rs876658058

Positions:

chr2-178640539-AC-A

Variant summary

Our verdict is Uncertain significance. Variant got 2 ACMG points: 2P and 0B. PVS1_Moderate

The NM_001267550.2(TTN):c.40723+1del variant causes a splice donor change involving the alteration of a non-conserved nucleotide. The variant allele was found at a frequency of 0.00000687 in 1,602,320 control chromosomes in the GnomAD database, with no homozygous occurrence. 1/1 splice prediction tools predicting alterations to normal splicing. Variant has been reported in ClinVar as Conflicting classifications of pathogenicity (no stars).

Frequency

Genomes: 𝑓 0.0000066 ( 0 hom., cov: 32)

Exomes 𝑓: 0.0000069 ( 0 hom. )

Consequence

TTN
NM_001267550.2 splice_donor

Scores

Not classified

Clinical Significance

Conflicting classifications of pathogenicity criteria provided, conflicting classifications P:1U:4

Conservation

PhyloP100: 2.71

Variant links:

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 links:

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]

TTN-AS1 links:

Genome browser will be placed here

ACMG classification

Classification made for transcript

Verdict is Uncertain_significance. Variant got 2 ACMG points.

PVS1

Splicing +-2 bp (donor or acceptor) variant, product NOT destroyed by NMD, known LOF gene, truncates exone, which is 8.2425727E-4 fraction of the gene. No cryptic splice site detected. Exon removal is inframe change.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
TTN	NM_001267550.2 linkuse as main transcript	c.40723+1del		splice_donor_variant		ENST00000589042.5	NP_001254479.2

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
TTN	ENST00000589042.5 linkuse as main transcript	c.40723+1del		splice_donor_variant		5	NM_001267550.2	ENSP00000467141	P1
TTN-AS1	ENST00000659121.1 linkuse as main transcript	n.502+42860del		intron_variant, non_coding_transcript_variant

Frequencies

GnomAD3 genomes

AF:

0.00000658

AC:

AN:

151914

Hom.:

Cov.:

show subpopulations

Gnomad AFR

AF:

0.00

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:

0.0000147

Gnomad OTH

AF:

0.00

GnomAD3 exomes

AF:

0.00000417

AC:

AN:

239726

Hom.:

AF XY:

0.00

AC XY:

AN XY:

130240

show subpopulations

Gnomad AFR exome

AF:

0.00

Gnomad AMR exome

AF:

0.00

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:

0.00000910

Gnomad OTH exome

AF:

0.00

GnomAD4 exome

AF:

0.00000689

AC:

AN:

1450406

Hom.:

Cov.:

AF XY:

0.00000693

AC XY:

AN XY:

721566

show subpopulations

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:

0.00000903

Gnomad4 OTH exome

AF:

0.00

GnomAD4 genome

AF:

0.00000658

AC:

AN:

151914

Hom.:

Cov.:

AF XY:

0.00

AC XY:

AN XY:

74170

show subpopulations

Gnomad4 AFR

AF:

0.00

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:

0.0000147

Gnomad4 OTH

AF:

0.00

Bravo

AF:

0.00000378

ClinVar

Significance: Conflicting classifications of pathogenicity

Submissions summary: Pathogenic:1Uncertain:4

Revision: criteria provided, conflicting classifications

LINK: link

Submissions by phenotype

TTN-related disorder

Pathogenic:1

Likely pathogenic, criteria provided, single submitter

clinical testing

PreventionGenetics, part of Exact Sciences

Mar 09, 2023

The TTN c.40723+1delG variant is predicted to result in a deletion affecting a canonical splice site. To our knowledge, this variant has not been reported in the literature. This variant is located in the TTN protein I-band region. RNA sequencing studies from heart tissue indicate this exon is commonly included in TTN mRNA transcripts (Exon 221, PSI of 95%-100%, Roberts et al. 2015. PubMed ID: 25589632; https://cardiodb.org/titin/titin_transcripts.php). TTN truncating variants are reported in 1-2% of presumably healthy individuals, but occur more frequently in exons with low PSI values (Roberts et al. 2015. PMID: 25589632; Herman et al. 2012. PMID: 22335739). However, many cases of recessive TTN-related myopathies in which the individual is compound heterozygous for two loss of function variants in TTN have also been reported (See Ceyhan-Birsoy et al. 2013. PMID: 23975875; Chauveau et al. 2014. PubMed ID: 24105469; Evilä et al. 2016. PubMed ID: 27796757; Ge et al. 2019. PubMed ID: 31053406). This variant is reported in 1 of ~240,000 alleles in individuals of European (Non-Finnish) descent in gnomAD (http://gnomad.broadinstitute.org/variant/2-179505266-AC-A). This variant is interpreted as likely pathogenic for both autosomal recessive and dominant TTN-related disorders. -

not specified

Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Laboratory for Molecular Medicine, Mass General Brigham Personalized Medicine

