NM_172107.4:c.1342C>T

Variant names:

• chr20-63415086-G-A
• rs118192226
• NM_172107.4:c.1342C>T

Variant summary

Our verdict is Pathogenic. Variant got 18 ACMG points: 18P and 0B. PVS1 PM2 PP5_Very_Strong

The NM_172107.4(KCNQ2):​c.1342C>T​(p.Arg448*) variant causes a stop gained change. The variant was absent in control chromosomes in GnomAD project. In-silico tool predicts a pathogenic outcome for this variant. Variant has been reported in ClinVar as Pathogenic (★★). Variant results in nonsense mediated mRNA decay.

• Frequency:
  • Genomes: not found (cov: 32)
  • Exomes 𝑓: 0.0 (0 hom.)
  • Failed GnomAD Quality Control
• Consequence: KCNQ2 NM_172107.4 stop_gained
• Clinical Significance: Pathogenic criteria provided, multiple submitters, no conflicts P:7 O:1
• Conservation: PhyloP100: 3.72

Genes affected

KCNQ2 (HGNC:6296): (potassium voltage-gated channel subfamily Q member 2) The M channel is a slowly activating and deactivating potassium channel that plays a critical role in the regulation of neuronal excitability. The M channel is formed by the association of the protein encoded by this gene and a related protein encoded by the KCNQ3 gene, both integral membrane proteins. M channel currents are inhibited by M1 muscarinic acetylcholine receptors and activated by retigabine, a novel anti-convulsant drug. Defects in this gene are a cause of benign familial neonatal convulsions type 1 (BFNC), also known as epilepsy, benign neonatal type 1 (EBN1). At least five transcript variants encoding five different isoforms have been found for this gene. [provided by RefSeq, Jul 2008]

ACMG classification

Verdict is Pathogenic. Variant got 18 ACMG points.

• PVS1: Loss of function variant, product undergoes nonsense mediated mRNA decay. LoF is a known mechanism of disease.
• PM2: Very rare variant in population databases, with high coverage
• PP5: Variant 20-63415086-G-A is Pathogenic according to our data. Variant chr20-63415086-G-A is described in ClinVar as [Pathogenic]. Clinvar id is 21762.Status of the report is criteria_provided_multiple_submitters_no_conflicts, 2 stars. Variant chr20-63415086-G-A is described in Lovd as [Pathogenic]. Variant chr20-63415086-G-A is described in Lovd as [Likely_pathogenic].

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	MANE	Protein	UniProt
KCNQ2	NM_172107.4	c.1342C>T	p.Arg448*	stop_gained	Exon 13 of 17	ENST00000359125.7	NP_742105.1

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	TSL	MANE	Protein	Appris	UniProt
KCNQ2	ENST00000359125.7	c.1342C>T	p.Arg448*	stop_gained	Exon 13 of 17	1	NM_172107.4	ENSP00000352035.2

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD4 exome Data not reliable, filtered out with message: AC0 AF: 0.00 AC: 0 AN: 1451988 Hom.: 0 Cov.: 35 AF XY: 0.00 AC XY: 0 AN XY: 722816

Gnomad4 AFR exome AF: 0.00

Gnomad4 AMR exome AF: 0.00

Gnomad4 ASJ exome AF: 0.00

Gnomad4 EAS exome AF: 0.00

Gnomad4 SAS exome AF: 0.00

Gnomad4 FIN exome AF: 0.00

Gnomad4 NFE exome AF: 0.00

Gnomad4 OTH exome AF: 0.00

GnomAD4 genome Cov.: 32

ClinVar

Significance: Pathogenic

Submissions summary: Pathogenic:7 Other:1

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

not provided Pathogenic:2

May 24, 2016

Eurofins Ntd Llc (ga)

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

- -

Nov 30, 2021

GeneDx

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

Nonsense variant predicted to result in protein truncation or nonsense mediated decay in a gene for which loss-of-function is a known mechanism of disease; Not observed in large population cohorts (Lek et al., 2016); This variant is associated with the following publications: (PMID: 11690625, 25525159, 16686649, 18698150, 14534157, 23360469, 28488083, 32712949, 32770121, 20119593, 30202406) -

