20-63439610-G-T

Variant names:

• chr20-63439610-G-T
• rs775918190
• NM_172107.4:c.915C>A

Variant summary

Our verdict is Pathogenic. Variant got 15 ACMG points: 15P and 0B. PM1 PM2 PP2 PP3_Moderate PP5_Very_Strong

The NM_172107.4(KCNQ2):​c.915C>A​(p.Phe305Leu) variant causes a missense change involving the alteration of a non-conserved nucleotide. 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 Likely pathogenic (★★).

• Frequency: Genomes: not found (cov: 33)
• Consequence: KCNQ2 NM_172107.4 missense
• Clinical Significance: Pathogenic/Likely pathogenic criteria provided, multiple submitters, no conflicts P:2 O:1
• Conservation: PhyloP100: -2.11

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 15 ACMG points.

• PM1: In a helix (size 41) in uniprot entity KCNQ2_HUMAN there are 12 pathogenic changes around while only 0 benign (100%) in NM_172107.4
• PM2: Very rare variant in population databases, with high coverage
• PP2: Missense variant in the KCNQ2 gene, where missense mutations are typically associated with disease (based on misZ statistic). The gene has 319 curated pathogenic missense variants (we use a threshold of 10). The gene has 78 curated benign missense variants. Gene score misZ: 4.0411 (above the threshold of 3.09). Trascript score misZ: 3.6968 (above the threshold of 3.09). GenCC associations: The gene is linked to seizures, benign familial neonatal, 1, neonatal-onset developmental and epileptic encephalopathy, benign familial neonatal-infantile seizures, benign neonatal seizures, malignant migrating partial seizures of infancy, neonatal encephalopathy with non-epileptic myoclonus, complex neurodevelopmental disorder, seizures, benign familial neonatal, 2, developmental and epileptic encephalopathy, 7, benign familial infantile epilepsy.
• PP3: MetaRNN computational evidence supports a deleterious effect, 0.883
• PP5: Variant 20-63439610-G-T is Pathogenic according to our data. Variant chr20-63439610-G-T is described in ClinVar as [Likely_pathogenic]. Clinvar id is 205887.Status of the report is criteria_provided_multiple_submitters_no_conflicts, 2 stars.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	MANE	Protein	UniProt
KCNQ2	NM_172107.4	c.915C>A	p.Phe305Leu	missense_variant	Exon 6 of 17	ENST00000359125.7	NP_742105.1

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	TSL	MANE	Protein	Appris	UniProt
KCNQ2	ENST00000359125.7	c.915C>A	p.Phe305Leu	missense_variant	Exon 6 of 17	1	NM_172107.4	ENSP00000352035.2

Frequencies

GnomAD3 genomes Cov.: 33

GnomAD4 exome Cov.: 31

GnomAD4 genome Cov.: 33

ClinVar

Significance: Pathogenic/Likely pathogenic

Submissions summary: Pathogenic:2 Other:1

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

Early infantile epileptic encephalopathy with suppression bursts Pathogenic:1

Mar 18, 2019

Labcorp Genetics (formerly Invitae), Labcorp

Significance: Likely pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

A different variant (c.913T>C) giving rise to the same protein effect observed here (p.Phe305Leu) has been determined to be pathogenic (PMID:27779742, 25473036). This suggests that this variant is also likely to be causative of disease. In summary, the currently available evidence indicates that the variant is pathogenic, but additional data are needed to prove that conclusively. Therefore, this variant has been classified as Likely Pathogenic. Algorithms developed to predict the effect of sequence changes on RNA splicing suggest that this variant may create or strengthen a splice site, but this prediction has not been confirmed by published transcriptional studies. This sequence change replaces phenylalanine with leucine at codon 305 of the KCNQ2 protein (p.Phe305Leu). The phenylalanine residue is highly conserved and there is a small physicochemical difference between phenylalanine and leucine. This variant is not present in population databases (ExAC no frequency). This variant has been observed in an individual affected with neonatal epileptic encephalopathy (PMID: 24107868). ClinVar contains an entry for this variant (Variation ID: 205887). Algorithms developed to predict the effect of missense changes on protein structure and function are either unavailable or do not agree on the potential impact of this missense change (SIFT: "Deleterious"; PolyPhen-2: "Possibly Damaging"; Align-GVGD: "Class C15"). -

