2-178535516-T-TA

Position:

• chr2-178535516-T-TA

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.101098_101099insT​(p.Asp33700ValfsTer13) variant causes a frameshift change involving the alteration of a conserved nucleotide. The variant allele was found at a frequency of 0.00000274 in 1,461,576 control chromosomes in the GnomAD database, with no homozygous occurrence. Variant has been reported in ClinVar as Likely pathogenic (★★). Synonymous variant affecting the same amino acid position (i.e. D33700D) has been classified as Likely benign. Variant results in nonsense mediated mRNA decay.

• Frequency:
  • Genomes: not found (cov: 33)
  • Exomes 𝑓: 0.0000027 (0 hom.)
• Consequence: TTN NM_001267550.2 frameshift
• Clinical Significance: Likely pathogenic criteria provided, multiple submitters, no conflicts P:3
• Conservation: PhyloP100: 7.91

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 2-178535516-T-TA is Pathogenic according to our data. Variant chr2-178535516-T-TA is described in ClinVar as [Likely_pathogenic]. Clinvar id is 223390.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.101098_101099insT	p.Asp33700ValfsTer13	frameshift_variant	358/363	ENST00000589042.5
TTN-AS1	NR_038272.1	n.220-216_220-215insA		intron_variant, non_coding_transcript_variant

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Appris	UniProt
TTN	ENST00000589042.5	c.101098_101099insT	p.Asp33700ValfsTer13	frameshift_variant	358/363	5	NM_001267550.2	P1
TTN-AS1	ENST00000659121.1	n.416+11880_416+11881insA		intron_variant, non_coding_transcript_variant

Frequencies

GnomAD3 genomes Cov.: 33

GnomAD4 exome AF: 0.00000274 AC: 4 AN: 1461576 Hom.: 0 Cov.: 38 AF XY: 0.00000275 AC XY: 2 AN XY: 727078

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: 0.00000360

Gnomad4 OTH exome AF: 0.00

GnomAD4 genome Cov.: 33

ClinVar

Significance: Likely pathogenic

Submissions summary: Pathogenic:3

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

Primary dilated cardiomyopathy Pathogenic:2

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. -
Likely pathogenic, criteria provided, single submitter	clinical testing	Laboratory for Molecular Medicine, Mass General Brigham Personalized Medicine	Apr 12, 2019	The p.Asp31132ValfsX13 variant in TTN has been reported in 1 individual with DCM (Roberts 2015) and was absent from large population studies. It has been reported in ClinVar (Variation ID #223390). This variant is predicted to cause a frameshift, which alters the protein’s amino acid sequence beginning at position 31132 and leads to a premature termination codon 13 amino acids downstream. This alteration is then predicted to lead to a truncated or absent protein. TTN truncating variants located in exons that are highly expressed in the heart are strongly associated with autosomal dominant DCM, particularly if they are located in the A-band (Herman 2012, Pugh 2014 , Roberts 2015). In addition, TTN variants have also been associated with myopathies and other neuromuscular conditions, which usually have autosomal recessive inheritance (Savarese 2016). The p.Asp31132ValfsX13 variant is located in a highly expressed exon in the M-band. In summary, although additional studies are required to fully establish its clinical significance, this variant meets criteria to be classified as likely pathogenic for TTN-associated diseases. ACMG/AMP Criteria applied: PVS1, PM2. -

Autosomal recessive limb-girdle muscular dystrophy type 2J Pathogenic:1

Likely pathogenic, criteria provided, single submitter

clinical testing

Labcorp Genetics (formerly Invitae), Labcorp

Aug 09, 2017

This sequence change results in a premature translational stop signal in the TTN gene (p.Asp33700Valfs*13). While this is not anticipated to result in nonsense mediated decay, it is expected to disrupt the last 2,292 amino acids of the TTN protein. This variant is not present in population databases (ExAC no frequency). This variant has not been reported in the literature in individuals with TTN-related disease. A different truncating  variant at this codon p.Asp33700Valfs*13 has been reported in the literature in an individual affected with dilated cardiomyopathy (DCM) (PMID: 25589632). However, truncating variants in the M-band have not been associated with DCM and the authors did not present any further evidence to confirm that this variant is causative of isolated DCM instead of an incidental finding. This variant is found in the M-band of this gene. While this particular variant has not been reported in the literature, truncating variants in the M-band of TTN previously reported in patients affected with various forms of myopathy and muscular dystrophy (PMID: 18948003, 23975875, 24395473). 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. -

Computational scores

Source: dbNSFP v4.3

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: rs869312122; hg19: chr2-179400243;