2 missense variant (NM_001287819.1:c.720T>A or p.Phe240Leu) identified by exome sequencing.
- PMID: 29740868 - Ambrosino et al. 2018 : A girl with phenotype corresponding to West syndrome later evolving to Lennox-Gastaut syndrome. At the age of 9 years the girl displayed severe ID. Trio exome sequencing revealed a de novo missense KCNT2 variant (NM_001287820.2:c.569G>A or p.Arg190His). A 14 y.o. female recruited through the DDD study with phenotype corresponding to epilepsy of infancy with migrating focal seizures. The girl had poor language development and severe learning disability. Infective and metabolic causes were initially ruled out. Trio exome sequencing revealed a de novo missense SNV (c.569G>C or Arg190Pro).
Overall KCNT2 has been commented to contribute to a phenotypic spectrum similar and overlapping to that of KCNT1 (Ambrosino et al.). [KCNT1 is rated green in both epilepsy and ID panels].
KCNT2 was recently included in the epilepsy panel as green (functional studies summarized in the respective reviews). The gene was also recently added to G2P, associated with 'Developmental and infantile epileptic encephalopathy'. It is not commonly included in gene panels for ID offered by diagnostic laboratories.
As a result, KCNT2 could be considered for inclusion in the ID panel with green (or amber) rating.
Sources: LiteratureCreated: 11 Nov 2019, 5:49 p.m.
Mode of inheritance
MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Phenotypes
?Epileptic encephalopathy, early infantile 57, MIM 617771
Publications
Gene: kcnt2 has been classified as Green List (High Evidence).
Mode of pathogenicity for gene: KCNT2 was changed from None to Loss-of-function variants (as defined in pop up message) DO NOT cause this phenotype - please provide details in the comments
Phenotypes for gene: KCNT2 were changed from ?Epileptic encephalopathy, early infantile 57, MIM 617771 to ?Epileptic encephalopathy, early infantile 57, 617771
gene: KCNT2 was added gene: KCNT2 was added to Intellectual disability. Sources: Literature Mode of inheritance for gene: KCNT2 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown Publications for gene: KCNT2 were set to 29069600; 29740868 Phenotypes for gene: KCNT2 were set to ?Epileptic encephalopathy, early infantile 57, MIM 617771 Penetrance for gene: KCNT2 were set to unknown Review for gene: KCNT2 was set to GREEN
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 [email protected]
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.