chr12-4912262-G-A

Variant names:

• chr12-4912262-G-A
• rs778463081
• NM_000217.3:c.884G>A

Variant summary

Our verdict is Likely pathogenic. The variant received 7 ACMG points: 7P and 0B. PM2 PP2 PP3_Strong

The NM_000217.3(KCNA1):​c.884G>A​(p.Arg295His) variant causes a missense change involving the alteration of a conserved nucleotide. The variant was absent in control chromosomes in GnomAD project. In-silico tool predicts a pathogenic outcome for this variant. 14/22 in silico tools predict a damaging outcome for this variant. Variant has been reported in ClinVar as Uncertain significance (★★).

• Frequency: Genomes: not found (cov: 29)
• Consequence: KCNA1 NM_000217.3 missense
• Clinical Significance: Uncertain significance criteria provided, multiple submitters, no conflicts U:4
• Conservation: PhyloP100: 9.93
• Publications: 5 publications found

Genes affected

KCNA1 (HGNC:6218): (potassium voltage-gated channel subfamily A member 1) This gene encodes a voltage-gated delayed potassium channel that is phylogenetically related to the Drosophila Shaker channel. The encoded protein has six putative transmembrane segments (S1-S6), and the loop between S5 and S6 forms the pore and contains the conserved selectivity filter motif (GYGD). The functional channel is a homotetramer. The N-terminus of the channel is associated with beta subunits that can modify the inactivation properties of the channel as well as affect expression levels. The C-terminus of the channel is complexed to a PDZ domain protein that is responsible for channel targeting. Mutations in this gene have been associated with myokymia with periodic ataxia (AEMK). [provided by RefSeq, Jul 2008]

KCNA1 Gene-Disease associations (from GenCC):

• episodic ataxia type 1

  Inheritance: AD Classification: DEFINITIVE, STRONG, SUPPORTIVE Submitted by: Ambry Genetics, ClinGen, Orphanet, Genomics England PanelApp, Labcorp Genetics (formerly Invitae)
• episodic kinesigenic dyskinesia 1

  Inheritance: AD Classification: SUPPORTIVE Submitted by: Orphanet
• isolated autosomal dominant hypomagnesemia, Glaudemans type

  Inheritance: AD Classification: SUPPORTIVE Submitted by: Orphanet
• genetic developmental and epileptic encephalopathy

  Inheritance: AR, AD Classification: SUPPORTIVE, LIMITED Submitted by: G2P, Orphanet

ENSG00000256654 (HGNC:):

ACMG classification

Our verdict: Likely_pathogenic. The variant received 7 ACMG points.

• PM2: Very rare variant in population databases, with high coverage
• PP2: Missense variant in the KCNA1 gene, where missense mutations are typically associated with disease (based on misZ statistic). The gene has 33 curated pathogenic missense variants (we use a threshold of 10). The gene has 3 curated benign missense variants. Gene score misZ: 3.3255 (above the threshold of 3.09). Trascript score misZ: 3.8671 (above the threshold of 3.09). GenCC associations: The gene is linked to isolated autosomal dominant hypomagnesemia, Glaudemans type, episodic ataxia type 1, genetic developmental and epileptic encephalopathy, episodic kinesigenic dyskinesia 1.
• PP3: MetaRNN computational evidence supports a deleterious effect, 0.972

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	MANE	Protein	UniProt
KCNA1	NM_000217.3	c.884G>A	p.Arg295His	missense_variant	Exon 2 of 2	ENST00000382545.5	NP_000208.2

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	TSL	MANE	Protein	Appris	UniProt
KCNA1	ENST00000382545.5	c.884G>A	p.Arg295His	missense_variant	Exon 2 of 2	4	NM_000217.3	ENSP00000371985.3

Frequencies

GnomAD3 genomes Cov.: 29

GnomAD4 exome Cov.: 42

GnomAD4 genome Cov.: 29

ClinVar

Significance: Uncertain significance

Submissions summary: Uncertain:4

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

not provided Uncertain:2

Jul 14, 2024

GeneDx

Significance: Uncertain significance

Review Status: criteria provided, single submitter

Collection Method: clinical testing

Identified heterozygous by whole exome sequencing in an individual with moderate to severe cerebellar atrophy, brisk lower limb reflexes, clonus, slow speech, and learning difficulties (PMID: 33879512); In silico analysis supports that this missense variant has a deleterious effect on protein structure/function; Not observed at significant frequency in large population cohorts (gnomAD); This variant is associated with the following publications: (PMID: 33879512) -

Sep 11, 2017

Athena Diagnostics

Significance: Uncertain significance

Review Status: criteria provided, single submitter

Collection Method: clinical testing

- -

Episodic ataxia type 1 Uncertain:1

Dec 08, 2020

Labcorp Genetics (formerly Invitae), Labcorp

Significance: Uncertain significance

Review Status: criteria provided, single submitter

Collection Method: clinical testing

In summary, the available evidence is currently insufficient to determine the role of this variant in disease. Therefore, it has been classified as a Variant of Uncertain Significance. 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 KCNA1 protein function. This variant has not been reported in the literature in individuals with KCNA1-related conditions. ClinVar contains an entry for this variant (Variation ID: 586092). This variant is not present in population databases (ExAC no frequency). This sequence change replaces arginine with histidine at codon 295 of the KCNA1 protein (p.Arg295His). The arginine residue is highly conserved and there is a small physicochemical difference between arginine and histidine. -

Hereditary ataxia Uncertain:1

Mar 30, 2020

Cambridge Genomics Laboratory, East Genomic Laboratory Hub, NHS Genomic Medicine Service

Significance: Uncertain significance

Review Status: criteria provided, single submitter

Collection Method: clinical testing

- -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Pathogenic	0.99
BayesDel_addAF	Pathogenic	0.56	D
BayesDel_noAF	Pathogenic	0.57
CADD	Pathogenic	34
DANN	Pathogenic	1.0
DEOGEN2	Pathogenic	0.99	D
Eigen	Pathogenic	1.1
Eigen_PC	Pathogenic	1.0
FATHMM_MKL	Pathogenic	0.99	D
LIST_S2	Pathogenic	1.0	D
M_CAP	Pathogenic	0.82	D
MetaRNN	Pathogenic	0.97	D
MetaSVM	Pathogenic	0.98	D
MutationAssessor	Pathogenic	3.9	H
PhyloP100		9.9
PrimateAI	Pathogenic	0.86	D
PROVEAN	Pathogenic	-4.8	D
REVEL	Pathogenic	0.96
Sift	Pathogenic	0.0	D
Sift4G	Pathogenic	0.0010	D
Polyphen		1.0	D
Vest4		0.92
MutPred		0.80		Gain of catalytic residue at R298 (P = 0.0252);
MVP		1.0
MPC		2.6
ClinPred		1.0	D
GERP RS		5.1
PromoterAI		-0.028	Neutral
Varity_R		0.97
gMVP		0.98
Mutation Taster		=25/75	disease causing

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

Other links and lift over

dbSNP: rs778463081; hg19: chr12-5021428; COSMIC: COSV66836531;