rs876657666

chr2-178588815-T-TG

Variant summary

Our verdict is Pathogenic. Variant got 18 ACMG points: 18P and 0B. PVS1 PM2 PP5_Very_Strong

The NM_001267550.2(TTN):c.62909_62910insC(p.Glu20971ArgfsTer4) variant causes a frameshift change involving the alteration of a conserved nucleotide. The variant allele was found at a frequency of 0.00000205 in 1,461,208 control chromosomes in the GnomAD database, with no homozygous occurrence. Variant has been reported in ClinVar as Likely pathogenic (★★). Variant results in nonsense mediated mRNA decay.

• Frequency:
  • Genomes: not found (cov: 32)
  • Exomes 𝑓: 0.0000021 (0 hom.)
• Consequence: TTN NM_001267550.2 frameshift
• Clinical Significance: Likely pathogenic criteria provided, multiple submitters, no conflicts P:7
• Conservation: PhyloP100: 9.94

Genes affected

TTN (HGNC:12403): (titin) This gene encodes a large abundant protein of striated muscle. The product of this gene is divided into two regions, a N-terminal I-band and a C-terminal A-band. The I-band, which is the elastic part of the molecule, contains two regions of tandem immunoglobulin domains on either side of a PEVK region that is rich in proline, glutamate, valine and lysine. The A-band, which is thought to act as a protein-ruler, contains a mixture of immunoglobulin and fibronectin repeats, and possesses kinase activity. An N-terminal Z-disc region and a C-terminal M-line region bind to the Z-line and M-line of the sarcomere, respectively, so that a single titin molecule spans half the length of a sarcomere. Titin also contains binding sites for muscle associated proteins so it serves as an adhesion template for the assembly of contractile machinery in muscle cells. It has also been identified as a structural protein for chromosomes. Alternative splicing of this gene results in multiple transcript variants. Considerable variability exists in the I-band, the M-line and the Z-disc regions of titin. Variability in the I-band region contributes to the differences in elasticity of different titin isoforms and, therefore, to the differences in elasticity of different muscle types. Mutations in this gene are associated with familial hypertrophic cardiomyopathy 9, and autoantibodies to titin are produced in patients with the autoimmune disease scleroderma. [provided by RefSeq, Feb 2012]

TTN-AS1 (HGNC:44124): (TTN antisense RNA 1) This gene encodes a non-coding RNA transcribed from the opposite strand to the titin gene. [provided by RefSeq, Aug 2016]

ACMG classification

Verdict is Pathogenic. Variant got 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 2-178588815-T-TG is Pathogenic according to our data. Variant chr2-178588815-T-TG is described in ClinVar as [Likely_pathogenic]. Clinvar id is 228301.Status of the report is criteria_provided_multiple_submitters_no_conflicts, 2 stars.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	UniProt
TTN	NM_001267550.2	c.62909_62910insC	p.Glu20971ArgfsTer4	frameshift_variant	304/363	ENST00000589042.5
TTN-AS1	NR_038272.1	n.3189-2319dup		intron_variant, non_coding_transcript_variant

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Appris	UniProt
TTN	ENST00000589042.5	c.62909_62910insC	p.Glu20971ArgfsTer4	frameshift_variant	304/363	5	NM_001267550.2	P1
TTN-AS1	ENST00000659121.1	n.417-8776dup		intron_variant, non_coding_transcript_variant

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD4 exome AF: 0.00000205 AC: 3 AN: 1461208 Hom.: 0 Cov.: 33 AF XY: 0.00 AC XY: 0 AN XY: 726902

Gnomad4 AFR exome AF: 0.00

Gnomad4 AMR exome AF: 0.00

Gnomad4 ASJ exome AF: 0.00

Gnomad4 EAS exome AF: 0.00

Gnomad4 SAS exome AF: 0.00

Gnomad4 FIN exome AF: 0.00

Gnomad4 NFE exome AF: 0.00000270

Gnomad4 OTH exome AF: 0.00

GnomAD4 genome Cov.: 32

ClinVar

Significance: Likely pathogenic

Submissions summary: Pathogenic:7

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

not provided Pathogenic:2

Likely pathogenic, criteria provided, single submitter	clinical testing	Blueprint Genetics	Dec 28, 2017	- -
Likely pathogenic, criteria provided, single submitter	clinical testing	Eurofins Ntd Llc (ga)	Mar 20, 2018	- -

Autosomal recessive limb-girdle muscular dystrophy type 2J;C1858763:Dilated cardiomyopathy 1G Pathogenic:1

