rs397517729

Variant names:

• chr2-178561579-G-A
• rs397517729
• NM_001267550.2:c.84553C>T

Variant summary

Our verdict is Pathogenic. The variant received 11 ACMG points: 11P and 0B. PVS1 PM2 PP5

The NM_001267550.2(TTN):​c.84553C>T​(p.Arg28185*) 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 1,460,948 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 Conflicting classifications of pathogenicity (no stars). Variant results in nonsense mediated mRNA decay.

• Frequency:
  • Genomes: not found (cov: 33)
  • Exomes 𝑓: 6.8e-7 (0 hom.)
• Consequence: TTN NM_001267550.2 stop_gained
• Clinical Significance: Conflicting classifications of pathogenicity criteria provided, conflicting classifications P:4 U:1
• Conservation: PhyloP100: 2.72
• 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 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 2-178561579-G-A is Pathogenic according to our data. Variant chr2-178561579-G-A is described in ClinVar as Conflicting_classifications_of_pathogenicity. ClinVar VariationId is 47439.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	MANE	Protein	UniProt
TTN	NM_001267550.2	c.84553C>T	p.Arg28185*	stop_gained	Exon 326 of 363	ENST00000589042.5	NP_001254479.2

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	TSL	MANE	Protein	Appris	UniProt
TTN	ENST00000589042.5	c.84553C>T	p.Arg28185*	stop_gained	Exon 326 of 363	5	NM_001267550.2	ENSP00000467141.1

Frequencies

GnomAD3 genomes Cov.: 33

GnomAD4 exome AF: 6.84e-7 AC: 1 AN: 1460948 Hom.: 0 Cov.: 32 AF XY: 0.00 AC XY: 0 AN XY: 726712

African (AFR) AF: 0.00 AC: 0 AN: 33454

American (AMR) AF: 0.00 AC: 0 AN: 44660

Ashkenazi Jewish (ASJ) AF: 0.00 AC: 0 AN: 26106

East Asian (EAS) AF: 0.00 AC: 0 AN: 39578

South Asian (SAS) AF: 0.00 AC: 0 AN: 86174

European-Finnish (FIN) AF: 0.00 AC: 0 AN: 53344

Middle Eastern (MID) AF: 0.000174 AC: 1 AN: 5758

European-Non Finnish (NFE) AF: 0.00 AC: 0 AN: 1111528

Other (OTH) AF: 0.00 AC: 0 AN: 60346

GnomAD4 genome Cov.: 33

ClinVar

Significance: Conflicting classifications of pathogenicity

Submissions summary: Pathogenic:4 Uncertain:1

Revision: criteria provided, conflicting classifications

Submissions by phenotype

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

Feb 13, 2024

Labcorp Genetics (formerly Invitae), Labcorp

Significance: Likely pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

This sequence change creates a premature translational stop signal (p.Arg28185*) 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: 47439). 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. -

Dilated cardiomyopathy 1G Pathogenic:1

Jul 18, 2024

Institute of Human Genetics, Heidelberg University

Significance: Likely pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

- -

Primary familial dilated cardiomyopathy Pathogenic:1

Dec 17, 2024

Women's Health and Genetics/Laboratory Corporation of America, LabCorp

Significance: Likely pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

Variant summary: TTN NM_133378: c.76849C>T (p.Arg25617X) (also known as NM_001267550: c.84553C>T; p.Arg28185X ) results in a premature termination codon, predicted to cause a truncation of the encoded protein or absence of the protein due to nonsense mediated decay. Loss of function variants in all TTN bands are strongly associated with a spectrum of autosomal recessive titinopathies when exon expression (proportion spliced in, PSI, 1=complete expression) in skeletal muscle is >0.1 (PMID: 36977548, 39198997, 29598826, 32778822, 29691892, 33449170, 36977548, internal data). In contrast, loss of function variants in all TTN bands are only strongly associated with autosomal dominant TTN-related cardiomyopathies if located in exons constitutively expressed (PSI >0.9) in cardiac muscle, excluding extreme C-terminal exons 359-363 (PMID: 25589632, 31216868, 32964742, 34662387, 27869827, Shetty et al., Nat Cardiovasc Res 2024, cardiodb.org, internal data). This variant has a maximum skeletal muscle PSI of 0.968 and a maximum cardiac muscle PSI of 1.0. The variant was absent in 247794 control chromosomes (gnomAD). c.76849C>T has been reported in the literature without strong evidence for or against pathogenicity (examples: Connell_2021, Elfaith_2024). These report(s) do not provide unequivocal conclusions about association of the variant with Dilated Cardiomyopathy. To our knowledge, no experimental evidence demonstrating an impact on protein function has been reported. The following publications have been ascertained in the context of this evaluation (PMID: 33226272, 39020067). ClinVar contains an entry for this variant (Variation ID: 47439). Based on the evidence outlined above, the variant was classified as likely pathogenic for both autosomal dominant and autosomal recessive TTN-related conditions. -

Cardiovascular phenotype Pathogenic:1

Sep 05, 2024

Ambry Genetics

Significance: Likely pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

The p.R19120* variant (also known as c.57358C>T), located in coding exon 153 of the TTN gene, results from a C to T substitution at nucleotide position 57358. This changes the amino acid from an arginine to a stop codon within coding exon 153. 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. -

not specified Uncertain:1

Jun 26, 2012

Laboratory for Molecular Medicine, Mass General Brigham Personalized Medicine

Significance: Uncertain significance

Review Status: criteria provided, single submitter

Collection Method: clinical testing

Variant classified as Uncertain Significance - Favor Pathogenic. The Arg25617X v ariant in TTN has not been reported in the literature but has been detected by o ur laboratory in 1 infant with RCM of Arab ancestry who carried another cardiomy opathy variant of unknown significance. The Arg25617X variant leads to a prematu re termination codon at position 25617, which is predicted to lead to a truncate d or absent protein. Loss of function of the TTN gene is strongly associated wit h cardiomyopathy (DCM; Herman 2012). The Arg25617X variant is likely to severely impact the protein, but given that it has been detected in an individual with R CM (which is currently not associated with variants in TTN), additional studies are needed to determine its clinical significance. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
BayesDel_addAF	Pathogenic	0.54	D
BayesDel_noAF	Pathogenic	0.54
CADD	Pathogenic	65
DANN	Benign	0.97
Eigen	Pathogenic	0.74
Eigen_PC	Uncertain	0.58
FATHMM_MKL	Uncertain	0.96	D
PhyloP100		2.7
Vest4		0.96
GERP RS		4.2
Mutation Taster		=0/200	disease causing (fs/PTC)

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

Other links and lift over

dbSNP: rs397517729; hg19: chr2-179426306; COSMIC: COSV60137966; COSMIC: COSV60137966;