rs778172350

Positions:

• chr2-178756292-T-TC

Variant summary

Our verdict is Likely pathogenic. Variant got 8 ACMG points: 8P and 0B. PVS1

The NM_001267550.2(TTN):​c.11183_11184insG​(p.Leu3729ThrfsTer9) variant causes a frameshift change. The variant allele was found at a frequency of 0.000304 in 1,613,856 control chromosomes in the GnomAD database, with no homozygous occurrence. Variant has been reported in ClinVar as Uncertain significance (★★). Variant results in nonsense mediated mRNA decay.

• Frequency:
  • Genomes: 𝑓 0.00016 (0 hom., cov: 32)
  • Exomes 𝑓: 0.00032 (0 hom.)
• Consequence: TTN NM_001267550.2 frameshift
• Clinical Significance: Uncertain significance criteria provided, multiple submitters, no conflicts U:7
• Conservation: PhyloP100: 4.61

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 Likely_pathogenic. Variant got 8 ACMG points.

• PVS1: Loss of function variant, product undergoes nonsense mediated mRNA decay. LoF is a known mechanism of disease.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
TTN	NM_001267550.2	c.11183_11184insG	p.Leu3729ThrfsTer9	frameshift_variant	46/363	ENST00000589042.5	NP_001254479.2
TTN	NM_133379.5	c.10303+2691_10303+2692insG		intron_variant		ENST00000360870.10	NP_596870.2

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
TTN	ENST00000589042.5	c.11183_11184insG	p.Leu3729ThrfsTer9	frameshift_variant	46/363	5	NM_001267550.2	ENSP00000467141	P1
TTN	ENST00000360870.10	c.10303+2691_10303+2692insG		intron_variant		5	NM_133379.5	ENSP00000354117
TTN-AS1	ENST00000659121.1	n.1252dup		non_coding_transcript_exon_variant	7/13

Frequencies

GnomAD3 genomes AF: 0.000164 AC: 25 AN: 152228 Hom.: 0 Cov.: 32

Gnomad AFR AF: 0.0000723

Gnomad AMI AF: 0.00

Gnomad AMR AF: 0.00

Gnomad ASJ AF: 0.00

Gnomad EAS AF: 0.00

Gnomad SAS AF: 0.00

Gnomad FIN AF: 0.00

Gnomad MID AF: 0.00

Gnomad NFE AF: 0.000323

Gnomad OTH AF: 0.00

GnomAD3 exomes AF: 0.000105 AC: 26 AN: 248776 Hom.: 0 AF XY: 0.0000815 AC XY: 11 AN XY: 134932

Gnomad AFR exome AF: 0.0000646

Gnomad AMR exome AF: 0.0000290

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: 0.000186

Gnomad OTH exome AF: 0.000497

GnomAD4 exome AF: 0.000318 AC: 465 AN: 1461510 Hom.: 0 Cov.: 33 AF XY: 0.000283 AC XY: 206 AN XY: 727048

Gnomad4 AFR exome AF: 0.0000299

Gnomad4 AMR exome AF: 0.0000447

Gnomad4 ASJ exome AF: 0.0000383

Gnomad4 EAS exome AF: 0.00

Gnomad4 SAS exome AF: 0.00

Gnomad4 FIN exome AF: 0.00

Gnomad4 NFE exome AF: 0.000404

Gnomad4 OTH exome AF: 0.000199

GnomAD4 genome AF: 0.000164 AC: 25 AN: 152346 Hom.: 0 Cov.: 32 AF XY: 0.0000940 AC XY: 7 AN XY: 74488

