rs794729382

chr2-178570804-G-Achr2-178570804-G-T

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.75328C>T(p.Arg25110Ter) variant causes a stop gained change involving the alteration of a non-conserved nucleotide. The variant allele was found at a frequency of 0.00000342 in 1,461,352 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: 0.0000034 (0 hom.)
• Consequence: TTN NM_001267550.2 stop_gained
• Clinical Significance: Pathogenic/Likely pathogenic criteria provided, multiple submitters, no conflicts P:5
• Conservation: PhyloP100: 2.87

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 2-178570804-G-A is Pathogenic according to our data. Variant chr2-178570804-G-A is described in ClinVar as [Likely_pathogenic]. Clinvar id is 202521.Status of the report is criteria_provided_multiple_submitters_no_conflicts, 2 stars.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	UniProt
TTN	NM_001267550.2	c.75328C>T	p.Arg25110Ter	stop_gained	326/363	ENST00000589042.5
TTN-AS1	NR_038272.1	n.2044-11768G>A		intron_variant, non_coding_transcript_variant

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Appris	UniProt
TTN	ENST00000589042.5	c.75328C>T	p.Arg25110Ter	stop_gained	326/363	5	NM_001267550.2	P1
TTN-AS1	ENST00000659121.1	n.417-26792G>A		intron_variant, non_coding_transcript_variant

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD4 exome AF: 0.00000342 AC: 5 AN: 1461352 Hom.: 0 Cov.: 40 AF XY: 0.00000413 AC XY: 3 AN XY: 726974

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: 0.00000270

Gnomad4 OTH exome AF: 0.0000331

GnomAD4 genome Cov.: 32

Alfa AF: 0.0000712 Hom.: 0

Bravo AF: 0.00000756

ClinVar

Significance: Pathogenic/Likely pathogenic

Submissions summary: Pathogenic:5

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

not provided Pathogenic:2

Pathogenic, criteria provided, single submitter	clinical testing	GeneDx	Jun 07, 2023	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 TTN in which the majority of loss of function variants have been associated with autosomal dominant titinopathies (Herman et al., 2012); Not observed in large population cohorts (gnomAD); Has not been previously published as pathogenic or benign to our knowledge; This variant is associated with the following publications: (PMID: 22335739, 35177841, 33432171) -
Likely pathogenic, no assertion criteria provided	provider interpretation	Stanford Center for Inherited Cardiovascular Disease, Stanford University	Sep 11, 2017	Given that this is a rare, truncating variant in the A-band of TTN, we consider this variant likely pathogenic and we do feel it is suitable for assessing risk in healthy relatives ("predictive genetic testing"). Gene-level evidence: TTN encodes titin (also known as connectin), the largest protein in humans; titin plays a critical role in the elastic properties of the sarcomere. Two titin molecules span the sarcomere, anchored at the Z-line and M-line. TTN variants are the most common cause of idiopathic dilated cardiomyopathy. Variant type: Truncating variant in the A-band. TTN truncating variants are seen in 13-30% of people with DCM and are thought to confer pathogenesis in a dominant-negative fashion (Herman et al 2012, Roberts et al 2015). There is strong evidence implicating them in the pathogenesis of DCM, though it remains unclear whether they are confer risk in a Mendelian or multifactorial fashion (Watkins et al 2015). Furthermore, each individual TTN variant must be evaluated carefully for potential pathogenicity given the presence of truncating TTN variants in 1-3% of the general population (Herman et al 2012, Roberts et al 2015) and the failure of some TTN truncating variants to segregate in DCM families (Norton et al 2013). TTN truncating variants located in the A-band and in exons frequently included in the cardiac isoforms N2B and N2BA are enriched in DCM patients versus controls (Roberts et al 2015). However, it is notable that when focusing these variants (A-band, frequently included N2B, N2BA), 15% of DCM cases and 1% of a normal sample have such variants (Roberts et al 2015). Roberts et al (2015) estimated that when such a variant is found in a proband there is a 93% chance it is disease-causing. Review of the p.Arg25510* truncating variant in cardiodb.org: The genomic coordinates for this variant are chr2: 179435531 (hg19). Per the TTN tool at cardiodb.org, LRG exon number is 326 (this is a meta exon number system created to include all TTN exons and preferred in reporting variants), N2BA transcript is 276. It is located in the A-band and is 100% spliced in to cardiac isoforms. Another variant in the same exon has previously been reported in more than 50 cases of DCM. Total number of cases (not including our patient): at least 1: -ClinVar: present -Classified as: likely pathogenic -Number of individuals: unknown -Submitted by: GeneDx -Last reviewed: March 2017 -Case data: There is no published literature available to review. Prevalence in the general population: Per varsome.com it is not present in gnomAD, which has >140,000 samples. Median coverage in exome samples is 93.9x and in genome samples is 34.3x. -

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

Likely pathogenic, criteria provided, single submitter

clinical testing

Invitae

Jan 21, 2024

This sequence change creates a premature translational stop signal (p.Arg25110*) 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: 202521). 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. -

Autosomal recessive limb-girdle muscular dystrophy type 2J;C1838244:Tibial muscular dystrophy;C1858763:Dilated cardiomyopathy 1G;C1861065:Hypertrophic cardiomyopathy 9;C1863599:Myopathy, myofibrillar, 9, with early respiratory failure;C2673677:Early-onset myopathy with fatal cardiomyopathy Pathogenic:1

Likely pathogenic, criteria provided, single submitter

clinical testing

Fulgent Genetics, Fulgent Genetics

Nov 18, 2021

- -

Cardiovascular phenotype Pathogenic:1

Likely pathogenic, criteria provided, single submitter

clinical testing

Ambry Genetics

Oct 07, 2022

The p.R16045* variant (also known as c.48133C>T), located in coding exon 153 of the TTN gene, results from a C to T substitution at nucleotide position 48133. 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 Jan;49:46-53). As such, this alteration is classified as likely pathogenic. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
BayesDel_addAF	Pathogenic	0.38	D
BayesDel_noAF	Pathogenic	0.32
Cadd	Pathogenic	64
Dann	Benign	0.97
Eigen	Pathogenic	0.79
Eigen_PC	Uncertain	0.58
FATHMM_MKL	Uncertain	0.93	D
MutationTaster	Benign	1.0	A;A;A;A;A;A
Vest4		0.97
GERP RS		3.8

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: rs794729382; hg19: chr2-179435531; COSMIC: COSV60013361;