20-63408542-G-T

Variant names:

• chr20-63408542-G-T
• rs118192239
• NM_172107.4:c.1764-6C>A

Variant summary

Our verdict is Uncertain significance. Variant got 5 ACMG points: 5P and 0B. PM2 PP3 PP5_Moderate

The NM_172107.4(KCNQ2):​c.1764-6C>A variant causes a splice region, intron change involving the alteration of a non-conserved nucleotide. The variant was absent in control chromosomes in GnomAD project. In-silico tool predicts a benign outcome for this variant. 3/3 splice prediction tools predicting alterations to normal splicing. Variant has been reported in ClinVar as Pathogenic (★).

• Frequency: Genomes: not found (cov: 33)
• Consequence: KCNQ2 NM_172107.4 splice_region, intron
• Scores: Splicing: ADA: 0.9943
• Clinical Significance: Pathogenic criteria provided, single submitter P:1 O:1
• Conservation: PhyloP100: -1.22

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 Uncertain_significance. Variant got 5 ACMG points.

• PM2: Very rare variant in population databases, with high coverage
• PP3: Splicing scoreres supports a deletorius effect: Scorers claiming Pathogenic: dbscSNV1_ADA, dbscSNV1_RF, max_spliceai. No scorers claiming Uncertain. No scorers claiming Benign.
• PP5: Variant 20-63408542-G-T is Pathogenic according to our data. Variant chr20-63408542-G-T is described in ClinVar as [Pathogenic]. Clinvar id is 21815.Status of the report is criteria_provided_single_submitter, 1 stars. Variant chr20-63408542-G-T is described in Lovd as [Pathogenic].

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	MANE	Protein	UniProt
KCNQ2	NM_172107.4	c.1764-6C>A		splice_region_variant, intron_variant	Intron 15 of 16	ENST00000359125.7	NP_742105.1

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	TSL	MANE	Protein	Appris	UniProt
KCNQ2	ENST00000359125.7	c.1764-6C>A		splice_region_variant, intron_variant	Intron 15 of 16	1	NM_172107.4	ENSP00000352035.2

Frequencies

GnomAD3 genomes Cov.: 33

GnomAD4 exome Cov.: 31

GnomAD4 genome Cov.: 33

ClinVar

Significance: Pathogenic

Submissions summary: Pathogenic:1 Other:1

Revision: criteria provided, single submitter

Submissions by phenotype

Early infantile epileptic encephalopathy with suppression bursts Pathogenic:1

Oct 28, 2023

Labcorp Genetics (formerly Invitae), Labcorp

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

This sequence change falls in intron 15 of the KCNQ2 gene. It does not directly change the encoded amino acid sequence of the KCNQ2 protein. This variant is not present in population databases (gnomAD no frequency). This variant has been observed in individual(s) with benign familial neonatal convulsions (PMID: 16686649). It has also been observed to segregate with disease in related individuals. This variant is also known as IVS14-6C>A, Val589X, and p.R588fsX589. ClinVar contains an entry for this variant (Variation ID: 21815). Algorithms developed to predict the effect of variants on protein structure and function are not available or were not evaluated for this variant. Experimental studies have shown that this variant affects KCNQ2 function (PMID: 16686649). Algorithms developed to predict the effect of sequence changes on RNA splicing suggest that this variant may disrupt the consensus splice site. For these reasons, this variant has been classified as Pathogenic. -

Seizures, benign familial neonatal, 1 Other:1

-

GeneReviews

Significance: not provided

Review Status: no classification provided

Collection Method: literature only

BFNE (benign familial neonatal epilepsy). In 1/11 seizures continued until 14 months of age; photosensitive myoclonic epilepsy at age 13 years. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
BayesDel_noAF	Benign	-0.76
CADD	Benign	22
DANN	Benign	0.83

Splicing

Name	Calibrated prediction	Score	Prediction
dbscSNV1_ADA	Pathogenic	0.99
dbscSNV1_RF	Pathogenic	0.86
SpliceAI score (max)		1.0		Details are displayed if max score is > 0.2
DS_AG_spliceai		1.0		Position offset: -2
DS_AL_spliceai		0.38		Position offset: -6

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

Publications

LitVar

Other links and lift over

dbSNP: rs118192239; hg19: chr20-62039895;