2-166046888-G-T

Variant names:

• chr2-166046888-G-T
• rs794726826
• NM_001165963.4:c.1259C>A

Variant summary

Our verdict is Pathogenic. The variant received 12 ACMG points: 12P and 0B. PM1 PM2 PM5 PP2 PP3_Strong PP5

The NM_001165963.4(SCN1A):​c.1259C>A​(p.Ala420Asp) 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. 13/22 in silico tools predict a damaging outcome for this variant. Variant has been reported in ClinVar as Conflicting classifications of pathogenicity (no stars). Another variant affecting the same amino acid position, but resulting in a different missense (i.e. A420V) has been classified as Pathogenic.

• Frequency: Genomes: not found (cov: 32)
• Consequence: SCN1A NM_001165963.4 missense
• Clinical Significance: Conflicting classifications of pathogenicity criteria provided, conflicting classifications P:1 U:1
• Conservation: PhyloP100: 10.0
• Publications: 3 publications found

Genes affected

SCN1A (HGNC:10585): (sodium voltage-gated channel alpha subunit 1) Voltage-dependent sodium channels are heteromeric complexes that regulate sodium exchange between intracellular and extracellular spaces and are essential for the generation and propagation of action potentials in muscle cells and neurons. Each sodium channel is composed of a large pore-forming, glycosylated alpha subunit and two smaller beta subunits. This gene encodes a sodium channel alpha subunit, which has four homologous domains, each of which contains six transmembrane regions. Allelic variants of this gene are associated with generalized epilepsy with febrile seizures and epileptic encephalopathy. Alternative splicing results in multiple transcript variants. The RefSeq Project has decided to create four representative RefSeq records. Three of the transcript variants are supported by experimental evidence and the fourth contains alternate 5' untranslated exons, the exact combination of which have not been experimentally confirmed for the full-length transcript. [provided by RefSeq, Oct 2015]

SCN1A-AS1 (HGNC:54069): (SCN1A and SCN9A antisense RNA 1)

ACMG classification

Our verdict: Pathogenic. The variant received 12 ACMG points.

• PM1: In a hotspot region, there are 15 aminoacids with missense pathogenic changes in the window of +-8 aminoacids around while only 0 benign, 7 uncertain in NM_001165963.4
• PM2: Very rare variant in population databases, with high coverage
• PM5: Other missense variant is known to change same aminoacid residue: Variant chr2-166046888-G-A is described in ClinVar as Pathogenic. ClinVar VariationId is 189996.Status of the report is criteria_provided_multiple_submitters_no_conflicts, 2 stars.
• PP2: Missense variant in the SCN1A gene, where missense mutations are typically associated with disease (based on misZ statistic). The gene has 848 curated pathogenic missense variants (we use a threshold of 10). The gene has 89 curated benign missense variants. Gene score misZ: 5.2206 (above the threshold of 3.09). Trascript score misZ: 7.6022 (above the threshold of 3.09). GenCC associations: The gene is linked to familial or sporadic hemiplegic migraine, myoclonic-astatic epilepsy, arthrogryposis, Dravet syndrome, malignant migrating partial seizures of infancy, generalized epilepsy with febrile seizures plus, type 2, migraine, familial hemiplegic, 3, developmental and epileptic encephalopathy, 6A, familial hemiplegic migraine, generalized epilepsy with febrile seizures plus, genetic developmental and epileptic encephalopathy, Lennox-Gastaut syndrome.
• PP3: MetaRNN computational evidence supports a deleterious effect, 0.957
• PP5: Variant 2-166046888-G-T is Pathogenic according to our data. Variant chr2-166046888-G-T is described in ClinVar as Conflicting_classifications_of_pathogenicity. ClinVar VariationId is 283002.

Variant Effect in Transcripts

ACMG analysis was done for transcript: NM_001165963.4. You can select a different transcript below to see updated ACMG assignments.

RefSeq Transcripts

Selected	Gene	Transcript	Tags	HGVSc	HGVSp	Effect	Exon Rank	Protein	UniProt
	SCN1A	NM_001165963.4	MANE Select	c.1259C>A	p.Ala420Asp	missense	Exon 12 of 29	NP_001159435.1
	SCN1A	NM_001353961.2		c.-1167C>A		5_prime_UTR_premature_start_codon_gain	Exon 11 of 28	NP_001340890.1
	SCN1A	NM_001202435.3		c.1259C>A	p.Ala420Asp	missense	Exon 11 of 28	NP_001189364.1

Ensembl Transcripts

Selected	Gene	Transcript	Tags	HGVSc	HGVSp	Effect	Exon Rank	Protein	UniProt
	SCN1A	ENST00000674923.1	MANE Select	c.1259C>A	p.Ala420Asp	missense	Exon 12 of 29	ENSP00000501589.1
	SCN1A	ENST00000303395.9	TSL:5	c.1259C>A	p.Ala420Asp	missense	Exon 11 of 28	ENSP00000303540.4
	SCN1A	ENST00000375405.7	TSL:5	c.1259C>A	p.Ala420Asp	missense	Exon 9 of 26	ENSP00000364554.3

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD4 exome Cov.: 32

GnomAD4 genome Cov.: 32

ClinVar

Significance: Conflicting classifications of pathogenicity

Submissions summary: Pathogenic:1 Uncertain:1

Revision: criteria provided, conflicting classifications

Submissions by phenotype

Developmental and epileptic encephalopathy 6B Pathogenic:1

Aug 24, 2021

Breda Genetics srl

Significance: Likely pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

The variant c.1259C>A (p.Ala420Asp) in the SCN1A gene is reported as uncertain in ClinVar (Variation ID:283002). The variant has been reported as likely pathogenic by Butler et al. (2017) in a patient with epilepsy whose detailed phenotype was not available. Furthermore, the variant falls into a region rich in missense mutations reported as pathogenic or likely pathogenic (Clinvar), one of which affects the same nucelotide, causing a different amino acid change (c.1259C>T, p.Ala420Val, Clinvar variation ID:189996). There is no information on frequency in gnomAD database. The nucleotide position is conserved across 35 mammalian species(GERP RS: 5.31). In silico analysis indicates that the variant might be damaging.

not provided Uncertain:1

Aug 28, 2015

Eurofins Ntd Llc (ga)

Significance: Uncertain significance

Review Status: criteria provided, single submitter

Collection Method: clinical testing

Computational scores

Source: dbNSFP v4.9

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Pathogenic	1.0
BayesDel_addAF	Pathogenic	0.57	D
BayesDel_noAF	Pathogenic	0.58
CADD	Pathogenic	28
DANN	Uncertain	1.0
DEOGEN2	Pathogenic	0.99	D
Eigen	Pathogenic	1.2
Eigen_PC	Pathogenic	1.0
FATHMM_MKL	Uncertain	0.97	D
LIST_S2	Pathogenic	0.97	D
M_CAP	Pathogenic	0.98	D
MetaRNN	Pathogenic	0.96	D
MetaSVM	Pathogenic	0.97	D
MutationAssessor	Pathogenic	4.5	H
PhyloP100		10
PrimateAI	Pathogenic	0.91	D
PROVEAN	Pathogenic	-5.9	D
REVEL	Pathogenic	0.96
Sift	Pathogenic	0.0	D
Sift4G	Pathogenic	0.0	D
Polyphen		1.0	D
Vest4		0.99
MutPred		0.78		Loss of stability (P = 0.1562)
MVP		1.0
MPC		2.1
ClinPred		1.0	D
GERP RS		5.3
Varity_R		0.96
gMVP		1.0
Mutation Taster		=0/100	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: rs794726826; hg19: chr2-166903398;