rs1553682168

Positions:

• chr2-178605110-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.54067C>T​(p.Arg18023Ter) variant causes a stop gained change involving the alteration of a non-conserved nucleotide. The variant allele was found at a frequency of 0.00000205 in 1,460,644 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: 0.0000021 (0 hom.)
• Consequence: TTN NM_001267550.2 stop_gained
• Clinical Significance: Pathogenic/Likely pathogenic criteria provided, multiple submitters, no conflicts P:3
• Conservation: PhyloP100: 2.58

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 2-178605110-G-A is Pathogenic according to our data. Variant chr2-178605110-G-A is described in ClinVar as [Likely_pathogenic]. Clinvar id is 466638.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.54067C>T	p.Arg18023Ter	stop_gained	280/363	ENST00000589042.5	NP_001254479.2
TTN-AS1	NR_038272.1	n.4297G>A		non_coding_transcript_exon_variant	17/17

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
TTN	ENST00000589042.5	c.54067C>T	p.Arg18023Ter	stop_gained	280/363	5	NM_001267550.2	ENSP00000467141	P1
TTN-AS1	ENST00000659121.1	n.502+7429G>A		intron_variant, non_coding_transcript_variant

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD4 exome AF: 0.00000205 AC: 3 AN: 1460644 Hom.: 0 Cov.: 32 AF XY: 0.00000138 AC XY: 1 AN XY: 726636

Gnomad4 AFR exome AF: 0.00

Gnomad4 AMR exome AF: 0.00

Gnomad4 ASJ exome AF: 0.00

Gnomad4 EAS exome AF: 0.0000253

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: Pathogenic/Likely pathogenic

Submissions summary: Pathogenic:3

Revision: criteria provided, multiple submitters, no conflicts

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

Jul 27, 2023

This premature translational stop signal has been observed in individuals with clinical features of myopathy and dilated cardiomyopathy (PMID: 29382405; Invitae). ClinVar contains an entry for this variant (Variation ID: 466638). 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). For these reasons, this variant has been classified as Pathogenic. This variant is not present in population databases (gnomAD no frequency). This sequence change creates a premature translational stop signal (p.Arg18023*) in the TTN gene. While this is not anticipated to result in nonsense mediated decay, it is expected to create a truncated TTN protein. -

not provided Pathogenic:1

Likely pathogenic, criteria provided, single submitter

clinical testing

GeneDx

Aug 14, 2024

Reported as c.46363C>T (p.Arg15455Ter) in a patient with teenage-onset myalgias, recurrent rhabdomyolysis, progressive proximal weakness, atrial fibrillation, and congestive heart failure who harbors an additional pathogenic TTN splice site variant (PMID: 29382405); Located in the A-band region of TTN in which the majority of loss of function variants have been associated with autosomal dominant titinopathies (PMID: 22335739); 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; This variant is associated with the following publications: (PMID: 31589614, 22335739, 36264615, 29382405) -

Cardiovascular phenotype Pathogenic:1

Likely pathogenic, criteria provided, single submitter

clinical testing

Ambry Genetics

Sep 10, 2020

The p.R8958* variant (also known as c.26872C>T), located in coding exon 107 of the TTN gene, results from a C to T substitution at nucleotide position 26872. This changes the amino acid from an arginine to a stop codon within coding exon 107. 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 (referred to as p.Arg15455Ter, c.4636C>T) co-occurred with a TTN canonical splice site alteration in an individual with muscle weakness, myalgias, atrial fibrillation, and heart failure (Wu L et al. Can J Neurol Sci, 2018 05;45:262-268). 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. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
BayesDel_addAF	Pathogenic	0.58	D
BayesDel_noAF	Pathogenic	0.60
CADD	Pathogenic	59
DANN	Uncertain	0.99
Eigen	Pathogenic	1.0
Eigen_PC	Pathogenic	0.89
FATHMM_MKL	Uncertain	0.92	D
MutationTaster	Benign	1.0	A;A;A;A;A;A
Vest4		0.89
GERP RS		4.8

Splicing

Name	Calibrated prediction	Score	Prediction
SpliceAI score (max)		0.010		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: rs1553682168; hg19: chr2-179469837; COSMIC: COSV59902742; COSMIC: COSV59902742;