Likely pathogenic, criteria provided, single submitter

clinical testing

Invitae

Nov 10, 2023

This sequence change creates a premature translational stop signal (p.Glu20971Argfs*4) in the TTN gene. While this is not anticipated to result in nonsense mediated decay, it is expected to create a truncated TTN protein. This variant is not present in population databases (gnomAD no frequency). This variant has not been reported in the literature in individuals affected with TTN-related conditions. ClinVar contains an entry for this variant (Variation ID: 228301). This variant is located in the A band of TTN (PMID: 25589632). Truncating variants in this region are significantly overrepresented in patients affected with dilated cardiomyopathy (PMID: 25589632). Truncating variants in this region have also been reported in individuals affected with autosomal recessive centronuclear myopathy (PMID: 23975875). In summary, the currently available evidence indicates that the variant is pathogenic, but additional data are needed to prove that conclusively. Therefore, this variant has been classified as Likely Pathogenic. -

Cardiomyopathy Pathogenic:1

Likely pathogenic, criteria provided, single submitter

clinical testing

CHEO Genetics Diagnostic Laboratory, Children's Hospital of Eastern Ontario

Feb 18, 2022

- -

Dilated cardiomyopathy 1G Pathogenic:1

Likely pathogenic, criteria provided, single submitter

clinical testing

Clinical Genomics Laboratory, Washington University in St. Louis

Mar 29, 2024

The TTN c.62909dup (p.Glu20971ArgfsTer4) variant has been reported in one large scale study, but it was not specified if the identified individual was affected with a TTN-related disorder (Haggerty CM et al., PMID: 31216868). This variant has been reported in the ClinVar database as a germline likely pathogenic variant by five submitters. This variant causes a frameshift by duplicating a single nucleotide, leading to a premature termination codon, which is predicted to lead to nonsense mediated decay. This variant is located in the TTN protein A-band and truncating variants in this region are strongly associated with dilated cardiomyopathy (Rich KA et al., PMID: 32815318; Roberts AM et al., PMID: 25589632). Based on available information and the ACMG/AMP guidelines for variant interpretation (Richards S et al., PMID: 25741868), this variant is classified as likely pathogenic. -

Primary dilated cardiomyopathy Pathogenic:1

Likely pathogenic, criteria provided, single submitter

clinical testing

Laboratory for Molecular Medicine, Mass General Brigham Personalized Medicine

Feb 13, 2015

The p.Glu18403fs variant in TTN has not been previously reported in individuals with cardiomyopathy and was absent in large population studies. This variant is predicted to cause a frameshift, which alters the protein?s amino acid sequence beginning at position 18403 and leads to a premature termination codon 4 amino a cids downstream. This alteration is then predicted to lead to a truncated or abs ent protein. Frameshift and other truncating variants in TTN are strongly associ ated with DCM, particularly if they are located in the exons encoding for the A- band region of the protein (Herman 2012, Pugh 2014), where this variant is locat ed. In summary, although additional studies are required to fully establish its clinical significance, the p.Glu18403fs variant is likely pathogenic. -

Cardiovascular phenotype Pathogenic:1

Likely pathogenic, criteria provided, single submitter

clinical testing

Ambry Genetics

Oct 26, 2023

The c.35714dupC variant, located in coding exon 131 of the TTN gene, results from a duplication of C at nucleotide position 35714, causing a translational frameshift with a predicted alternate stop codon (p.E11906Rfs*4). This exon is located in the A-band region of the N2-B isoform of the titin protein and is constitutively expressed in TTN transcripts (percent spliced in or PSI 100%). This variant is considered to be rare based on population cohorts in the Genome Aggregation Database (gnomAD). This alteration is expected to result in loss of function by premature protein truncation or nonsense-mediated mRNA decay. While truncating variants in TTN are present in 1-3% of the general population, truncating variants in the A-band are the most common cause of dilated cardiomyopathy (DCM) (Herman DS et al. N. Engl. J. Med., 2012 Feb;366:619-28; Roberts AM et al. Sci Transl Med, 2015 Jan;7:270ra6). TTN truncating variants encoded in constitutive exons (PSI >90%) have been found to be significantly associated with DCM regardless of their position in titin (Schafer S et al. Nat. Genet., 2017 01;49:46-53). Based on the majority of available evidence to date, this variant is likely to be pathogenic. -

Computational scores

Source: dbNSFP v4.3

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: rs876657666; hg19: chr2-179453542;