rs794729275

Positions:

• chr2-178595585-G-A

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.57769C>T​(p.Arg19257Ter) variant causes a stop gained change. The variant allele was found at a frequency of 0.0000035 in 1,429,394 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 Likely pathogenic (★★). Variant results in nonsense mediated mRNA decay.

• Frequency:
  • Genomes: not found (cov: 32)
  • Exomes 𝑓: 0.0000035 (0 hom.)
• Consequence: TTN NM_001267550.2 stop_gained
• Clinical Significance: Pathogenic/Likely pathogenic criteria provided, multiple submitters, no conflicts P:4 U:1
• Conservation: PhyloP100: 4.04

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 2-178595585-G-A is Pathogenic according to our data. Variant chr2-178595585-G-A is described in ClinVar as [Likely_pathogenic]. Clinvar id is 202392.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.57769C>T	p.Arg19257Ter	stop_gained	295/363	ENST00000589042.5	NP_001254479.2
TTN-AS1	NR_038272.1	n.3365-2011G>A		intron_variant, non_coding_transcript_variant

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
TTN	ENST00000589042.5	c.57769C>T	p.Arg19257Ter	stop_gained	295/363	5	NM_001267550.2	ENSP00000467141	P1
TTN-AS1	ENST00000659121.1	n.417-2011G>A		intron_variant, non_coding_transcript_variant

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD3 exomes AF: 0.00000501 AC: 1 AN: 199640 Hom.: 0 AF XY: 0.00 AC XY: 0 AN XY: 106804

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: 0.0000117

Gnomad OTH exome AF: 0.00

GnomAD4 exome AF: 0.00000350 AC: 5 AN: 1429394 Hom.: 0 Cov.: 34 AF XY: 0.00000283 AC XY: 2 AN XY: 707834

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: 0.00000274

Gnomad4 OTH exome AF: 0.0000338

GnomAD4 genome Cov.: 32

Alfa AF: 0.0000468 Hom.: 0

ClinVar

Significance: Pathogenic/Likely pathogenic

Submissions summary: Pathogenic:4 Uncertain:1

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

not provided Pathogenic:2

Likely pathogenic, criteria provided, single submitter	clinical testing	Blueprint Genetics	Jun 01, 2018	- -
Pathogenic, criteria provided, single submitter	clinical testing	GeneDx	Nov 18, 2022	Identified in a patient with LVNC in the published literature (Miszalski-Jamka et al., 2017) and in a patient with DCM referred for genetic testing at GeneDx and segregated with disease in an affected family member; Not observed at significant frequency in large population cohorts (gnomAD); Nonsense 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: 34350506, 22335739, 28798025) -

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

Pathogenic, criteria provided, single submitter

clinical testing

Labcorp Genetics (formerly Invitae), Labcorp

Sep 21, 2023

This sequence change creates a premature translational stop signal (p.Arg19257*) in the TTN gene. While this is not anticipated to result in nonsense mediated decay, it is expected to create a truncated TTN protein. The frequency data for this variant in the population databases is considered unreliable, as metrics indicate poor data quality at this position in the gnomAD database. For these reasons, this variant has been classified as 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: 202392). This premature translational stop signal has been observed in individuals with dilated cardiomyopathy and/or left ventricular noncompaction (PMID: 28798025, 34350506; Invitae). -