Jan 13, 2016

Variant classified as Uncertain Significance - Favor Pathogenic. The c.33109+1de l variant in TTN has not been previously reported in individuals with cardiomyop athy or in large population studies. This variant occurs in the invariant region (+/- 1,2) of the splice consensus sequence and is predicted to cause altered sp licing leading to an abnormal or absent protein. Truncating variants in TTN are strongly associated with DCM if they are located in an exon that is highly expre ssed in the heart (Roberts 2015) and splice variants often lead to truncation. T he c.33109+1del variant is located in the highly expressed exon 170 of the I-ban d. While there is some suspicion for a pathogenic role, its significance remain s uncertain due to the lack of certainty on whether it leads to truncation combi ned with the architecture of this part of the TTN protein (multiple repeated sub -domains). -

Autosomal recessive limb-girdle muscular dystrophy type 2J;C1858763:Dilated cardiomyopathy 1G

Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Labcorp Genetics (formerly Invitae), Labcorp

Mar 09, 2023

This variant is located in the I band of TTN (PMID: 25589632). Truncating variants in this region have been shown to be highly prevalent in the general population and unaffected individuals (PMID: 26701604, 22335739). However, truncating variants in this region have also been reported in individuals affected with autosomal recessive centronuclear myopathy (PMID: 23975875). In summary, the available evidence is currently insufficient to determine the role of this variant in disease. Therefore, it has been classified as a Variant of Uncertain Significance. Algorithms developed to predict the effect of sequence changes on RNA splicing suggest that this variant may disrupt the consensus splice site. ClinVar contains an entry for this variant (Variation ID: 229431). This variant has not been reported in the literature in individuals affected with TTN-related conditions. This variant is present in population databases (no rsID available, gnomAD 0.0009%). This sequence change affects a splice site in intron 221 of the TTN gene. It is expected to disrupt RNA splicing and likely results in a truncated or disrupted TTN protein. -

not provided

Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

GeneDx

Aug 24, 2023

Has not been previously published as pathogenic or benign to our knowledge; Not observed at a significant frequency in large population cohorts (gnomAD); Canonical splice site variant expected to result in aberrant splicing, although in the absence of functional evidence the actual effect of this sequence change is unknown; Located in a region of TTN within the I-band in which the majority of loss of function variants are significantly associated with autosomal dominant titinopathies (Deo et al., 2016; Schafer et al., 2017); This variant is associated with the following publications: (PMID: 27535533, 26582918, 27625338, 27869827) -

Cardiovascular phenotype

Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Ambry Genetics

Jul 18, 2023

The c.13528+1delG intronic variant, located in intron 48 of the TTN gene, results from a deletion of one nucleotide within intron 48 of the TTN gene. Exon 48 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 disrupts the canonical splice site and is expected to cause aberrant splicing. In silico splice site analysis predicts that this alteration will weaken the native splice donor site and will result in the creation or strengthening of a novel splice donor site. However, although direct evidence is unavailable, this alteration is predicted to result in an in-frame transcript that is not expected to trigger nonsense-mediated mRNA decay. The exact functional effect of the predicted splice impact is unknown. This nucleotide position is highly conserved in available vertebrate species. Since supporting evidence is limited at this time, the clinical significance of this alteration remains unclear. -

Computational scores

Source: dbNSFP v4.3

Name

Calibrated prediction

Score

Prediction

Splicing

Name

Calibrated prediction

Score

Prediction

SpliceAI score (max)

1.0

Details are displayed if max score is > 0.2

DS_DG_spliceai

0.52

Position offset: 3

DS_DL_spliceai

1.0

Position offset: 2

Find out detailed SpliceAI scores and Pangolin per-transcript scores at spliceailookup.broadinstitute.org

Publications

LitVar

Below is the list of publications found by LitVar. It may be empty.

Variant summary

Frequency

Consequence

Scores

Clinical Significance

Conservation

ACMG classification

Transcripts

RefSeq

Ensembl

Frequencies

ClinVar

Submissions by phenotype

Computational scores

Splicing

Publications

LitVar

Other links and lift over