rs776970935

Positions:

• chr2-178630923-G-A

Variant summary

Our verdict is Pathogenic. Variant got 16 ACMG points: 16P and 0B. PVS1 PP5_Very_Strong

The NM_001267550.2(TTN):​c.44035C>T​(p.Arg14679Ter) variant causes a stop gained change involving the alteration of a conserved nucleotide. The variant allele was found at a frequency of 0.00000411 in 1,459,264 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: 0.0000041 (0 hom.)
• Consequence: TTN NM_001267550.2 stop_gained
• Clinical Significance: Likely pathogenic criteria provided, multiple submitters, no conflicts P:3
• Conservation: PhyloP100: 7.93

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 16 ACMG points.

• PVS1: Loss of function variant, product undergoes nonsense mediated mRNA decay. LoF is a known mechanism of disease.
• PP5: Variant 2-178630923-G-A is Pathogenic according to our data. Variant chr2-178630923-G-A is described in ClinVar as [Likely_pathogenic]. Clinvar id is 571684.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.44035C>T	p.Arg14679Ter	stop_gained	238/363	ENST00000589042.5

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Appris	UniProt
TTN	ENST00000589042.5	c.44035C>T	p.Arg14679Ter	stop_gained	238/363	5	NM_001267550.2	P1
TTN-AS1	ENST00000659121.1	n.502+33242G>A		intron_variant, non_coding_transcript_variant

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD3 exomes AF: 0.00000406 AC: 1 AN: 246250 Hom.: 0 AF XY: 0.00000748 AC XY: 1 AN XY: 133618

Gnomad AFR exome AF: 0.00

Gnomad AMR exome AF: 0.0000294

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: 0.00

Gnomad OTH exome AF: 0.00

GnomAD4 exome AF: 0.00000411 AC: 6 AN: 1459264 Hom.: 0 Cov.: 31 AF XY: 0.00000689 AC XY: 5 AN XY: 725890

Gnomad4 AFR exome AF: 0.00

Gnomad4 AMR exome AF: 0.0000226

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: 0.00000360

Gnomad4 OTH exome AF: 0.0000166

GnomAD4 genome Cov.: 32

ExAC AF: 0.00000828 AC: 1

ClinVar

Significance: 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

Likely pathogenic, criteria provided, single submitter

clinical testing

Invitae

Jan 08, 2024

This sequence change creates a premature translational stop signal (p.Arg14679*) 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. This premature translational stop signal has been observed in individual(s) with centronuclear myopathy (PMID: 33449170). This variant has been reported in individual(s) with dilated cardiomyopathy (Invitae); however, the role of the variant in this condition is currently unclear. This variant is also known as c.44260C>T. ClinVar contains an entry for this variant (Variation ID: 571684). 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, Invitae internal data). 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, Invitae internal data). 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. -

Cardiomyopathy Pathogenic:1

Likely pathogenic, criteria provided, single submitter

clinical testing

CHEO Genetics Diagnostic Laboratory, Children's Hospital of Eastern Ontario

Mar 29, 2023

- -

Cardiovascular phenotype Pathogenic:1

Likely pathogenic, criteria provided, single submitter

clinical testing

Ambry Genetics

Sep 21, 2021

The p.R5614* variant (also known as c.16840C>T), located in coding exon 65 of the TTN gene, results from a C to T substitution at nucleotide position 16840. This changes the amino acid from an arginine to a stop codon within coding exon 65. 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 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). As such, this alteration is classified as likely pathogenic. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
BayesDel_addAF	Pathogenic	0.62	D
BayesDel_noAF	Pathogenic	0.65
CADD	Pathogenic	55
DANN	Uncertain	0.99
Eigen	Pathogenic	1.3
Eigen_PC	Pathogenic	1.1
FATHMM_MKL	Pathogenic	0.98	D
MutationTaster	Benign	1.0	A;A;A;A;A;A
Vest4		0.95
GERP RS		6.2

Splicing

Name	Calibrated prediction	Score	Prediction
SpliceAI score (max)		0.12		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: rs776970935; hg19: chr2-179495650; COSMIC: COSV60365265; COSMIC: COSV60365265;