12-51662821-G-A

Variant names:

• chr12-51662821-G-A
• rs2138670848
• NM_001330260.2:c.4G>A

Variant summary

Our verdict is Uncertain significance. The variant received 5 ACMG points: 5P and 0B. PM2 PP2 PP3_Moderate

The NM_001330260.2(SCN8A):​c.4G>A​(p.Ala2Thr) 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 Uncertain significance (★).

• Frequency: Genomes: not found (cov: 32)
• Consequence: SCN8A NM_001330260.2 missense
• Clinical Significance: Uncertain significance criteria provided, single submitter U:1
• Conservation: PhyloP100: 10.0
• Publications: 0 publications found

Genes affected

SCN8A (HGNC:10596): (sodium voltage-gated channel alpha subunit 8) This gene encodes a member of the sodium channel alpha subunit gene family. The encoded protein forms the ion pore region of the voltage-gated sodium channel. This protein is essential for the rapid membrane depolarization that occurs during the formation of the action potential in excitable neurons. Mutations in this gene are associated with cognitive disability, pancerebellar atrophy and ataxia. Alternate splicing results in multiple transcript variants.[provided by RefSeq, May 2010]

SCN8A Gene-Disease associations (from GenCC):

• complex neurodevelopmental disorder

  Inheritance: AD Classification: DEFINITIVE Submitted by: ClinGen
• developmental and epileptic encephalopathy, 13

  Inheritance: AD Classification: DEFINITIVE, STRONG Submitted by: Labcorp Genetics (formerly Invitae), G2P, Ambry Genetics
• cognitive impairment with or without cerebellar ataxia

  Inheritance: AD Classification: STRONG Submitted by: Ambry Genetics, Labcorp Genetics (formerly Invitae)
• seizures, benign familial infantile, 5

  Inheritance: AD Classification: STRONG Submitted by: Labcorp Genetics (formerly Invitae)
• benign familial infantile epilepsy

  Inheritance: AD Classification: SUPPORTIVE Submitted by: Orphanet
• infantile convulsions and choreoathetosis

  Inheritance: AD Classification: SUPPORTIVE Submitted by: Orphanet
• undetermined early-onset epileptic encephalopathy

  Inheritance: AD Classification: SUPPORTIVE Submitted by: Orphanet
• myoclonus, familial, 2

  Inheritance: AD Classification: LIMITED Submitted by: Ambry Genetics

ACMG classification

Our verdict: Uncertain_significance. The variant received 5 ACMG points.

• PM2: Very rare variant in population databases, with high coverage
• PP2: Missense variant in the SCN8A gene, where missense mutations are typically associated with disease (based on misZ statistic). The gene has 213 curated pathogenic missense variants (we use a threshold of 10). The gene has 45 curated benign missense variants. Gene score misZ: 0.78755 (below the threshold of 3.09). Trascript score misZ: 10.436 (above the threshold of 3.09). GenCC associations: The gene is linked to myoclonus, familial, 2, developmental and epileptic encephalopathy, 13, undetermined early-onset epileptic encephalopathy, benign familial infantile epilepsy, complex neurodevelopmental disorder, seizures, benign familial infantile, 5, cognitive impairment with or without cerebellar ataxia, infantile convulsions and choreoathetosis.
• PP3: MetaRNN computational evidence supports a deleterious effect, 0.862

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	MANE	Protein	UniProt
SCN8A	NM_001330260.2	c.4G>A	p.Ala2Thr	missense_variant	Exon 2 of 27	ENST00000627620.5	NP_001317189.1
SCN8A	NM_014191.4	c.4G>A	p.Ala2Thr	missense_variant	Exon 2 of 27	ENST00000354534.11	NP_055006.1
SCN8A	NM_001177984.3	c.4G>A	p.Ala2Thr	missense_variant	Exon 2 of 26		NP_001171455.1
SCN8A	NM_001369788.1	c.4G>A	p.Ala2Thr	missense_variant	Exon 2 of 26		NP_001356717.1

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	TSL	MANE	Protein	Appris	UniProt
SCN8A	ENST00000354534.11	c.4G>A	p.Ala2Thr	missense_variant	Exon 2 of 27	1	NM_014191.4	ENSP00000346534.4
SCN8A	ENST00000627620.5	c.4G>A	p.Ala2Thr	missense_variant	Exon 2 of 27	5	NM_001330260.2	ENSP00000487583.2
SCN8A	ENST00000599343.5	c.4G>A	p.Ala2Thr	missense_variant	Exon 1 of 26	5		ENSP00000476447.3
SCN8A	ENST00000355133.7	c.4G>A	p.Ala2Thr	missense_variant	Exon 1 of 25	1		ENSP00000347255.4

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD4 exome Cov.: 31

GnomAD4 genome Cov.: 32

ClinVar

Significance: Uncertain significance

Submissions summary: Uncertain:1

Revision: criteria provided, single submitter

Submissions by phenotype

Developmental and epileptic encephalopathy Uncertain:1

May 28, 2021

Labcorp Genetics (formerly Invitae), Labcorp

Significance: Uncertain significance

Review Status: criteria provided, single submitter

Collection Method: clinical testing

This sequence change replaces alanine with threonine at codon 2 of the SCN8A protein (p.Ala2Thr). The alanine residue is moderately conserved and there is a small physicochemical difference between alanine and threonine. This variant is not present in population databases (ExAC no frequency). This variant has not been reported in the literature in individuals with SCN8A-related conditions. 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: "Tolerated"; PolyPhen-2: "Probably Damaging"; Align-GVGD: "Class C0"). 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. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Uncertain	0.53
BayesDel_addAF	Pathogenic	0.28	D
BayesDel_noAF	Pathogenic	0.17
CADD	Pathogenic	28
DANN	Uncertain	1.0
DEOGEN2	Uncertain	0.46	.;T;.;.;.;.
Eigen	Pathogenic	0.93
Eigen_PC	Pathogenic	0.89
FATHMM_MKL	Pathogenic	0.98	D
LIST_S2	Uncertain	0.94	D;D;D;.;D;D
M_CAP	Pathogenic	0.64	D
MetaRNN	Pathogenic	0.86	D;D;D;D;D;D
MetaSVM	Pathogenic	1.1	D
MutationAssessor	Uncertain	2.4	.;M;M;M;M;M
PhyloP100		10
PrimateAI	Pathogenic	0.79	T
PROVEAN	Benign	-2.0	.;N;N;N;.;.
REVEL	Pathogenic	0.74
Sift	Uncertain	0.0040	.;D;D;D;.;.
Sift4G	Benign	0.26	.;T;T;T;T;T
Polyphen		1.0	.;D;.;.;.;.
Vest4		0.49, 0.47, 0.46, 0.57, 0.49
MutPred		0.30		Gain of phosphorylation at A2 (P = 0.018);Gain of phosphorylation at A2 (P = 0.018);Gain of phosphorylation at A2 (P = 0.018);Gain of phosphorylation at A2 (P = 0.018);Gain of phosphorylation at A2 (P = 0.018);Gain of phosphorylation at A2 (P = 0.018);
MVP		0.90
MPC		2.1
ClinPred		0.95	D
GERP RS		5.0
PromoterAI		-0.13	Neutral
Varity_R		0.23
gMVP		0.64
Mutation Taster		=21/79	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: rs2138670848; hg19: chr12-52056605;