chrX-71223765-A-G

Position:

• chrX-71223765-A-G

Variant summary

Our verdict is Likely pathogenic. Variant got 6 ACMG points: 6P and 0B. PM1 PM2 PM5

The NM_000166.6(GJB1):​c.58A>G​(p.Ile20Val) variant causes a missense change involving the alteration of a non-conserved nucleotide. The variant was absent in control chromosomes in GnomAD project. 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. I20F) has been classified as Pathogenic.

• Frequency: Genomes: not found (cov: 22)
• Consequence: GJB1 NM_000166.6 missense
• Clinical Significance: Uncertain significance criteria provided, single submitter U:1
• Conservation: PhyloP100: 3.23

Genes affected

GJB1 (HGNC:4283): (gap junction protein beta 1) This gene encodes a member of the gap junction protein family. The gap junction proteins are membrane-spanning proteins that assemble to form gap junction channels that facilitate the transfer of ions and small molecules between cells. According to sequence similarities at the nucleotide and amino acid levels, the gap junction proteins are divided into two categories, alpha and beta. Mutations in this gene cause X-linked Charcot-Marie-Tooth disease, an inherited peripheral neuropathy. Alternatively spliced transcript variants encoding the same protein have been found for this gene. [provided by RefSeq, Oct 2008]

ACMG classification

Verdict is Likely_pathogenic. Variant got 6 ACMG points.

• PM1: In a hotspot region, there are 13 aminoacids with missense pathogenic changes in the window of +-8 aminoacids around while only 0 benign, 14 uncertain in NM_000166.6
• PM2: Very rare variant in population databases, with high coverage
• PM5: Other missense variant is known to change same aminoacid residue: Variant chrX-71223766-T-C is described in ClinVar as [Likely_pathogenic]. Clinvar id is 581956.Status of the report is criteria_provided_single_submitter, 1 stars.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	UniProt
GJB1	NM_000166.6	c.58A>G	p.Ile20Val	missense_variant	2/2	ENST00000361726.7
GJB1	NM_001097642.3	c.58A>G	p.Ile20Val	missense_variant	2/2
GJB1	XM_011530907.3	c.58A>G	p.Ile20Val	missense_variant	2/2

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Appris	UniProt
GJB1	ENST00000361726.7	c.58A>G	p.Ile20Val	missense_variant	2/2	1	NM_000166.6	P1

Frequencies

GnomAD3 genomes Cov.: 22

GnomAD4 exome Cov.: 31

GnomAD4 genome Cov.: 22

ClinVar

Significance: Uncertain significance

Submissions summary: Uncertain:1

Revision: criteria provided, single submitter

Submissions by phenotype

Charcot-Marie-Tooth Neuropathy X Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Labcorp Genetics (formerly Invitae), Labcorp

Feb 15, 2020

This sequence change replaces isoleucine with valine at codon 20 of the GJB1 protein (p.Ile20Val). The isoleucine residue is highly conserved and there is a small physicochemical difference between isoleucine and valine. This variant is not present in population databases (ExAC no frequency). 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. Other missense substitutions at this codon (p.Ile20Phe, p.Ile20Ser, and p.Ile20Thr) have been reported in individuals affected with Charcot-Marie-Tooth disease (PMID: 27844031, 9361298, 24484554) Algorithms developed to predict the effect of missense changes on protein structure and function do not agree on the potential impact of this missense change (SIFT: "Deleterious"; PolyPhen-2: "Benign"; Align-GVGD: "Class C0"). This variant has not been reported in the literature in individuals with GJB1-related disease. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Benign	0.10
BayesDel_addAF	Uncertain	0.11	D
BayesDel_noAF	Uncertain	-0.080
CADD	Benign	22
DANN	Benign	0.97
DEOGEN2	Uncertain	0.76	D;D;D;D;T;.;D
FATHMM_MKL	Uncertain	0.82	D
LIST_S2	Benign	0.79	.;.;.;.;T;T;T
M_CAP	Pathogenic	0.60	D
MetaRNN	Uncertain	0.69	D;D;D;D;D;D;D
MetaSVM	Pathogenic	0.99	D
MutationAssessor	Benign	1.4	L;L;L;L;.;.;L
MutationTaster	Benign	1.0	D;D;D
PrimateAI	Uncertain	0.54	T
PROVEAN	Benign	-0.96	N;.;N;.;N;.;N
REVEL	Uncertain	0.53
Sift	Benign	0.071	T;.;T;.;T;.;T
Sift4G	Benign	0.22	T;.;T;.;T;.;T
Polyphen		0.36	B;B;B;B;.;.;B
Vest4		0.38
MutPred		0.70		Gain of sheet (P = 0.0827);Gain of sheet (P = 0.0827);Gain of sheet (P = 0.0827);Gain of sheet (P = 0.0827);Gain of sheet (P = 0.0827);Gain of sheet (P = 0.0827);Gain of sheet (P = 0.0827);
MVP		0.81
MPC		0.66
ClinPred		0.55	D
GERP RS		4.4
Varity_R		0.51
gMVP		0.91

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: rs1555937019; hg19: chrX-70443615;