2-178547089-T-C

Position:

• chr2-178547089-T-C

Variant summary

Our verdict is Uncertain significance. Variant got 5 ACMG points: 5P and 0B. PM2 PP2 PP3_Moderate

The NM_001267550.2(TTN):​c.94436A>G​(p.Tyr31479Cys) variant causes a missense change involving the alteration of a conserved nucleotide. The variant was absent in control chromosomes in GnomAD project. In-silico tool predicts a pathogenic outcome for this variant. Variant has been reported in ClinVar as Uncertain significance (★★).

• Frequency: Genomes: not found (cov: 33)
• Consequence: TTN NM_001267550.2 missense
• Clinical Significance: Uncertain significance criteria provided, multiple submitters, no conflicts U:2
• Conservation: PhyloP100: 8.02

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 5 ACMG points.

• PM2: Very rare variant in population databases, with high coverage
• PP2: Missense variant in gene, where missense usually causes diseases (based on misZ statistic), TTN. . Gene score misZ -1.1021 (greater than the threshold 3.09). Trascript score misZ 6.9794 (greater than threshold 3.09). GenCC has associacion of gene with dilated cardiomyopathy, tibial muscular dystrophy, early-onset myopathy with fatal cardiomyopathy, autosomal recessive centronuclear myopathy, hypertrophic cardiomyopathy, hypertrophic cardiomyopathy 9, TTN-related myopathy, dilated cardiomyopathy 1G, arrhythmogenic right ventricular cardiomyopathy, myopathy, myofibrillar, 9, with early respiratory failure, familial isolated dilated cardiomyopathy, childhood-onset progressive contractures-limb-girdle weakness-muscle dystrophy syndrome, autosomal recessive limb-girdle muscular dystrophy type 2J.
• PP3: MetaRNN computational evidence supports a deleterious effect, 0.921

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
TTN	NM_001267550.2	c.94436A>G	p.Tyr31479Cys	missense_variant	340/363	ENST00000589042.5	NP_001254479.2
TTN-AS1	NR_038272.1	n.2043+4728T>C		intron_variant, non_coding_transcript_variant

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
TTN	ENST00000589042.5	c.94436A>G	p.Tyr31479Cys	missense_variant	340/363	5	NM_001267550.2	ENSP00000467141	P1
TTN-AS1	ENST00000659121.1	n.416+23453T>C		intron_variant, non_coding_transcript_variant

Frequencies

GnomAD3 genomes Cov.: 33

GnomAD4 exome Cov.: 34

GnomAD4 genome Cov.: 33

Alfa AF: 0.0000329 Hom.: 0

Bravo AF: 0.0000151

ClinVar

Significance: Uncertain significance

Submissions summary: Uncertain:2

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

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

Jul 10, 2017

This variant identified in the TTN gene is located in the A band of the resulting protein (PMID: 25589632). It is unclear how this variant impacts the function of this protein. Algorithms developed to predict the effect of missense changes on protein structure and function are unavailable for the TTN gene. 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 create or strengthen a splice site, but this prediction has not been confirmed by published transcriptional studies. This variant has not been reported in the literature in individuals with TTN-related disease. This variant is not present in population databases (ExAC no frequency). This sequence change replaces tyrosine with cysteine at codon 31479 of the TTN protein (p.Tyr31479Cys). There is a large physicochemical difference between tyrosine and cysteine. -

Cardiovascular phenotype Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Ambry Genetics

Jan 16, 2020

The p.Y22414C variant (also known as c.67241A>G), located in coding exon 167 of the TTN gene, results from an A to G substitution at nucleotide position 67241. The tyrosine at codon 22414 is replaced by cysteine, an amino acid with highly dissimilar properties. This amino acid position is highly conserved in available vertebrate species. In addition, this alteration is predicted to be deleterious by in silico analysis. 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
AlphaMissense	Pathogenic	0.99
BayesDel_addAF	Pathogenic	0.26	D
BayesDel_noAF	Pathogenic	0.14
CADD	Benign	22
DANN	Benign	0.95
Eigen	Pathogenic	1.0
Eigen_PC	Pathogenic	0.96
FATHMM_MKL	Pathogenic	0.98	D
LIST_S2	Uncertain	0.96	D;D;D;.;D;D;D
M_CAP	Uncertain	0.28	D
MetaRNN	Pathogenic	0.92	D;D;D;D;D;D;D
MetaSVM	Pathogenic	1.0	D
MutationAssessor	Pathogenic	3.8	.;.;.;H;.;.;H
MutationTaster	Benign	1.0	D;D;D;D;D;D
PrimateAI	Pathogenic	0.85	D
PROVEAN	Pathogenic	-6.7	D;D;.;.;D;D;.
REVEL	Pathogenic	0.88
Sift	Uncertain	0.0010	D;D;.;.;D;D;.
Polyphen		1.0	.;.;.;D;.;.;D
Vest4		0.62
MutPred		0.91		.;.;.;Loss of MoRF binding (P = 0.3087);.;.;Loss of MoRF binding (P = 0.3087);
MVP		0.92
MPC		0.52
ClinPred		0.67	D
GERP RS		6.0

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: rs879013044; hg19: chr2-179411816; COSMIC: COSV60097592; COSMIC: COSV60097592;