20-63359699-G-C

Variant names:

Variant summary

Our verdict is Uncertain significance. The variant received 0 ACMG points: 2P and 2B. PM2BP4_Moderate

The NM_000744.7(CHRNA4):c.77C>G(p.Ala26Gly) variant causes a missense, splice region change involving the alteration of a non-conserved nucleotide. The variant was absent in control chromosomes in GnomAD project. In-silico tool predicts a benign outcome for this variant. 17/24 in silico tools predict a benign outcome for this variant. 3/3 splice prediction tools predict no significant impact on normal splicing. Variant has been reported in ClinVar as Uncertain significance (★). Another variant affecting the same amino acid position, but resulting in a different missense (i.e. A26V) has been classified as Uncertain significance.

Frequency

Genomes: not found (cov: 34)

Exomes 𝑓: 6.9e-7 ( 0 hom. )

Failed GnomAD Quality Control

Consequence

CHRNA4
NM_000744.7 missense, splice_region

Scores

Splicing: ADA: 0.00004015

Clinical Significance

Uncertain significance criteria provided, single submitter U:1

Conservation

PhyloP100: -0.0510

Publications

0 publications found

Variant links:

Genes affected

CHRNA4 (HGNC:1958): (cholinergic receptor nicotinic alpha 4 subunit) This gene encodes a nicotinic acetylcholine receptor, which belongs to a superfamily of ligand-gated ion channels that play a role in fast signal transmission at synapses. These pentameric receptors can bind acetylcholine, which causes an extensive change in conformation that leads to the opening of an ion-conducting channel across the plasma membrane. This protein is an integral membrane receptor subunit that can interact with either nAChR beta-2 or nAChR beta-4 to form a functional receptor. Mutations in this gene cause nocturnal frontal lobe epilepsy type 1. Polymorphisms in this gene that provide protection against nicotine addiction have been described. Alternative splicing results in multiple transcript variants. [provided by RefSeq, Feb 2012]

CHRNA4 Gene-Disease associations (from GenCC):

autosomal dominant nocturnal frontal lobe epilepsy 1
Inheritance: AD Classification: DEFINITIVE, STRONG Submitted by: Labcorp Genetics (formerly Invitae), G2P
familial sleep-related hypermotor epilepsy
Inheritance: AD Classification: DEFINITIVE Submitted by: ClinGen
autosomal dominant nocturnal frontal lobe epilepsy
Inheritance: AD Classification: SUPPORTIVE Submitted by: Orphanet

CHRNA4 links:

Genome browser will be placed here

ACMG classification

Classification was made for transcript

Our verdict: Uncertain_significance. The variant received 0 ACMG points.

PM2

Very rare variant in population databases, with high coverage;

BP4

Computational evidence support a benign effect (MetaRNN=0.16818336).

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	MANE	Protein
CHRNA4	NM_000744.7 link	c.77C>G	p.Ala26Gly	missense_variant, splice_region_variant	Exon 2 of 6	ENST00000370263.9	NP_000735.1
CHRNA4	NM_001256573.2 link	c.-470C>G		splice_region_variant	Exon 2 of 6		NP_001243502.1
CHRNA4	NR_046317.2 link	n.261C>G		splice_region_variant, non_coding_transcript_exon_variant	Exon 2 of 6
CHRNA4	NM_001256573.2 link	c.-470C>G		5_prime_UTR_variant	Exon 2 of 6		NP_001243502.1

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	TSL	MANE	Protein	Appris	UniProt
CHRNA4	ENST00000370263.9 link	c.77C>G	p.Ala26Gly	missense_variant, splice_region_variant	Exon 2 of 6	1	NM_000744.7	ENSP00000359285.4

Frequencies

GnomAD3 genomes

Cov.:

GnomAD4 exome

Data not reliable, filtered out with message: AS_VQSR

AF:

6.86e-7

AC:

AN:

1458230

Hom.:

Cov.:

AF XY:

0.00000138

AC XY:

AN XY:

725444

show subpopulations

⚠️ The allele balance in gnomAD version 4 Exomes is significantly skewed from the expected value of 0.5.