Seizures, benign familial neonatal, 1 Pathogenic:1 Other:1

-

GeneReviews

Significance: not provided

Review Status: no classification provided

Collection Method: literature only

BFNIS (benign familial neonatal-infantile seizures) -

Oct 09, 2024

Victorian Clinical Genetics Services, Murdoch Childrens Research Institute

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

Based on the classification scheme VCGS_Germline_v1.3.4, this variant is classified as Pathogenic. Following criteria are met: 0103 - Dominant negative and loss of function are known mechanisms of disease in this gene and are associated with developmental and epileptic encephalopathy 7 (DEE; MIM#613720) and benign neonatal seizures 1 (BFNS1; MIM#121200), respectively (PMID: 20437616). There is currently no phenotypic correlation in terms of variant types or location (PMID: 31418850). (I) 0107 - This gene is associated with autosomal dominant disease. (I) 0112 - The condition associated with this gene has incomplete penetrance; however, this is only reported for individuals with BFNS1 (PMID: 25959266). (I) 0201 - Variant is predicted to cause nonsense-mediated decay (NMD) and loss of protein (premature termination codon is located at least 54 nucleotides upstream of the final exon-exon junction). (SP) 0251 - This variant is heterozygous. (I) 0301 - Variant is absent from gnomAD (both v2 and v3). (SP) 0701 - Other NMD-predicted variants comparable to the one identified in this case have very strong previous evidence for pathogenicity (DECIPHER). (SP) 0801 - This variant has strong previous evidence of pathogenicity in unrelated individuals. This variant has been classified as pathogenic by multiple clinical laboratories in ClinVar and has been observed in families with benign familial neonatal seizures (PMIDs: 20119593, 25982755). (SP) 1203 - This variant has been shown to be de novo in the proband (parental status confirmed) (by trio analysis). (SP) Legend: (SP) - Supporting pathogenic, (I) - Information, (SB) - Supporting benign -

Inborn genetic diseases Pathogenic:1

Nov 23, 2018

Ambry Genetics

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

The p.R448* pathogenic mutation (also known as c.1342C>T), located in coding exon 13 of the KCNQ2 gene, results from a C to T substitution at nucleotide position 1342. This changes the amino acid from an arginine to a stop codon within coding exon 13. This mutation has been reported in multiple families with neonatal and infantile seizures (Singh NA et al. Brain, 2003 Dec;126:2726-37; Yum MS et al. J. Korean Med. Sci., 2010 Feb;25:324-6; Zara F et al. Epilepsia, 2013 Mar;54:425-36; Grinton BE et al. Epilepsia, 2015 Jul;56:1071-80). In addition to the clinical data presented in the literature, this alteration is expected to result in loss of function by premature protein truncation or nonsense-mediated mRNA decay. As such, this alteration is interpreted as a disease-causing mutation. -

Early infantile epileptic encephalopathy with suppression bursts Pathogenic:1

Oct 03, 2024

Labcorp Genetics (formerly Invitae), Labcorp

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

This sequence change creates a premature translational stop signal (p.Arg448*) in the KCNQ2 gene. It is expected to result in an absent or disrupted protein product. Loss-of-function variants in KCNQ2 are known to be pathogenic (PMID: 14534157, 23692823, 27779742). This variant is not present in population databases (gnomAD no frequency). This premature translational stop signal has been observed in individual(s) with benign familial neonatal-infantile seizures (PMID: 3360469, 20119593, 25982755). It has also been observed to segregate with disease in related individuals. ClinVar contains an entry for this variant (Variation ID: 21762). For these reasons, this variant has been classified as Pathogenic. -

Seizure Pathogenic:1

May 25, 2020

Génétique des Maladies du Développement, Hospices Civils de Lyon

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

Truncating variant absent from gnomAD and recurrent in the litterature. -

Developmental and epileptic encephalopathy, 7 Pathogenic:1

-

Lifecell International Pvt. Ltd

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

A Heterozygous Nonsense variant c.1258C>T in Exon 11 of the KCNQ2 gene that results in the amino acid substitution p.Arg420* was identified. The observed variant has a maximum allele frequency of 0.00% in gnomAD exomes and genomes, respectively. The severity of the impact of this variant on the protein is high, based on the effect of the protein and REVEL score. Rare Exome Variant Ensemble Learner (REVEL) is an ensembl method for predicting the pathogenicity of missense variants based on a combination of scores from 13 individual tools: MutPred, FATHMM v2.3, VEST 3.0, PolyPhen-2, SIFT, PROVEAN, MutationAssessor, MutationTaster, LRT, GERP++, SiPhy, phyloP, and phastCons. The REVEL score for an individual missense variant can range from 0 to 1, with higher scores reflecting greater likelihood that the variant is disease-causing. ClinVar has also classified this variant as Pathogenic (Variation ID: 21762). The variant has been previously reported by Grinton BE et al, 2015. Based on the above evidence this variant has been classified as Pathogenic according to the ACMG guidelines. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
BayesDel_addAF	Pathogenic	0.63	D
BayesDel_noAF	Pathogenic	0.63
CADD	Pathogenic	41
DANN	Uncertain	1.0
Eigen	Pathogenic	0.80
Eigen_PC	Pathogenic	0.68
FATHMM_MKL	Uncertain	0.91	D
Vest4		0.96
GERP RS		5.3

Splicing

Name	Calibrated prediction	Score	Prediction
SpliceAI score (max)		0.050		Details are displayed if max score is > 0.2

Find out detailed SpliceAI scores and Pangolin per-transcript scores at spliceailookup.broadinstitute.org

Publications

LitVar

Other links and lift over

dbSNP: rs118192226; hg19: chr20-62046439;