rs774604740

Positions:

• chr2-178570016-A-AT

Variant summary

Our verdict is Pathogenic. Variant got 11 ACMG points: 11P and 0B. PVS1 PM2 PP5

The NM_001267550.2(TTN):​c.76115_76116insA​(p.Asn25372LysfsTer5) 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 1,460,946 control chromosomes in the GnomAD database, with no homozygous occurrence. Variant has been reported in ClinVar as Conflicting classifications of pathogenicity (no stars). Variant results in nonsense mediated mRNA decay.

• Frequency:
  • Genomes: not found (cov: 33)
  • Exomes 𝑓: 0.0000014 (0 hom.)
• Consequence: TTN NM_001267550.2 frameshift
• Clinical Significance: Conflicting classifications of pathogenicity criteria provided, conflicting classifications P:6 U:1
• Conservation: PhyloP100: 2.09

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 11 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 2-178570016-A-AT is Pathogenic according to our data. Variant chr2-178570016-A-AT is described in ClinVar as [Conflicting_classifications_of_pathogenicity]. Clinvar id is 223383.We mark this variant Likely_pathogenic, oryginal submissions are: {Likely_pathogenic=3, Uncertain_significance=1, Pathogenic=3}.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	UniProt
TTN	NM_001267550.2	c.76115_76116insA	p.Asn25372LysfsTer5	frameshift_variant	326/363	ENST00000589042.5
TTN-AS1	NR_038272.1	n.2044-12552dup		intron_variant, non_coding_transcript_variant

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Appris	UniProt
TTN	ENST00000589042.5	c.76115_76116insA	p.Asn25372LysfsTer5	frameshift_variant	326/363	5	NM_001267550.2	P1
TTN-AS1	ENST00000659121.1	n.417-27576dup		intron_variant, non_coding_transcript_variant

Frequencies

GnomAD3 genomes Cov.: 33

GnomAD3 exomes AF: 0.00000404 AC: 1 AN: 247642 Hom.: 0 AF XY: 0.00000745 AC XY: 1 AN XY: 134318

Gnomad AFR exome AF: 0.00

Gnomad AMR exome AF: 0.00

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: 0.00000894

Gnomad OTH exome AF: 0.00

GnomAD4 exome AF: 0.00000137 AC: 2 AN: 1460946 Hom.: 0 Cov.: 40 AF XY: 0.00000138 AC XY: 1 AN XY: 726746

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: 0.00000180

Gnomad4 OTH exome AF: 0.00

GnomAD4 genome Cov.: 33

ClinVar

Significance: Conflicting classifications of pathogenicity

Submissions summary: Pathogenic:6 Uncertain:1

Revision: criteria provided, conflicting classifications

Submissions by phenotype

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

Likely pathogenic, criteria provided, single submitter

clinical testing

Invitae

Jan 28, 2023

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. 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). ClinVar contains an entry for this variant (Variation ID: 223383). This variant is also known as p.N23731Kfs*5. This premature translational stop signal has been observed in individual(s) with dilated cardiomyopathy (PMID: 25589632, 26406308, 29093449, 34587765). This variant is present in population databases (rs774604740, gnomAD 0.0009%). This sequence change creates a premature translational stop signal (p.Asn25372Lysfs*5) in the TTN gene. While this is not anticipated to result in nonsense mediated decay, it is expected to create a truncated TTN protein. -

