7-143319794-C-T

Variant names:

• chr7-143319794-C-T
• rs1554434400
• NM_000083.3:c.220C>T

Variant summary

Our verdict is Pathogenic. The variant received 18 ACMG points: 18P and 0B. PVS1 PM2 PP5_Very_Strong

The NM_000083.3(CLCN1):​c.220C>T​(p.Gln74*) variant causes a stop gained change involving the alteration of a non-conserved nucleotide. The variant allele was found at a frequency of 0.000000684 in 1,460,930 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 Pathogenic (★★). Variant results in nonsense mediated mRNA decay.

• Frequency:
  • Genomes: not found (cov: 32)
  • Exomes 𝑓: 6.8e-7 (0 hom.)
• Consequence: CLCN1 NM_000083.3 stop_gained
• Clinical Significance: Pathogenic criteria provided, multiple submitters, no conflicts P:2
• Conservation: PhyloP100: 0.169
• Publications: 0 publications found

Genes affected

CLCN1 (HGNC:2019): (chloride voltage-gated channel 1) The CLCN family of voltage-dependent chloride channel genes comprises nine members (CLCN1-7, Ka and Kb) which demonstrate quite diverse functional characteristics while sharing significant sequence homology. The protein encoded by this gene regulates the electric excitability of the skeletal muscle membrane. Mutations in this gene cause two forms of inherited human muscle disorders: recessive generalized myotonia congenita (Becker) and dominant myotonia (Thomsen). Alternative splicing results in multiple transcript variants. [provided by RefSeq, Mar 2012]

CLCN1 Gene-Disease associations (from GenCC):

• myotonia congenita, autosomal dominant

  Inheritance: AD Classification: STRONG Submitted by: Genomics England PanelApp, Labcorp Genetics (formerly Invitae)
• myotonia congenita, autosomal recessive

  Inheritance: AR Classification: STRONG Submitted by: Labcorp Genetics (formerly Invitae), Genomics England PanelApp
• Thomsen and Becker disease

  Inheritance: AD Classification: SUPPORTIVE Submitted by: Orphanet

ACMG classification

Our verdict: Pathogenic. The variant received 18 ACMG points.

• PVS1: Loss of function variant, product undergoes nonsense mediated mRNA decay. LoF is a known mechanism of disease.
• PM2: Very rare variant in population databases, with high coverage
• PP5: Variant 7-143319794-C-T is Pathogenic according to our data. Variant chr7-143319794-C-T is described in ClinVar as Pathogenic. ClinVar VariationId is 462829.Status of the report is criteria_provided_multiple_submitters_no_conflicts, 2 stars.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	MANE	Protein	UniProt
CLCN1	NM_000083.3	c.220C>T	p.Gln74*	stop_gained	Exon 2 of 23	ENST00000343257.7	NP_000074.3
CLCN1	NR_046453.2	n.322C>T		non_coding_transcript_exon_variant	Exon 2 of 22

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	TSL	MANE	Protein	Appris	UniProt
CLCN1	ENST00000343257.7	c.220C>T	p.Gln74*	stop_gained	Exon 2 of 23	1	NM_000083.3	ENSP00000339867.2
CLCN1	ENST00000650516.2	c.220C>T	p.Gln74*	stop_gained	Exon 2 of 23			ENSP00000498052.2
CLCN1	ENST00000432192.6	n.-15C>T		upstream_gene_variant		1		ENSP00000395949.2

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD4 exome AF: 6.84e-7 AC: 1 AN: 1460930 Hom.: 0 Cov.: 31 AF XY: 0.00000138 AC XY: 1 AN XY: 726838

African (AFR) AF: 0.00 AC: 0 AN: 33458

American (AMR) AF: 0.00 AC: 0 AN: 44722

Ashkenazi Jewish (ASJ) AF: 0.00 AC: 0 AN: 26128

East Asian (EAS) AF: 0.00 AC: 0 AN: 39696

South Asian (SAS) AF: 0.00 AC: 0 AN: 86230

European-Finnish (FIN) AF: 0.00 AC: 0 AN: 53416

Middle Eastern (MID) AF: 0.00 AC: 0 AN: 5764

European-Non Finnish (NFE) AF: 9.00e-7 AC: 1 AN: 1111162

Other (OTH) AF: 0.00 AC: 0 AN: 60354

GnomAD4 genome Cov.: 32

ClinVar

Significance: Pathogenic

Submissions summary: Pathogenic:2

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

Congenital myotonia, autosomal recessive form;C2936781:Congenital myotonia, autosomal dominant form Pathogenic:1

May 06, 2024

Labcorp Genetics (formerly Invitae), Labcorp

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

This sequence change creates a premature translational stop signal (p.Gln74*) in the CLCN1 gene. It is expected to result in an absent or disrupted protein product. Loss-of-function variants in CLCN1 are known to be pathogenic (PMID: 17932099, 22094069, 23739125). This variant is not present in population databases (gnomAD no frequency). This premature translational stop signal has been observed in individuals with autosomal recessive Becker-type myotonia (PMID: 8571958, 24349310). ClinVar contains an entry for this variant (Variation ID: 462829). Algorithms developed to predict the effect of sequence changes on RNA splicing suggest that this variant may disrupt the consensus splice site. For these reasons, this variant has been classified as Pathogenic.

Congenital myotonia, autosomal recessive form Pathogenic:1

Nov 23, 2021

MGZ Medical Genetics Center

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
BayesDel_addAF	Pathogenic	0.63	D
BayesDel_noAF	Uncertain	0.020
CADD	Pathogenic	26
DANN	Uncertain	0.98
DEOGEN2	Benign	0.0	.;.
Eigen	Benign	-0.25
Eigen_PC	Benign	-0.55
LIST_S2	Benign	0.0	.;.
MetaRNN	Benign	0.0	.;.
MutationAssessor	Benign	0.0	.;.
PhyloP100		0.17
PROVEAN	Benign	0.0	.;.
Sift	Pathogenic	0.0	.;.
Sift4G	Pathogenic	0.0	.;.
Vest4		0.0
GERP RS		2.3
Mutation Taster		=5/195	disease causing (ClinVar)

Splicing

Name	Calibrated prediction	Score	Prediction
SpliceAI score (max)		0.36		Details are displayed if max score is > 0.2
DS_AL_spliceai		0.36		Position offset: -39

Find out detailed SpliceAI scores and Pangolin per-transcript scores at spliceailookup.broadinstitute.org

Other links and lift over

dbSNP: rs1554434400; hg19: chr7-143016887;