rs1555226375

Positions:

• chr12-51770601-G-A

Variant summary

Our verdict is Likely pathogenic. Variant got 8 ACMG points: 8P and 0B. PM2 PP2 PP3_Strong PP5

The NM_014191.4(SCN8A):​c.3563G>A​(p.Arg1188Gln) variant causes a missense change involving the alteration of a conserved nucleotide. The variant allele was found at a frequency of 0.00000137 in 1,461,778 control chromosomes in the GnomAD database, with no homozygous occurrence. In-silico tool predicts a pathogenic outcome for this variant. Variant has been reported in ClinVar as Conflicting classifications of pathogenicity (no stars).

• Frequency:
  • Genomes: not found (cov: 32)
  • Exomes 𝑓: 0.0000014 (0 hom.)
• Consequence: SCN8A NM_014191.4 missense
• Clinical Significance: Conflicting classifications of pathogenicity criteria provided, conflicting classifications P:4 U:1
• Conservation: PhyloP100: 10.0

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]

ACMG classification

Verdict is Likely_pathogenic. Variant got 8 ACMG points.

• PM2: Very rare variant in population databases, with high coverage
• PP2: Missense variant in gene, where missense usually causes diseases (based on misZ statistic), SCN8A. . Gene score misZ 0.78755 (greater than the threshold 3.09). Trascript score misZ 10.278 (greater than threshold 3.09). GenCC has associacion of gene with myoclonus, familial, 2, infantile convulsions and choreoathetosis, cognitive impairment with or without cerebellar ataxia, undetermined early-onset epileptic encephalopathy, complex neurodevelopmental disorder, developmental and epileptic encephalopathy, 13, benign familial infantile epilepsy, seizures, benign familial infantile, 5.
• PP3: MetaRNN computational evidence supports a deleterious effect, 0.989
• PP5: Variant 12-51770601-G-A is Pathogenic according to our data. Variant chr12-51770601-G-A is described in ClinVar as [Conflicting_classifications_of_pathogenicity]. Clinvar id is 461339.We mark this variant Likely_pathogenic, oryginal submissions are: {Likely_pathogenic=2, Uncertain_significance=1, Pathogenic=1}.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
SCN8A	NM_001330260.2	c.3563G>A	p.Arg1188Gln	missense_variant	19/27	ENST00000627620.5	NP_001317189.1
SCN8A	NM_014191.4	c.3563G>A	p.Arg1188Gln	missense_variant	19/27	ENST00000354534.11	NP_055006.1
SCN8A	NM_001177984.3	c.3563G>A	p.Arg1188Gln	missense_variant	19/26		NP_001171455.1
SCN8A	NM_001369788.1	c.3563G>A	p.Arg1188Gln	missense_variant	19/26		NP_001356717.1

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
SCN8A	ENST00000354534.11	c.3563G>A	p.Arg1188Gln	missense_variant	19/27	1	NM_014191.4	ENSP00000346534	P4
SCN8A	ENST00000627620.5	c.3563G>A	p.Arg1188Gln	missense_variant	19/27	5	NM_001330260.2	ENSP00000487583	A1

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD4 exome AF: 0.00000137 AC: 2 AN: 1461778 Hom.: 0 Cov.: 31 AF XY: 0.00 AC XY: 0 AN XY: 727174

Gnomad4 AFR exome AF: 0.00

Gnomad4 AMR exome AF: 0.00

Gnomad4 ASJ exome AF: 0.00

Gnomad4 EAS exome AF: 0.00

Gnomad4 SAS exome AF: 0.00

Gnomad4 FIN exome AF: 0.00

Gnomad4 NFE exome AF: 0.00000180

Gnomad4 OTH exome AF: 0.00

GnomAD4 genome Cov.: 32

EpiCase AF: 0.0000545

EpiControl AF: 0.00

ClinVar

Significance: Conflicting classifications of pathogenicity

Submissions summary: Pathogenic:4 Uncertain:1

Revision: criteria provided, conflicting classifications

Submissions by phenotype

Cognitive impairment with or without cerebellar ataxia Pathogenic:1

Likely pathogenic, no assertion criteria provided

provider interpretation

Solve-RD Consortium

Jun 01, 2022

Variant confirmed as disease-causing by referring clinical team -

Early infantile epileptic encephalopathy with suppression bursts Pathogenic:1

Pathogenic, criteria provided, single submitter

clinical testing

Labcorp Genetics (formerly Invitae), Labcorp

Nov 27, 2023

This sequence change replaces arginine, which is basic and polar, with glutamine, which is neutral and polar, at codon 1188 of the SCN8A protein (p.Arg1188Gln). This variant is not present in population databases (gnomAD no frequency). This missense change has been observed in individual(s) with clinical features of SCN8A-related conditions (Invitae). In at least one individual the variant was observed to be de novo. ClinVar contains an entry for this variant (Variation ID: 461339). 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 SCN8A protein function with a positive predictive value of 95%. For these reasons, this variant has been classified as Pathogenic. -

