2-178717942-C-T

Variant names:

• chr2-178717942-C-T
• rs754247415
• NM_001267550.2:c.25063+1G>A

Variant summary

Our verdict is Uncertain significance. The variant received 5 ACMG points: 5P and 0B. PVS1_Moderate PM2 PP5

The NM_001267550.2(TTN):​c.25063+1G>A variant causes a splice donor, intron change. The variant allele was found at a frequency of 0.00000137 in 1,458,164 control chromosomes in the GnomAD database, with no homozygous occurrence. In-silico tool predicts a pathogenic outcome for this variant. 3/3 splice prediction tools predicting alterations to normal splicing. Variant has been reported in ClinVar as Conflicting classifications of pathogenicity (no stars).

• Frequency:
  • Genomes: not found (cov: 33)
  • Exomes 𝑓: 0.0000014 (0 hom.)
• Consequence: TTN NM_001267550.2 splice_donor, intron
• Scores: Splicing: ADA: 1.000
• Clinical Significance: Conflicting classifications of pathogenicity criteria provided, conflicting classifications P:2 U:1
• Conservation: PhyloP100: 6.53
• Publications: 0 publications found

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

Our verdict: Uncertain_significance. The variant received 5 ACMG points.

• PVS1: Splicing +-2 bp (donor or acceptor) variant, product NOT destroyed by NMD, known LOF gene, truncates exone, which is 0.0025839075 fraction of the gene. No cryptic splice site detected. Exon removal is inframe change.
• PM2: Very rare variant in population databases, with high coverage
• PP5: Variant 2-178717942-C-T is Pathogenic according to our data. Variant chr2-178717942-C-T is described in ClinVar as Conflicting_classifications_of_pathogenicity. ClinVar VariationId is 466942.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	MANE	Protein	UniProt
TTN	NM_001267550.2	c.25063+1G>A		splice_donor_variant, intron_variant	Intron 86 of 362	ENST00000589042.5	NP_001254479.2

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	TSL	MANE	Protein	Appris	UniProt
TTN	ENST00000589042.5	c.25063+1G>A		splice_donor_variant, intron_variant	Intron 86 of 362	5	NM_001267550.2	ENSP00000467141.1

Frequencies

GnomAD3 genomes Cov.: 33

GnomAD2 exomes AF: 0.00000404 AC: 1 AN: 247500 AF XY: 0.00

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 FIN exome AF: 0.00

Gnomad NFE exome AF: 0.00000893

Gnomad OTH exome AF: 0.00

GnomAD4 exome AF: 0.00000137 AC: 2 AN: 1458164 Hom.: 0 Cov.: 35 AF XY: 0.00000138 AC XY: 1 AN XY: 724722

African (AFR) AF: 0.00 AC: 0 AN: 33378

American (AMR) AF: 0.00 AC: 0 AN: 44602

Ashkenazi Jewish (ASJ) AF: 0.00 AC: 0 AN: 26042

East Asian (EAS) AF: 0.00 AC: 0 AN: 39624

South Asian (SAS) AF: 0.00 AC: 0 AN: 86042

European-Finnish (FIN) AF: 0.00 AC: 0 AN: 53342

Middle Eastern (MID) AF: 0.00 AC: 0 AN: 5750

European-Non Finnish (NFE) AF: 0.00000180 AC: 2 AN: 1109136

Other (OTH) AF: 0.00 AC: 0 AN: 60248

GnomAD4 genome Cov.: 33

Alfa AF: 0.0000282 Hom.: 0

Bravo AF: 0.00000378

ExAC AF: 0.00000827 AC: 1

ClinVar

Significance: Conflicting classifications of pathogenicity

Submissions summary: Pathogenic:2 Uncertain:1

Revision: criteria provided, conflicting classifications

Submissions by phenotype

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

-

Neuberg Centre For Genomic Medicine, NCGM

Significance: Likely pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

The splice donor variant c.25063+1G>A in TTN gene has been previously reported in compound heterozygous state in a 34-year old Belgian patient affected with muscle disorder (Savarese et al. 2018). This sequence change affects a donor splice site in intron 86 of the TTN gene. It is expected to disrupt RNA splicing and likely results in a disrupted protein product, but is not anticipated to result in nonsense mediated decay. The variant is novel (not in any individuals) in gnomAD Exomes and 1000 Genomes. This variant has been reported to the ClinVar database as Uncertain Significance. This variant is present in the ExAC population database with a frequency of 0.002%. Although this is a rare truncating variant, truncating variants have been shown to be highly prevalent in the TTN gene in the general population and unaffected individuals (Akinrinade et al. 2015). However, truncating mutations in this region have also been reported to cause recessive myotubular myopathy (Ceyhan-Birsoy et al. 2013). The nucleotide change in TTN is predicted as conserved by GERP++ and PhyloP across 100 vertebrates. For these reasons, this variant has been classified as Likely Pathogenic -

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

Aug 12, 2024

Labcorp Genetics (formerly Invitae), Labcorp

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

This sequence change affects a donor splice site in intron 86 of the TTN gene. It is expected to disrupt RNA splicing and likely results in a truncated or disrupted TTN protein. This variant is not present in population databases (gnomAD no frequency). Disruption of this splice site has been observed in individuals with clinical features of autosomal recessive centronuclear myopathy (PMID: 29435569, 32815318). ClinVar contains an entry for this variant (Variation ID: 466942). Algorithms developed to predict the effect of sequence changes on RNA splicing suggest that this variant may disrupt the consensus splice site. 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). For these reasons, this variant has been classified as Pathogenic. -

not provided Uncertain:1

Dec 30, 2016

Eurofins Ntd Llc (ga)

Significance: Uncertain significance

Review Status: criteria provided, single submitter

Collection Method: clinical testing

- -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
BayesDel_addAF	Pathogenic	0.40	D
BayesDel_noAF	Pathogenic	0.34
CADD	Pathogenic	32
DANN	Uncertain	0.99
Eigen	Pathogenic	1.2
Eigen_PC	Pathogenic	1.1
FATHMM_MKL	Pathogenic	0.99	D
PhyloP100		6.5
GERP RS		6.2
Mutation Taster		=0/100	disease causing

Splicing

Name	Calibrated prediction	Score	Prediction
dbscSNV1_ADA	Pathogenic	1.0
dbscSNV1_RF	Pathogenic	0.94
SpliceAI score (max)		0.84		Details are displayed if max score is > 0.2
DS_DL_spliceai		0.84		Position offset: 1

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

Other links and lift over

dbSNP: rs754247415; hg19: chr2-179582669;