chr2-178569952-A-AAGGAGGGCTTGGTTCACTAAGTT

Variant names:

• chr2-178569952-A-AAGGAGGGCTTGGTTCACTAAGTT
• rs878854335
• NM_001267550.2:c.76179_76180insAACTTAGTGAACCAAGCCCTCCT

Variant summary

Our verdict is Pathogenic. The variant received 16 ACMG points: 16P and 0B. PVS1 PP5_Very_Strong

The NM_001267550.2(TTN):​c.76179_76180insAACTTAGTGAACCAAGCCCTCCT​(p.Ser25394AsnfsTer30) variant causes a frameshift change involving the alteration of a non-conserved nucleotide. The variant allele was found at a frequency of 0.00000137 in 1,460,424 control chromosomes in the GnomAD database, with no homozygous occurrence. It is difficult to determine the true allele frequency of this variant because it is of type INS_BIG, and the frequency of such variant types in population databases may be underestimated and unreliable. Variant has been reported in ClinVar as Pathogenic (★★). Synonymous variant affecting the same amino acid position (i.e. P25393P) has been classified as Likely benign. Variant results in nonsense mediated mRNA decay.

• Frequency:
  • Genomes: not found (cov: 32)
  • Exomes 𝑓: 0.0000014 (0 hom.)
• Consequence: TTN NM_001267550.2 frameshift
• Clinical Significance: Pathogenic criteria provided, multiple submitters, no conflicts P:3
• Conservation: PhyloP100: 1.92
• Publications: 0 publications found

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

Our verdict: Pathogenic. The variant received 16 ACMG points.

• PVS1: Loss of function variant, product undergoes nonsense mediated mRNA decay. LoF is a known mechanism of disease.
• PP5: Variant 2-178569952-A-AAGGAGGGCTTGGTTCACTAAGTT is Pathogenic according to our data. Variant chr2-178569952-A-AAGGAGGGCTTGGTTCACTAAGTT is described in ClinVar as Pathogenic. ClinVar VariationId is 238845.Status of the report is criteria_provided_multiple_submitters_no_conflicts, 2 stars.

Variant Effect in Transcripts

ACMG analysis was done for transcript: NM_001267550.2. You can select a different transcript below to see updated ACMG assignments.

RefSeq Transcripts

Selected	Gene	Transcript	Tags	HGVSc	HGVSp	Effect	Exon Rank	Protein	UniProt
	TTN	NM_001267550.2	MANE Select	c.76179_76180insAACTTAGTGAACCAAGCCCTCCT	p.Ser25394AsnfsTer30	frameshift	Exon 326 of 363	NP_001254479.2
	TTN	NM_001256850.1		c.71256_71257insAACTTAGTGAACCAAGCCCTCCT	p.Ser23753AsnfsTer30	frameshift	Exon 276 of 313	NP_001243779.1
	TTN	NM_133378.4		c.68475_68476insAACTTAGTGAACCAAGCCCTCCT	p.Ser22826AsnfsTer30	frameshift	Exon 275 of 312	NP_596869.4

Ensembl Transcripts

Selected	Gene	Transcript	Tags	HGVSc	HGVSp	Effect	Exon Rank	Protein	UniProt
	TTN	ENST00000589042.5	TSL:5 MANE Select	c.76179_76180insAACTTAGTGAACCAAGCCCTCCT	p.Ser25394AsnfsTer30	frameshift	Exon 326 of 363	ENSP00000467141.1
	TTN	ENST00000446966.2	TSL:1	c.76023_76024insAACTTAGTGAACCAAGCCCTCCT	p.Ser25342AsnfsTer30	frameshift	Exon 324 of 361	ENSP00000408004.2
	TTN	ENST00000436599.2	TSL:1	c.75903_75904insAACTTAGTGAACCAAGCCCTCCT	p.Ser25302AsnfsTer30	frameshift	Exon 324 of 361	ENSP00000405517.2

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD4 exome AF: 0.00000137 AC: 2 AN: 1460424 Hom.: 0 Cov.: 40 AF XY: 0.00000275 AC XY: 2 AN XY: 726366

African (AFR) AF: 0.00 AC: 0 AN: 33426

American (AMR) AF: 0.00 AC: 0 AN: 44658

Ashkenazi Jewish (ASJ) AF: 0.00 AC: 0 AN: 26078

East Asian (EAS) AF: 0.00 AC: 0 AN: 39588

South Asian (SAS) AF: 0.00 AC: 0 AN: 86142

European-Finnish (FIN) AF: 0.00 AC: 0 AN: 53340

Middle Eastern (MID) AF: 0.00 AC: 0 AN: 5750

European-Non Finnish (NFE) AF: 0.00000180 AC: 2 AN: 1111142

Other (OTH) AF: 0.00 AC: 0 AN: 60300

GnomAD4 genome Cov.: 32

ClinVar

Significance: Pathogenic

Submissions summary: Pathogenic:3

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

Dilated cardiomyopathy 1G Pathogenic:1

Mar 08, 2016

Labcorp Genetics (formerly Invitae), Labcorp

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

This sequence change inserts 23 nucleotides in exon 326 of the TTN mRNA (c.76179_76180ins23), causing a frameshift at codon 25394. This creates a premature translational stop signal (p.Ser25394Asnfs*30) and is expected to result in an absent or disrupted protein product. This variant is found in the A-band of this gene. Truncating variants in the A-band of TTN are likely pathogenic (PMID: 25589632). This particular variant has been already found in an individual with personal and family history of dilated cardiomyopathy (Invitae database). For these reasons, this variant has been classified as Pathogenic.

not provided Pathogenic:1

Oct 27, 2016

Molecular Diagnostic Laboratory for Inherited Cardiovascular Disease, Montreal Heart Institute

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

Cardiovascular phenotype Pathogenic:1

Jul 18, 2025

Ambry Genetics

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

The c.48984_48985ins23 pathogenic mutation, located in coding exon 153 of the TTN gene, results from an insertion of 23 nucleotides at position 48984, causing a translational frameshift with a predicted alternate stop codon (p.S16329Nfs*30). 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 was reported in individual(s) with features consistent with dilated cardiomyopathy (external communication; Ambry internal data). This variant is considered to be rare based on population cohorts in the Genome Aggregation Database (gnomAD). This variant 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 (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; Akhtar MM et al. Circ Heart Fail, 2020 Oct;13:e006832; Massier M et al. Clin Genet, 2025 Jan). Based on the supporting evidence, this variant is interpreted as a disease-causing mutation.

Computational scores

Source: dbNSFP v4.9

Name	Calibrated prediction	Score	Prediction
PhyloP100		1.9
Mutation Taster		=0/200	disease causing (ClinVar)

Splicing

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

Other links and lift over

dbSNP: rs878854335; hg19: chr2-179434679;