12-4912055-C-G

Variant names:

• chr12-4912055-C-G
• rs28933383
• NM_000217.3:c.677C>G

Variant summary

Our verdict is Pathogenic. The variant received 23 ACMG points: 23P and 0B. PS3 PM1 PM2 PM5 PP2 PP3_Strong PP5_Very_Strong

The NM_000217.3(KCNA1):​c.677C>G​(p.Thr226Arg) 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. Variant has been reported in ClinVar as Pathogenic (★★). ClinVar reports functional evidence for this variant: "SCV001984848: Functional studies suggest the p.Thr226Arg exerts a dominant negative effect on potassium channel function and may impair neuronal repolarization (PMID:10355668, 10414318, 11773313). An in-vitro study of this variant in rat neurons detected no effect on neuronal excitability" and additional evidence is available in ClinVar. Another variant affecting the same amino acid position, but resulting in a different missense (i.e. T226M) has been classified as Pathogenic.

• Frequency: Genomes: not found (cov: 31)
• Consequence: KCNA1 NM_000217.3 missense
• Clinical Significance: Pathogenic criteria provided, multiple submitters, no conflicts P:4 O:1
• Conservation: PhyloP100: 7.85
• Publications: 37 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: Labcorp Genetics (formerly Invitae), Ambry Genetics, ClinGen, Genomics England PanelApp, Orphanet
• episodic kinesigenic dyskinesia 1

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

  Inheritance: AD, AR Classification: SUPPORTIVE, LIMITED Submitted by: Orphanet, G2P
• isolated autosomal dominant hypomagnesemia, Glaudemans type

  Inheritance: AD Classification: SUPPORTIVE Submitted by: Orphanet

ENSG00000256654 (HGNC:):

ACMG classification

Our verdict: Pathogenic. The variant received 23 ACMG points.

• PS3: PS3 evidence extracted from ClinVar submissions: SCV001984848: Functional studies suggest the p.Thr226Arg exerts a dominant negative effect on potassium channel function and may impair neuronal repolarization (PMID: 10355668, 10414318, 11773313). An in-vitro study of this variant in rat neurons detected no effect on neuronal excitability; however, it identified increased neurotransmitter release (PMID: 19779067).; SCV002028123: Functional studies indicated that T226R results in a decrease in voltage activated current and cause a dominant negative effect on potassium channel function (PMID: 10355668, 10414318)
• PM1: In a transmembrane_region Helical; Name=Segment S2 (size 21) in uniprot entity KCNA1_HUMAN there are 6 pathogenic changes around while only 0 benign (100%) in NM_000217.3
• PM2: Very rare variant in population databases, with high coverage
• PM5: Other missense variant is known to change same aminoacid residue: Variant chr12-4912055-C-T is described in ClinVar as Pathogenic. ClinVar VariationId is 21127.Status of the report is criteria_provided_multiple_submitters_no_conflicts, 2 stars.
• 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 episodic ataxia type 1, genetic developmental and epileptic encephalopathy, isolated autosomal dominant hypomagnesemia, Glaudemans type, episodic kinesigenic dyskinesia 1.
• PP3: MetaRNN computational evidence supports a deleterious effect, 0.976
• PP5: Variant 12-4912055-C-G is Pathogenic according to our data. Variant chr12-4912055-C-G is described in ClinVar as Pathogenic. ClinVar VariationId is 13492.Status of the report is criteria_provided_multiple_submitters_no_conflicts, 2 stars.

Variant Effect in Transcripts

ACMG analysis was done for transcript: NM_000217.3. You can select a different transcript below to see updated ACMG assignments.

RefSeq Transcripts

Sel.	Gene	Transcript	Tags	HGVSc	HGVSp	Effect	Exon Rank	Protein	UniProt
	KCNA1	NM_000217.3	MANE Select	c.677C>G	p.Thr226Arg	missense	Exon 2 of 2	NP_000208.2	Q09470

Ensembl Transcripts

Sel.	Gene	Transcript	Tags	HGVSc	HGVSp	Effect	Exon Rank	Protein	UniProt
	KCNA1	ENST00000382545.5	TSL:4 MANE Select	c.677C>G	p.Thr226Arg	missense	Exon 2 of 2	ENSP00000371985.3	Q09470
	KCNA1	ENST00000639306.1	TSL:5	n.515C>G		non_coding_transcript_exon	Exon 1 of 2	ENSP00000492506.1	A0A1W2PRI2
	ENSG00000256654	ENST00000541095.1	TSL:3	n.105+1583C>G		intron	N/A

Frequencies

GnomAD3 genomes Cov.: 31

GnomAD4 exome Cov.: 35

GnomAD4 genome Cov.: 31

ClinVar

ClinVar submissions

Significance: Pathogenic

Revision: criteria provided, multiple submitters, no conflicts

Pathogenic	VUS	Benign	Condition
2	-	-	Episodic ataxia type 1 (3)
2	-	-	not provided (2)

Computational scores

Source: dbNSFP v4.9

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Pathogenic	1.0
BayesDel_addAF	Pathogenic	0.55	D
BayesDel_noAF	Pathogenic	0.55
CADD	Pathogenic	28
DANN	Uncertain	1.0
DEOGEN2	Pathogenic	0.96	D
Eigen	Pathogenic	0.90
Eigen_PC	Pathogenic	0.81
FATHMM_MKL	Pathogenic	0.99	D
LIST_S2	Uncertain	0.96	D
M_CAP	Pathogenic	0.56	D
MetaRNN	Pathogenic	0.98	D
MetaSVM	Pathogenic	1.1	D
MutationAssessor	Uncertain	2.9	M
PhyloP100		7.9
PrimateAI	Pathogenic	0.86	D
PROVEAN	Pathogenic	-5.7	D
REVEL	Pathogenic	0.96
Sift	Pathogenic	0.0	D
Sift4G	Uncertain	0.0050	D
Polyphen		1.0	D
Vest4		0.89
MutPred		0.81		Gain of catalytic residue at F221 (P = 2e-04)
MVP		0.99
MPC		2.5
ClinPred		1.0	D
GERP RS		4.9
PromoterAI		-0.0094	Neutral
Varity_R		0.96
gMVP		0.98
Mutation Taster		=6/94	disease causing (ClinVar)

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: rs28933383; hg19: chr12-5021221;