rs1057523728

chr20-63439692-A-Gchr20-63439692-A-T

Variant summary

Our verdict is Pathogenic. Variant got 19 ACMG points: 19P and 0B. PM1 PM2 PM5 PP2 PP3_Strong PP5_Very_Strong

The NM_172107.4(KCNQ2):c.833T>C(p.Ile278Thr) variant causes a missense change involving the alteration of a conserved nucleotide. The variant allele was found at a frequency of 0.000000684 in 1,461,148 control chromosomes in the GnomAD database, with no homozygous occurrence. In-silico tool predicts a pathogenic outcome for this variant. Variant has been reported in ClinVar as Likely pathogenic (★★). Another variant affecting the same amino acid position, but resulting in a different missense (i.e. I278F) has been classified as Likely pathogenic.

• Frequency:
  • Genomes: not found (cov: 33)
  • Exomes 𝑓: 6.8e-7 (0 hom.)
• Consequence: KCNQ2 NM_172107.4 missense
• Clinical Significance: Pathogenic/Likely pathogenic criteria provided, multiple submitters, no conflicts P:5 O:1
• Conservation: PhyloP100: 9.01

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 19 ACMG points.

• PM1: In a hotspot region, there are 15 aminoacids with missense pathogenic changes in the window of +-8 aminoacids around while only 0 benign, 6 uncertain in NM_172107.4
• PM2: Very rare variant in population databases, with high coverage
• PM5: Other missense variant is known to change same aminoacid residue: Variant chr20-63439693-T-A is described in ClinVar as [Likely_pathogenic]. Clinvar id is 1349168.Status of the report is criteria_provided_single_submitter, 1 stars.
• PP2: Missense variant where missense usually causes diseases, KCNQ2
• PP3: MetaRNN computational evidence supports a deleterious effect, 0.957
• PP5: Variant 20-63439692-A-G is Pathogenic according to our data. Variant chr20-63439692-A-G is described in ClinVar as [Likely_pathogenic]. Clinvar id is 429212.Status of the report is criteria_provided_multiple_submitters_no_conflicts, 2 stars.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	UniProt
KCNQ2	NM_172107.4	c.833T>C	p.Ile278Thr	missense_variant	6/17	ENST00000359125.7

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Appris	UniProt
KCNQ2	ENST00000359125.7	c.833T>C	p.Ile278Thr	missense_variant	6/17	1	NM_172107.4	A1

Frequencies

GnomAD3 genomes Cov.: 33

GnomAD4 exome AF: 6.84e-7 AC: 1 AN: 1461148 Hom.: 0 Cov.: 31 AF XY: 0.00 AC XY: 0 AN XY: 726930

Gnomad4 AFR exome AF: 0.0000299

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.: 33

ClinVar

Significance: Pathogenic/Likely pathogenic

Submissions summary: Pathogenic:5 Other:1

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

KCNQ2-related disorder Pathogenic:2

Pathogenic, criteria provided, single submitter	clinical testing	PreventionGenetics, part of Exact Sciences	Oct 25, 2023	The KCNQ2 c.833T>C variant is predicted to result in the amino acid substitution p.Ile278Thr. This variant was reported in several individuals with early infantile epileptic encephalopathy and at least in two cases was determined to occur de novo (Table 2, Ostrander et al. 2018. PubMed ID: 30109124; Table 1A, Fernández-Marmiesse et al. 2019. PubMed ID: 31780880; Table S5, Barbosa-Gouveia et al. 2021. PubMed ID: 34440436). Functional studies show that this variant affects protein function (Figure 5, Vanoye et al. 2022. PubMed ID: 35104249). An different variant affecting the same codon (p.Ile278Phe) was observed de novo in an individual with epilepsy (Table 1, Gong et al. 2021. PubMed ID: 33897753). This variant has not been reported in a large population database (http://gnomad.broadinstitute.org), indicating this variant is rare. This variant is interpreted as pathogenic. -
Likely pathogenic, criteria provided, single submitter	clinical testing	Kasturba Medical College, Manipal, Kasturba Medical College, Manipal, Manipal Academy of Higher Education, Manipal, India	-	- -