not provided Pathogenic:1

Feb 05, 2013

GeneDx

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

p.Phe305Leu (TTC>TTA): c.915 C>A in exon 6 of the KCNQ2 gene (NM_172107.2)The Phe305Leu missense change has not been published as a mutation, nor has it been reported as a benign polymorphism to our knowledge. The NHLBI ESP Exome Variant Project has not identified Phe305Leu in approximately 6,500 individuals of European or African American ethnicity, indicating that it is not a common benign variant in these populations. The amino acid substitution is conservative as both Phenylalanine and Leucine are uncharged, non-polar amino acid residues. However, Phe305Leu alters a conserved position in a transmembrane domain in the KCNQ2 protein and other missense mutations in this region of the protein have been identified in patients with benign familial neonatal seizures (Steinlein et al., 2007; Singh et al., 1998). In addition, multiple in-silico algorithms predict it may be damaging to the structure/function of the protein. Therefore, based on the currently available information, Phe305Leu is a strong candidate for a disease-causing mutation, although the possibility that it is a benign variant cannot be excluded. The variant is found in INFANT-EPI panel(s). -

Developmental and epileptic encephalopathy, 7 Other:1

-

GeneReviews

Significance: not provided

Review Status: no classification provided

Collection Method: literature only

EE (epileptic encephalopathy) -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Pathogenic	1.0
BayesDel_addAF	Pathogenic	0.43	D
BayesDel_noAF	Pathogenic	0.38
CADD	Benign	1.5
DANN	Uncertain	0.99
DEOGEN2	Uncertain	0.47	.;.;T;T;D;T;D;T;.;.;.
Eigen	Benign	-0.75
Eigen_PC	Benign	-0.98
FATHMM_MKL	Benign	0.15	N
LIST_S2	Pathogenic	0.98	D;D;D;D;D;D;D;D;D;D;D
M_CAP	Pathogenic	0.79	D
MetaRNN	Pathogenic	0.88	D;D;D;D;D;D;D;D;D;D;D
MetaSVM	Pathogenic	0.82	D
MutationAssessor	Uncertain	2.1	M;.;.;.;.;.;M;.;M;M;M
PrimateAI	Pathogenic	0.89	D
PROVEAN	Pathogenic	-5.5	.;.;.;.;D;.;D;.;D;D;D
REVEL	Pathogenic	0.67
Sift	Uncertain	0.0010	.;.;.;.;D;.;D;.;D;D;D
Sift4G	Uncertain	0.032	D;D;D;D;D;.;D;D;D;D;D
Polyphen		0.99	D;.;.;.;.;.;D;.;D;P;.
Vest4		0.95
MutPred		0.58		Gain of catalytic residue at F305 (P = 0.0621);Gain of catalytic residue at F305 (P = 0.0621);Gain of catalytic residue at F305 (P = 0.0621);Gain of catalytic residue at F305 (P = 0.0621);Gain of catalytic residue at F305 (P = 0.0621);.;Gain of catalytic residue at F305 (P = 0.0621);.;Gain of catalytic residue at F305 (P = 0.0621);Gain of catalytic residue at F305 (P = 0.0621);Gain of catalytic residue at F305 (P = 0.0621);
MVP		0.99
MPC		2.5
ClinPred		1.0	D
GERP RS		-5.4
Varity_R		0.91
gMVP		0.99

Splicing

Name	Calibrated prediction	Score	Prediction
SpliceAI score (max)		0.030		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: rs775918190; hg19: chr20-62070963;