Cardiomyopathy Pathogenic:1

Pathogenic, criteria provided, single submitter

clinical testing

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

Nov 08, 2022

- -

Dilated cardiomyopathy 1G Pathogenic:1

Likely pathogenic, criteria provided, single submitter

clinical testing

Invitae

Aug 30, 2016

This sequence change inserts 1 nucleotide in exon 326 of the TTN mRNA (c.76115dupA), causing a frameshift at codon 25372. This creates a premature translational stop signal (p.Asn25372Lysfs*5) and is expected to result in an absent or disrupted protein product. This variant is found in the A-band of this gene. This particular variant was reported in an individual with dilated cardiomyopathy (PMID: 25589632). Truncating variants in the A-band of TTN are significantly overrepresented in patients with dilated cardiomyopathy and are considered to be likely pathogenic for the disease (PMID: 25589632). ClinVar contains an entry for this variant (Variation ID: 223383). For these reasons, this variant has been classified as Likely Pathogenic. -

not provided Pathogenic:1

Pathogenic, criteria provided, single submitter

clinical testing

GeneDx

Mar 01, 2021

Identified in patients with DCM referred for genetic testing at GeneDx and in the literature (Roberts et al., 2015; Marston et al., 2015; Vikhorev et al., 2017); also denoted as c.76115dupA (p.Asn25372fs), p.N16499Kfs*5, and c.68408_68411del(A)4ins(A)5 (p.N22804K fs*5) due to the use of alternate transcripts and/or nomenclature; Not observed at a significant frequency in large population cohorts (Lek et al., 2016); 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; Located in the A-band region of titin, where the majority of truncating pathogenic variants associated with DCM have been reported (Herman et al., 2012); This variant is associated with the following publications: (PMID: 29093449, 25589632, 26406308) -

Primary dilated cardiomyopathy Pathogenic:1

Likely pathogenic, criteria provided, single submitter

research

Cardiovascular Biomedical Research Unit, Royal Brompton & Harefield NHS Foundation Trust

Oct 08, 2014

This TTN truncating variant (TTNtv) was identified in two individuals in this cohort and is located in an exon that is highly expressed in the heart. In the seven cohorts assessed, TTNtv were found in 14% of ambulant DCM, 22% end-stage or familial DCM, and 2% controls. Heterozygous nonsense, frameshift and canonical splice-disrupting variants found in constitutive and other highly utilised exons are highly likely to be pathogenic when identified in individuals with phenotypically confirmed DCM. TTNtv found incidentally in healthy individuals (excluding familial assessment of DCM relatives) are thought to have low penetrance, particularly when identified in exons that are not constitutively expressed in the heart. -

Cardiovascular phenotype Pathogenic:1

Pathogenic, criteria provided, single submitter

clinical testing

Ambry Genetics

Mar 13, 2024

The c.48920dupA pathogenic mutation, located in coding exon 153 of the TTN gene, results from a duplication of A at nucleotide position 48920, causing a translational frameshift with a predicted alternate stop codon (p.N16307Kfs*5). 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 (also referred to as p.Asn25372fs and p.N16499Kfs*5) was reported in individuals with features consistent with dilated cardiomyopathy (Roberts AM et al. Sci Transl Med, 2015 Jan;7:270ra6; Marston S et al. PLoS One, 2015 Sep;10:e0138568). 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 supporting evidence, this alteration is interpreted as a disease-causing mutation. -

TTN-related disorder Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Illumina Laboratory Services, Illumina

Aug 16, 2017

The TTN c.68411dupA (p.Asn22804LysfsTer5) variant results in a frameshift, and is predicted to result in premature termination of the protein. This variant has been reported in one study and is found in a heterozygous state in two individuals with dilated cardiomyopathy (Roberts et al. 2015). This variant has not been described in the literature in association with hereditary myopathy with early respiratory failure, hypertrophic cardiomyopathy, recessive limb-girdle muscular dystrophy, Salih myopathy, or Udd distal myopathy. The p.Asn22804LysfsTer5 was absent from 308 controls. The variant is reported at a frequency of 0.000009 in the European (non-Finnish) population of the Genome Aggregation Database but this is based on one allele in a region of good sequence coverage so the variant is presumed to be rare. Due to the limited evidence and potential impact of frameshift variants, the p.Asn22804LysfsTer5 variant is classified as a variant of unknown significance but suspicious for pathogenicity for TTN-related disorders. This variant was observed by ICSL as part of a predisposition screen in an ostensibly healthy population. -

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: rs774604740; hg19: chr2-179434743;