rs869312043

Positions:

• chr2-178636098-G-A

Variant summary

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

The NM_001267550.2(TTN):​c.41473C>T​(p.Arg13825Ter) variant causes a stop gained change involving the alteration of a non-conserved nucleotide. The variant allele was found at a frequency of 0.00000137 in 1,461,066 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: 32)
  • Exomes 𝑓: 0.0000014 (0 hom.)
• Consequence: TTN NM_001267550.2 stop_gained
• Clinical Significance: Conflicting classifications of pathogenicity criteria provided, conflicting classifications P:3 U:1
• Conservation: PhyloP100: 3.45

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 2-178636098-G-A is Pathogenic according to our data. Variant chr2-178636098-G-A is described in ClinVar as [Conflicting_classifications_of_pathogenicity]. Clinvar id is 223274.We mark this variant Likely_pathogenic, oryginal submissions are: {Likely_pathogenic=3, Uncertain_significance=1, Pathogenic=1}. Variant chr2-178636098-G-A is described in Lovd as [Likely_pathogenic].

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
TTN	NM_001267550.2	c.41473C>T	p.Arg13825Ter	stop_gained	226/363	ENST00000589042.5	NP_001254479.2

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
TTN	ENST00000589042.5	c.41473C>T	p.Arg13825Ter	stop_gained	226/363	5	NM_001267550.2	ENSP00000467141	P1
TTN-AS1	ENST00000659121.1	n.502+38417G>A		intron_variant, non_coding_transcript_variant

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD4 exome AF: 0.00000137 AC: 2 AN: 1461066 Hom.: 0 Cov.: 32 AF XY: 0.00000275 AC XY: 2 AN XY: 726812

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.: 32

ClinVar

Significance: Conflicting classifications of pathogenicity

Submissions summary: Pathogenic:3 Uncertain:1

Revision: criteria provided, conflicting classifications

Submissions by phenotype

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

Nov 27, 2023

This sequence change creates a premature translational stop signal (p.Arg13825*) 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 premature translational stop signal has been observed in individuals with clinical features of dilated cardiomyopathy (PMID: 25589632, 31251381, 31983221; Invitae). ClinVar contains an entry for this variant (Variation ID: 223274). This variant is located in the I band of TTN (PMID: 25589632). Truncating variants in this region have been reported in individuals affected with autosomal recessive centronuclear myopathy (PMID: 23975875). Truncating variants in this region have also been identified in individuals affected with autosomal dominant dilated cardiomyopathy and/or cardio-related conditions (PMID: 27869827, 32964742). For these reasons, this variant has been classified as Pathogenic. -

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 one individual 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

Likely pathogenic, criteria provided, single submitter

clinical testing

Ambry Genetics

Apr 07, 2020

The p.R4760* variant (also known as c.14278C>T), located in coding exon 53 of the TTN gene, results from a C to T substitution at nucleotide position 14278. This changes the amino acid from an arginine to a stop codon within coding exon 53. This alteration has been reported in association with dilated cardiomyopathy (DCM) (Roberts AM et al. Sci Transl Med, 2015 Jan;7:270ra6). This exon is located in the I-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 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). As such, this alteration is classified as likely pathogenic. -

not provided Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Eurofins Ntd Llc (ga)

Dec 08, 2016

- -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
BayesDel_addAF	Pathogenic	0.58	D
BayesDel_noAF	Pathogenic	0.60
CADD	Pathogenic	45
DANN	Benign	0.97
Eigen	Uncertain	0.59
Eigen_PC	Uncertain	0.32
FATHMM_MKL	Uncertain	0.87	D
MutationTaster	Benign	1.0	A;A;A;A;A;A
Vest4		0.93
GERP RS		0.36

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: rs869312043; hg19: chr2-179500825;