Early infantile epileptic encephalopathy with suppression bursts Pathogenic:1

Pathogenic, criteria provided, single submitter

clinical testing

Invitae

Mar 23, 2023

This variant is not present in population databases (gnomAD no frequency). For these reasons, this variant has been classified as Pathogenic. This variant disrupts the p.Ile278 amino acid residue in KCNQ2. Other variant(s) that disrupt this residue have been determined to be pathogenic (Invitae). This suggests that this residue is clinically significant, and that variants that disrupt this residue are likely to be disease-causing. Advanced modeling of protein sequence and biophysical properties (such as structural, functional, and spatial information, amino acid conservation, physicochemical variation, residue mobility, and thermodynamic stability) performed at Invitae indicates that this missense variant is expected to disrupt KCNQ2 protein function. ClinVar contains an entry for this variant (Variation ID: 429212). This missense change has been observed in individual(s) with clinical features of KCNQ2-related conditions (PMID: 30109124). In at least one individual the variant was observed to be de novo. This sequence change replaces isoleucine, which is neutral and non-polar, with threonine, which is neutral and polar, at codon 278 of the KCNQ2 protein (p.Ile278Thr). -

not provided Pathogenic:1

Pathogenic, criteria provided, single submitter

clinical testing

GeneDx

Dec 02, 2021

Not observed in large population cohorts (Lek et al., 2016); Missense variants in this gene are often considered pathogenic (Stenson et al., 2014); In silico analysis supports that this missense variant has a deleterious effect on protein structure/function; This variant is associated with the following publications: (PMID: 30109124, 31780880, 27602407) -

Developmental and epileptic encephalopathy, 7 Pathogenic:1

Likely pathogenic, criteria provided, single submitter

clinical testing

NeuroMeGen, Hospital Clinico Santiago de Compostela

Jan 01, 2018

- -

Complex neurodevelopmental disorder Other:1

not provided, no classification provided

literature only

Channelopathy-Associated Epilepsy Research Center

-

- -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Pathogenic	0.98
BayesDel_addAF	Pathogenic	0.55	D
BayesDel_noAF	Pathogenic	0.55
Cadd	Pathogenic	28
Dann	Uncertain	1.0
Eigen	Uncertain	0.60
Eigen_PC	Uncertain	0.54
FATHMM_MKL	Pathogenic	0.98	D
LIST_S2	Pathogenic	0.99	D;D;D;D;D;D;D;D;D;D;D
M_CAP	Pathogenic	0.94	D
MetaRNN	Pathogenic	0.96	D;D;D;D;D;D;D;D;D;D;D
MetaSVM	Pathogenic	1.1	D
MutationAssessor	Uncertain	2.1	M;.;.;.;.;.;M;.;M;M;M
MutationTaster	Benign	1.0	D;D;D;D;D;D;D;D;D;D;D;D
PrimateAI	Pathogenic	0.88	D
Sift4G	Uncertain	0.0020	D;D;D;D;D;.;D;D;D;D;D
Polyphen		1.0	D;.;.;.;.;.;D;.;D;D;.
Vest4		0.95
MutPred		0.77		Loss of stability (P = 0.0072);Loss of stability (P = 0.0072);Loss of stability (P = 0.0072);Loss of stability (P = 0.0072);Loss of stability (P = 0.0072);.;Loss of stability (P = 0.0072);.;Loss of stability (P = 0.0072);Loss of stability (P = 0.0072);Loss of stability (P = 0.0072);
MVP		1.0
MPC		3.1
ClinPred		1.0	D
GERP RS		4.0
Varity_R		0.93
gMVP		1.0

Splicing

Name	Calibrated prediction	Score	Prediction
SpliceAI score (max)		0.0		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: rs1057523728; hg19: chr20-62071045;