not provided Pathogenic:1

Likely pathogenic, criteria provided, single submitter

clinical testing

GeneDx

Aug 14, 2023

Not observed at significant frequency in large population cohorts (gnomAD); In silico analysis supports that this missense variant has a deleterious effect on protein structure/function; Missense variants in this gene are often considered pathogenic (HGMD); This substitution is predicted to be in the cytoplasmic loop between the second and third homologous domains; Has not been previously published as pathogenic or benign to our knowledge -

Developmental and epileptic encephalopathy, 13 Pathogenic:1

Likely pathogenic, criteria provided, single submitter

clinical testing

Neuberg Centre For Genomic Medicine, NCGM

Mar 01, 2023

The missense variant c.3563G>A (p.Arg1188Gln) in the SCN8A gene has not been reported previously as a pathogenic variant nor as a benign variant, to our knowledge. In in-vitro studies, algorithms were developed to predict the effect of sequence changes on RNA splicing suggesting that this variant may create or strengthen a splice site. This variant is novel (not in any individuals) in gnomAD Exomes and 1000 Genomes. It has been submitted to ClinVar as Likely Pathogenic/Uncertain significance. The amino acid Arginine at position 1188 is changed to a Glutamine changing protein sequence and it might alter its composition and physico-chemical properties. The variant is predicted as damaging by SIFT. The amino acid change p.Arg1188Gln in SCN8A is predicted as conserved by GERP++ and PhyloP across 100 vertebrates. For these reasons, this variant has been classified as Likely Pathogenic -

Inborn genetic diseases Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Ambry Genetics

Nov 21, 2018

The p.R1188Q variant (also known as c.3563G>A), located in coding exon 18 of the SCN8A gene, results from a G to A substitution at nucleotide position 3563. The arginine at codon 1188 is replaced by glutamine, an amino acid with highly similar properties. This amino acid position is highly conserved in available vertebrate species. In addition, this alteration is predicted to be deleterious by in silico analysis. Since supporting evidence is limited at this time, the clinical significance of this alteration remains unclear. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Pathogenic	0.95
BayesDel_addAF	Pathogenic	0.58	D
BayesDel_noAF	Pathogenic	0.60
CADD	Pathogenic	32
DANN	Pathogenic	1.0
DEOGEN2	Pathogenic	0.87	D;.;.;.;.
Eigen	Pathogenic	1.1
Eigen_PC	Pathogenic	1.0
FATHMM_MKL	Pathogenic	0.99	D
LIST_S2	Pathogenic	0.99	D;D;.;D;D
M_CAP	Pathogenic	0.79	D
MetaRNN	Pathogenic	0.99	D;D;D;D;D
MetaSVM	Pathogenic	1.1	D
MutationAssessor	Pathogenic	4.4	H;H;H;.;H
MutationTaster	Benign	1.0	D;D
PrimateAI	Uncertain	0.78	T
PROVEAN	Uncertain	-3.8	D;D;D;.;.
REVEL	Pathogenic	0.96
Sift	Pathogenic	0.0	D;D;D;.;.
Sift4G	Pathogenic	0.0	D;D;D;D;D
Polyphen		1.0	D;.;.;.;.
Vest4		0.96
MutPred		0.93		Loss of MoRF binding (P = 0.0649);Loss of MoRF binding (P = 0.0649);Loss of MoRF binding (P = 0.0649);.;Loss of MoRF binding (P = 0.0649);
MVP		1.0
MPC		2.4
ClinPred		1.0	D
GERP RS		5.2
Varity_R		0.82
gMVP		0.99

Splicing

Name	Calibrated prediction	Score	Prediction
SpliceAI score (max)		0.010		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: rs1555226375; hg19: chr12-52164385;