20-63406655-GC-G

Variant summary

Our verdict is Likely pathogenic. Variant got 6 ACMG points: 6P and 0B. PM2 PM4 PP5_Moderate

The NM_172107.4(KCNQ2):c.2607del(p.Arg871GlyfsTer59) variant causes a frameshift change involving the alteration of a non-conserved nucleotide. The variant was absent in control chromosomes in GnomAD project. Variant has been reported in ClinVar as Pathogenic (★). Synonymous variant affecting the same amino acid position (i.e. G869G) has been classified as Likely benign.

• Frequency: Genomes: not found (cov: 33)
• Consequence: KCNQ2 NM_172107.4 frameshift
• Clinical Significance: Pathogenic criteria provided, single submitter P:1
• Conservation: PhyloP100: 0.705

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 Likely_pathogenic. Variant got 6 ACMG points.

• PM2: Very rare variant in population databases, with high coverage
• PM4: Frameshift in the end of transcript resulting in stoplost. Downstream stopcodon found after 1122 codons.
• PP5: Variant 20-63406655-GC-G is Pathogenic according to our data. Variant chr20-63406655-GC-G is described in ClinVar as [Pathogenic]. Clinvar id is 2815256.Status of the report is criteria_provided_single_submitter, 1 stars. Variant chr20-63406655-GC-G is described in Lovd as [Pathogenic].

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	UniProt
KCNQ2	NM_172107.4	c.2607del	p.Arg871GlyfsTer59	frameshift_variant	17/17	ENST00000359125.7

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Appris	UniProt
KCNQ2	ENST00000359125.7	c.2607del	p.Arg871GlyfsTer59	frameshift_variant	17/17	1	NM_172107.4	A1

Frequencies

GnomAD3 genomes Cov.: 33

GnomAD4 exome Cov.: 30

GnomAD4 genome Cov.: 33

ClinVar

Significance: Pathogenic

Submissions summary: Pathogenic:1

Revision: criteria provided, single submitter

Submissions by phenotype

Early infantile epileptic encephalopathy with suppression bursts Pathogenic:1

Pathogenic, criteria provided, single submitter

clinical testing

Invitae

Nov 19, 2022

For these reasons, this variant has been classified as Pathogenic. This variant results in an extension of the KCNQ2 protein. Other variant(s) that result in a similarly extended protein product (p.Arg871Glyfs*61) have been determined to be pathogenic (PMID: 14534157, 24375629). This suggests that these extensions are likely to be disease-causing. This variant has not been reported in the literature in individuals affected with KCNQ2-related conditions. This variant is not present in population databases (gnomAD no frequency). This sequence change results in a frameshift in the KCNQ2 gene (p.Arg871Glyfs*59). While this is not anticipated to result in nonsense mediated decay, it is expected to disrupt the last 2 amino acid(s) of the KCNQ2 protein and extend the protein by 56 additional amino acid residues. -

Computational scores

Source: dbNSFP v4.3

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

No publications associated with this variant yet.

Other links and lift over

hg19: chr20-62038008;