chr2-178595506-C-T

Variant names:

• chr2-178595506-C-T
• rs397517631
• NM_001267550.2:c.57847+1G>A

Variant summary

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

The NM_001267550.2(TTN):​c.57847+1G>A variant causes a splice donor, intron change involving the alteration of a conserved nucleotide. 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 Uncertain significance (★★).

• Frequency:
  • Genomes: 𝑓 0.000027 (0 hom., cov: 32)
  • Exomes 𝑓: 0.000099 (0 hom.)
  • Failed GnomAD Quality Control
• Consequence: TTN NM_001267550.2 splice_donor, intron
• Scores: Splicing: ADA: 1.000
• Clinical Significance: Uncertain significance criteria provided, multiple submitters, no conflicts U:3
• Conservation: PhyloP100: 7.86

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 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 0.0028061792 fraction of the gene. No cryptic splice site detected. Exon removal is inframe change.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	MANE	Protein	UniProt
TTN	NM_001267550.2	c.57847+1G>A		splice_donor_variant, intron_variant	Intron 295 of 362	ENST00000589042.5	NP_001254479.2

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	TSL	MANE	Protein	Appris	UniProt
TTN	ENST00000589042.5	c.57847+1G>A		splice_donor_variant, intron_variant	Intron 295 of 362	5	NM_001267550.2	ENSP00000467141.1

Frequencies

GnomAD3 genomes AF: 0.00 AC: 4 AN: 150038 Hom.: 0 Cov.: 32 FAILED QC

Gnomad AFR AF: 0.0000245

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: 0.000302

Gnomad MID AF: 0.00

Gnomad NFE AF: 0.00

Gnomad OTH AF: 0.00

GnomAD4 exome Data not reliable, filtered out with message: AS_VQSR AF: 0.0000988 AC: 137 AN: 1386722 Hom.: 0 Cov.: 34 AF XY: 0.000101 AC XY: 69 AN XY: 683722

Gnomad4 AFR exome AF: 0.000196

Gnomad4 AMR exome AF: 0.00228

Gnomad4 ASJ exome AF: 0.0000401

Gnomad4 EAS exome AF: 0.00

Gnomad4 SAS exome AF: 0.000158

Gnomad4 FIN exome AF: 0.00

Gnomad4 NFE exome AF: 0.0000372

Gnomad4 OTH exome AF: 0.0000522

GnomAD4 genome Data not reliable, filtered out with message: AS_VQSR AF: 0.0000267 AC: 4 AN: 150038 Hom.: 0 Cov.: 32 AF XY: 0.0000274 AC XY: 2 AN XY: 73048

Gnomad4 AFR AF: 0.0000245

Gnomad4 AMR AF: 0.00

Gnomad4 ASJ AF: 0.00

Gnomad4 EAS AF: 0.00

Gnomad4 SAS AF: 0.00

Gnomad4 FIN AF: 0.000302

Gnomad4 NFE AF: 0.00

Gnomad4 OTH AF: 0.00

Alfa AF: 0.0112 Hom.: 0

ClinVar

Significance: Uncertain significance

Submissions summary: Uncertain:3

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

not specified Uncertain:1

May 10, 2019

Laboratory for Molecular Medicine, Mass General Brigham Personalized Medicine

Significance: Uncertain significance

Review Status: criteria provided, single submitter

Collection Method: clinical testing

The c.50143+1G>A variant in TTN has been identified in 1 individual with DCM (LMM data). It has also been identified in 0.05% (34/72786) of European chromosomes by gnomAD (http://gnomad.broadinstitute.org); however, the sequencing quality of this region was low. This variant occurs in the invariant region (+/- 1, 2) of the splice consensus sequence and is predicted to cause altered splicing leading to an abnormal or absent protein. Splice site variants and other truncating variants in TTN are associated with DCM if they impact the exons encoding for the A-band (Herman 2012, Pugh 2014), where this variant is located, and/or are located in an exon that is highly expressed in the heart (Roberts 2015). In summary, the clinical significance of the c.50143+1G>A variant is uncertain. ACMG/AMP Criteria applied: PVS1_Moderate. -

Cardiomyopathy Uncertain:1

Aug 08, 2019

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

Significance: Uncertain significance

Review Status: criteria provided, single submitter

Collection Method: clinical testing

- -

Cardiovascular phenotype Uncertain:1

Nov 21, 2022

Ambry Genetics

Significance: Uncertain significance

Review Status: criteria provided, single submitter

Collection Method: clinical testing

The c.30652+1G>A intronic variant results from a G to A substitution one nucleotide after coding exon 122 of the TTN gene. Coding exon 122 is located in the A-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 (referred to as c.50143+1G>A) has been detected in an individual with dilated cardiomyopathy (DCM) who also had variants in other cardiac-related genes (Pugh TJ et al. Genet. Med., 2014 Aug;16:601-8). This nucleotide position is highly conserved in available vertebrate species. In silico splice site analysis predicts that this alteration will weaken the native splice donor site and may result in the creation or strengthening of a novel splice donor site. This alteration disrupts the canonical splice site and is expected to cause aberrant splicing. 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. 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
BayesDel_addAF	Pathogenic	0.45	D
BayesDel_noAF	Pathogenic	0.41
CADD	Pathogenic	34
DANN	Uncertain	0.99
Eigen	Pathogenic	1.2
Eigen_PC	Pathogenic	1.1
FATHMM_MKL	Pathogenic	0.99	D
GERP RS		6.1

Splicing

Name	Calibrated prediction	Score	Prediction
dbscSNV1_ADA	Pathogenic	1.0
dbscSNV1_RF	Pathogenic	0.93
SpliceAI score (max)		0.98		Details are displayed if max score is > 0.2
DS_DG_spliceai		0.46		Position offset: -3
DS_DL_spliceai		0.98		Position offset: 1

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

Publications

LitVar

Other links and lift over

dbSNP: rs397517631; hg19: chr2-179460233;