Gnomad4 AFR AF: 0.0000721

Gnomad4 AMR AF: 0.00

Gnomad4 ASJ AF: 0.00

Gnomad4 EAS AF: 0.00

Gnomad4 SAS AF: 0.00

Gnomad4 FIN AF: 0.00

Gnomad4 NFE AF: 0.000323

Gnomad4 OTH AF: 0.00

Alfa AF: 0.000396 Hom.: 0

Bravo AF: 0.000185

EpiCase AF: 0.000436

EpiControl AF: 0.0000593

ClinVar

Significance: Uncertain significance

Submissions summary: Uncertain:7

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

not provided Uncertain:3

Uncertain significance, criteria provided, single submitter	clinical testing	CeGaT Center for Human Genetics Tuebingen	Oct 01, 2023	TTN: PVS1:Moderate, PS4:Supporting -
Uncertain significance, criteria provided, single submitter	clinical testing	GeneDx	Feb 17, 2014	c.10670dupG: p.Leu3558ThrfsX9 (L3558TfsX9) in exon 44 of the TTN gene (#NM_133437.3). The normal sequence with the base that is duplicated in braces is: CAAG{G}ACTA. The c.10670dupG variant has not been reported as a disease-causing mutation or as a benign polymorphism to our knowledge. This variant causes a shift in reading frame starting at codon Leucine 3558, changing it to a Threonine, and creating a premature stop codon at position 9 of the new reading frame, denoted p.Leu3558ThrfsX9. This variant is expected to result in either an abnormal, truncated protein product or loss of protein from this allele through nonsense-mediated mRNA decay. However, c.10670dupG is located in an alternate transcript of the TTN gene where no disease-causing mutations have been reported.With the clinical and molecular information available at this time, we cannot definitively determine if c.10670dupG is a disease-causing mutation or a rare benign variant. The variant is found in DCM-CRDM panel(s). -
Uncertain significance, criteria provided, single submitter	research	Biesecker Lab/Clinical Genomics Section, National Institutes of Health	Jun 24, 2013	- -

Primary dilated cardiomyopathy Uncertain:2

Uncertain significance, 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 with low levels of cardiac expression. 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. -
Uncertain significance, 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 with low levels of cardiac expression. 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. -

not specified Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Women's Health and Genetics/Laboratory Corporation of America, LabCorp

Mar 24, 2022

Variant summary: TTN NM_133378.4: c.10303+2691dupG alters a concerved nucleotide located at a position not widely known to affect splicing. 4/4 computational tools predict no significant impact on normal splicing. However, these predictions have yet to be confirmed by functional studies. This variant is also annotated as NM_001267550.1: c.11183dupG (p.Leu3729fs) in exon 46 of meta transcript. This exon is considered as a low expression exon with a percentage spliced in (PSI) score of 4% and is therefore not considered as a constitutively expressed exon of critical relevance to TTN function. TTN truncating variants in this exon are considered to be tolerated and therefore not relevant to any of the penetrant TTN-related disorder phenotypes. The variant allele was found at a frequency of 0.0001 in 248776 control chromosomes. This frequency is not significantly higher than estimated for a pathogenic variant in TTN causing Cardiomyopathy (0.0001 vs 0.00063), allowing no conclusion about variant significance. c.10303+2691dupG has been reported as c.11183dupG in the literature in a variety of settings such as, controls and individuals with heart failure from the UK biobank cohort (example, Choi_2020), one Dilated Cardiomyopathy (DCM) proband from a cohort that underwent reverse-parent offspring analysis (example, Jansen_2019), in one individual from a cohort of patients with early-onset artial fibrillation (example, Yoneda_2021). These report(s) do not provide unequivocal conclusions about association of the variant with penetrant TTN-related phenotypes of Dilated Cardiomyopathy/Limb-Girdle Muscular Dystrophy, Type 2J. At-least one co-occurrence with another pathogenic variant(s) has been reported in an individual from a cohort with early-onset Atrial Fibrillation (AF diagnosed before the age of 66 years)(Yoneda_2021, MYH7 c.1988G>A, p.Arg663His), although the specific clinical details were not reported. This provides supporting evidence for a benign role. To our knowledge, no experimental evidence demonstrating an impact on protein function has been reported. Two clinical diagnostic laboratories have submitted clinical-significance assessments for this variant to ClinVar after 2014 without evidence for independent evaluation. One laboratory classified the variant as likely pathogenic and one laboratory classified the variant as uncertain significance. Based on the evidence outlined above, the variant was classified as VUS-possibly benign. -

Cardiomyopathy Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

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

Jun 26, 2017

- -

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: rs778172350; hg19: chr2-179621019;