African (AFR)

AF:

0.00

AC:

AN:

33428

American (AMR)

AF:

0.00

AC:

AN:

44704

Ashkenazi Jewish (ASJ)

AF:

0.00

AC:

AN:

26118

East Asian (EAS)

AF:

0.00

AC:

AN:

39694

South Asian (SAS)

AF:

0.00

AC:

AN:

86180

European-Finnish (FIN)

AF:

0.00

AC:

AN:

51682

Middle Eastern (MID)

AF:

0.00

AC:

AN:

4478

European-Non Finnish (NFE)

AF:

8.99e-7

AC:

AN:

1111766

Other (OTH)

AF:

0.00

AC:

AN:

60180

⚠️ The allele balance in gnomAD4 Exomes is highly skewed from 0.5 (p-value = 0), which strongly suggests a high chance of mosaicism in these individuals.

Allele Balance Distribution

Red line indicates average allele balance

Average allele balance: 0.375

Heterozygous variant carriers

0.00

0.20

0.40

0.60

0.80

0.95

Allele balance

GnomAD4 genome

Cov.:

Alfa

AF:

0.00

Hom.:

Bravo

AF:

0.00000756

EpiCase

AF:

0.0000545

EpiControl

AF:

0.00

ClinVar

Significance: Uncertain significance

Submissions summary: Uncertain:1

Revision: criteria provided, single submitter

LINK: link

Submissions by phenotype

Autosomal dominant nocturnal frontal lobe epilepsy

Uncertain:1

Mar 28, 2024

Labcorp Genetics (formerly Invitae), Labcorp

Significance:Uncertain significance

Review Status:criteria provided, single submitter

Collection Method:clinical testing

This sequence change replaces alanine, which is neutral and non-polar, with glycine, which is neutral and non-polar, at codon 26 of the CHRNA4 protein (p.Ala26Gly). This variant is not present in population databases (gnomAD no frequency). This variant has not been reported in the literature in individuals affected with CHRNA4-related conditions. Algorithms developed to predict the effect of missense changes on protein structure and function output the following: SIFT: "Not Available"; PolyPhen-2: "Benign"; Align-GVGD: "Not Available". The glycine amino acid residue is found in multiple mammalian species, which suggests that this missense change does not adversely affect protein function. 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

Benign

0.059

BayesDel_addAF

Benign

-0.11

BayesDel_noAF

Benign

-0.40

CADD

Benign

0.24

(source)

DANN

Benign

0.76

DEOGEN2

Benign

0.10

Eigen

Benign

-1.5

Eigen_PC

Benign

-1.6

FATHMM_MKL

Benign

0.081

LIST_S2

Benign

0.23

M_CAP

Pathogenic

0.91

MetaRNN

Benign

0.17

MetaSVM

Benign

-0.92

MutationAssessor

Benign

1.5

PhyloP100

-0.051

PrimateAI

Uncertain

0.59

PROVEAN

Benign

-0.27

REVEL

Benign

0.17

Sift

Benign

0.26

Sift4G

Benign

0.47

Polyphen

0.0090

Vest4

0.32

MutPred

0.33

Loss of stability (P = 0.0232);

MVP

0.47

MPC

0.61

ClinPred

0.19

GERP RS

-6.6

Varity_R

0.043

gMVP

0.45

Mutation Taster

=87/13

polymorphism

(source)

Splicing

Name

Calibrated prediction

Score

Prediction

dbscSNV1_ADA

Benign

0.000040

dbscSNV1_RF

Benign

0.11

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

Publications

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Variant summary

Frequency

Consequence

Scores

Clinical Significance

Conservation

Publications

ACMG classification

Transcripts

RefSeq

Ensembl

Frequencies

ClinVar

Submissions by phenotype

Computational scores

Splicing

Publications

Other links and lift over