rs757603460

Positions:

• chr2-178577446-G-GGTAT

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.68888_68889insATAC​(p.Ile22964TyrfsTer8) variant causes a frameshift change. The variant was absent in control chromosomes in GnomAD project. Variant has been reported in ClinVar as Likely pathogenic (★★). Variant results in nonsense mediated mRNA decay.

• Frequency:
  • Genomes: not found (cov: 32)
  • Exomes 𝑓: 0.0000014 (0 hom.)
  • Failed GnomAD Quality Control
• Consequence: TTN NM_001267550.2 frameshift
• Clinical Significance: Pathogenic/Likely pathogenic criteria provided, multiple submitters, no conflicts P:4
• Conservation: PhyloP100: 4.88

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]

(HGNC:):

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 2-178577446-G-GGTAT is Pathogenic according to our data. Variant chr2-178577446-G-GGTAT is described in ClinVar as [Likely_pathogenic]. Clinvar id is 404732.Status of the report is criteria_provided_multiple_submitters_no_conflicts, 2 stars.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
TTN	NM_001267550.2	c.68888_68889insATAC	p.Ile22964TyrfsTer8	frameshift_variant	324/363	ENST00000589042.5	NP_001254479.2
TTN-AS1	NR_038272.1	n.2044-5125_2044-5122dup		intron_variant, non_coding_transcript_variant

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
TTN	ENST00000589042.5	c.68888_68889insATAC	p.Ile22964TyrfsTer8	frameshift_variant	324/363	5	NM_001267550.2	ENSP00000467141	P1
	ENST00000604215.1	n.345_348dup		non_coding_transcript_exon_variant	1/1
TTN-AS1	ENST00000659121.1	n.417-20149_417-20146dup		intron_variant, non_coding_transcript_variant

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD3 exomes AF: 0.00000812 AC: 2 AN: 246420 Hom.: 0 AF XY: 0.00 AC XY: 0 AN XY: 133920

Gnomad AFR exome AF: 0.00

Gnomad AMR exome AF: 0.0000581

Gnomad ASJ exome AF: 0.00

Gnomad EAS exome AF: 0.00

Gnomad SAS exome AF: 0.00

Gnomad FIN exome AF: 0.00

Gnomad NFE exome AF: 0.00

Gnomad OTH exome AF: 0.00

GnomAD4 exome Data not reliable, filtered out with message: AS_VQSR AF: 0.00000137 AC: 2 AN: 1454750 Hom.: 0 Cov.: 35 AF XY: 0.00 AC XY: 0 AN XY: 722612

Gnomad4 AFR exome AF: 0.00

Gnomad4 AMR exome AF: 0.0000448

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: 0.00

Gnomad4 OTH exome AF: 0.00

GnomAD4 genome Cov.: 32

ClinVar

Significance: Pathogenic/Likely pathogenic

Submissions summary: Pathogenic:4

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

not provided Pathogenic:2

Likely pathogenic, criteria provided, single submitter	clinical testing	Eurofins Ntd Llc (ga)	Jul 15, 2016	The c.61181_61184dupATAC TTN variant has not been reported in individuals with disease. The c.61181_61184dupATAC variant is located in the A-band region of the TTN protein.1 While truncating variants in this region have been reported in individuals in the general population, they have also been reported at a significantly higher frequency in individuals with dilated cardiomyopathy (DCM).1,2 Therefore, the c.61181_61184dupATAC TTN variant is classified as likely pathogenic. 1. Herman et al. N Engl J Med. 2012 Feb 16;366(7):619-28. 2. Pugh et al. Genet Med. 2014 Aug;16(8):601-8. AKT 7-15-16 -
Pathogenic, criteria provided, single submitter	clinical testing	GeneDx	Nov 25, 2022	Frameshift variant predicted to result in protein truncation or nonsense mediated decay in a gene for which loss of function is a known mechanism of disease; Not observed at significant frequency in large population cohorts (gnomAD); Located in the A-band region of TTN in which the majority of loss of function variants have been associated with autosomal dominant titinopathies (Herman et al., 2012); Has not been previously published as pathogenic or benign to our knowledge -

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

Likely pathogenic, criteria provided, single submitter

clinical testing

Labcorp Genetics (formerly Invitae), Labcorp

Jan 05, 2024

This sequence change creates a premature translational stop signal (p.Ile22964Tyrfs*8) 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 present in population databases (rs757603460, gnomAD 0.006%). This premature translational stop signal has been observed in individual(s) with dilated cardiomyopathy (Invitae). ClinVar contains an entry for this variant (Variation ID: 404732). 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. -

Cardiovascular phenotype Pathogenic:1

Likely pathogenic, criteria provided, single submitter

clinical testing

Ambry Genetics

May 30, 2023

The c.41690_41693dupATAC variant, located in coding exon 151 of the TTN gene, results from a duplication of ATAC at nucleotide position 41690, causing a translational frameshift with a predicted alternate stop codon (p.I13899Yfs*8). 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 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). As such, this alteration is classified as likely pathogenic. -

Computational scores

Source: dbNSFP v4.3

Splicing

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

Publications

LitVar

Other links and lift over

dbSNP: rs757603460; hg19: chr2-179442173;