chr20-63346768-G-C

Position:

• chr20-63346768-G-C

Variant summary

Our verdict is Uncertain significance. Variant got 4 ACMG points: 4P and 0B. PM2 PP3_Moderate

The NM_000744.7(CHRNA4):​c.1854C>G​(p.Phe618Leu) variant causes a missense change involving the alteration of a non-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: 33)
• Consequence: CHRNA4 NM_000744.7 missense
• Clinical Significance: Uncertain significance criteria provided, multiple submitters, no conflicts U:2
• Conservation: PhyloP100: 0.732

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]

ACMG classification

Verdict is Uncertain_significance. Variant got 4 ACMG points.

• PM2: Very rare variant in population databases, with high coverage
• PP3: MetaRNN computational evidence supports a deleterious effect, 0.859

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	UniProt
CHRNA4	NM_000744.7	c.1854C>G	p.Phe618Leu	missense_variant	6/6	ENST00000370263.9
CHRNA4	NM_001256573.2	c.1326C>G	p.Phe442Leu	missense_variant	6/6
CHRNA4	NR_046317.2	n.2063C>G		non_coding_transcript_exon_variant	6/6

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Appris	UniProt
CHRNA4	ENST00000370263.9	c.1854C>G	p.Phe618Leu	missense_variant	6/6	1	NM_000744.7	P1

Frequencies

GnomAD3 genomes Cov.: 33

GnomAD4 exome Cov.: 32

GnomAD4 genome Cov.: 33

ClinVar

Significance: Uncertain significance

Submissions summary: Uncertain:2

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

Autosomal dominant nocturnal frontal lobe epilepsy Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Labcorp Genetics (formerly Invitae), Labcorp

Nov 03, 2023

This sequence change replaces phenylalanine, which is neutral and non-polar, with leucine, which is neutral and non-polar, at codon 618 of the CHRNA4 protein (p.Phe618Leu). 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. ClinVar contains an entry for this variant (Variation ID: 565952). 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 not expected to disrupt CHRNA4 protein function with a negative predictive value of 80%. 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. -

Inborn genetic diseases Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Ambry Genetics

Sep 14, 2023

The c.1854C>G (p.F618L) alteration is located in exon 6 (coding exon 6) of the CHRNA4 gene. This alteration results from a C to G substitution at nucleotide position 1854, causing the phenylalanine (F) at amino acid position 618 to be replaced by a leucine (L). Based on insufficient or conflicting evidence, 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	0.20	D
BayesDel_noAF	Uncertain	0.060
CADD	Uncertain	24
DANN	Uncertain	1.0
DEOGEN2	Uncertain	0.66	D;.
Eigen	Uncertain	0.47
Eigen_PC	Uncertain	0.43
FATHMM_MKL	Uncertain	0.94	D
LIST_S2	Pathogenic	1.0	D;D
M_CAP	Pathogenic	0.53	D
MetaRNN	Pathogenic	0.86	D;D
MetaSVM	Uncertain	0.44	D
MutationAssessor	Uncertain	2.5	M;.
MutationTaster	Benign	1.0	D
PrimateAI	Uncertain	0.70	T
PROVEAN	Uncertain	-4.0	D;.
REVEL	Pathogenic	0.73
Sift	Benign	0.037	D;.
Sift4G	Benign	0.085	T;T
Polyphen		1.0	D;.
Vest4		0.75
MutPred		0.61		Gain of glycosylation at P621 (P = 0.1258);.;
MVP		0.87
MPC		1.3
ClinPred		0.99	D
GERP RS		4.4
Varity_R		0.49
gMVP		0.84

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

Publications

LitVar

Other links and lift over

dbSNP: rs1568805215; hg19: chr20-61978120;