Cardiovascular phenotype Pathogenic:1

Likely pathogenic, criteria provided, single submitter

clinical testing

Ambry Genetics

Sep 22, 2015

The p.R10192* variant (also known as c.30574C>T), located in coding exon 122 of the TTN gene, results from a C to T substitution at nucleotide position 30574. This changes the amino acid from an arginine to a stop codon within coding exon 122, and is located in the A-band region of the titin protein. Truncating alterations in TTN were observed at a significantly higher frequency among patients with dilated cardiomyopathy (DCM), or 54/203 (27%), compared to patients with hypertrophic cardiomyopathy (3 of 231, 1%, P=3x10-16) and healthy controls (7 of 249, 3%, P=9x10-14). Among families with multiple relatives with DCM, studies also provided strong data demonstrating segregation of TTN truncations with disease (Herman DS et al. N Engl J Med. 2012;366(7):619-28; Pugh TJ et al. Genet Med. 2014;16(8):601-8). The functional mechanism of TTN truncations leading to dilated cardiomyopathy is not well understood; however, truncating alterations are typically deleterious in nature (ACMG Standards and guidelines for the interpretation of sequence variants. Genet Med. 2015;17(5):405-24). As such, the p.R10192* variant is classified as likely pathogenic. -

not specified Uncertain:1

Uncertain significance, no assertion criteria provided

clinical testing

Stanford Center for Inherited Cardiovascular Disease, Stanford University

May 16, 2014

Note this variant was found in clinical genetic testing performed by one or more labs who may also submit to ClinVar. Thus any internal case data may overlap with the internal case data of other labs. The interpretation reviewed below is that of the Stanford Center for Inherited Cardiovascular Disease. p.Arg17616Stop (c.52846 C>T) in the TTN gene (NM_001256850.1) Given that 3% of controls have a vairant like this, the location of the variant within the gene, and the absence in controls, we consider it a variant of uncertain significance, probably disease causing. We do not recommend using this variant to assess risk in healthy relatives. We do recommend tesitng the affected father and any other affected relatives specifically for this variant to help clarify its role in disease. The variant is novel. I could find no online or published references. This substitution creates a premature stop codon. With >300 exons and >34,000 amino acids, TTN has the largest coding sequence in the genome, and the majority of the general population will have at least 1 rare (defined as a mean allele frequency <0.5%) missense or truncating variant at this locus. Truncating TTN variants have been shown by Herman et al. (2012) to be present in 27% of patients with familial dilated cardiomyopathy (DCM). Herman et al. report that they observed strong cosegregation (lod score 9.3) of nonsense and frameshift variants with clinical status among 60 members of 16 families affected by DCM, indicating an odds of approximately 1 in 10^9 that the segregation of these TTN variants occurred by chance. However, Herman et al (2012) also observed truncating TTN variants in approximately 3% of control individuals. In addition, Norton et al. (2013) showed that not all truncating variants in TTN segregate with disease (DCM) in affected families. Norton et al. identified 6 TTN truncating variants carried by individuals affected with DCM in 7 of 17 DCM families (logarithm of odds, 2.99); 2 of these 7 families also had novel missense variants that segregated with disease. Two additional novel truncating TTN variants did not segregate with DCM. Herman et al (2012) observed that TTN truncating variants found in subjects with DCM (as opposed to those found in subjects without the disease) were nonrandomly distributed within titin: they were overrepresented in the A-band region. Our patient's variant is located in the A-band region of titin. Thus, while the findings of Herman et al (2012) provide strong evidence that truncating TTN variants contribute to familial DCM, it is still challenging to determine the significance of anyone individual truncating variant. In total the variant has not been seen in ~6500 individuals from publicly available population datasets. The variant is not listed in the NHLBI Exome Sequencing Project dataset, which currently includes variant calls on ~6500 Caucasian and African American individuals (as of June 11th, 2014). There is a missense variant at this codon in 1 of 5968 individuals in ESP (p.Arg17616Gln). -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
BayesDel_addAF	Pathogenic	0.61	D
BayesDel_noAF	Pathogenic	0.63
CADD	Pathogenic	59
DANN	Uncertain	0.98
Eigen	Pathogenic	0.99
Eigen_PC	Pathogenic	0.83
FATHMM_MKL	Uncertain	0.94	D
MutationTaster	Benign	1.0	A;A;A;A;A;A
Vest4		0.95
GERP RS		5.1

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: rs794729275; hg19: chr2-179460312; COSMIC: COSV60246744; COSMIC: COSV60246744;