2-178581939-C-T

Position:

• chr2-178581939-C-T

Variant summary

Our verdict is Likely benign. Variant got -2 ACMG points: 1P and 3B. PP2 BP4_Moderate BP6

The NM_001267550.2(TTN):​c.66430G>A​(p.Ala22144Thr) variant causes a missense change involving the alteration of a non-conserved nucleotide. The variant allele was found at a frequency of 0.000464 in 1,613,062 control chromosomes in the GnomAD database, with no homozygous occurrence. In-silico tool predicts a benign outcome for this variant. 16/19 in silico tools predict a benign outcome for this variant. Variant has been reported in ClinVar as Conflicting classifications of pathogenicity (no stars). Another variant affecting the same amino acid position, but resulting in a different missense (i.e. A22144S) has been classified as Uncertain significance.

• Frequency:
  • Genomes: 𝑓 0.00025 (0 hom., cov: 32)
  • Exomes 𝑓: 0.00049 (0 hom.)
• Consequence: TTN NM_001267550.2 missense
• Clinical Significance: Conflicting classifications of pathogenicity criteria provided, conflicting classifications U:6 B:3
• Conservation: PhyloP100: 2.25

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_benign. Variant got -2 ACMG points.

• 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.
• BP4: Computational evidence support a benign effect (MetaRNN=0.076449275).
• BP6: Variant 2-178581939-C-T is Benign according to our data. Variant chr2-178581939-C-T is described in ClinVar as [Conflicting_classifications_of_pathogenicity]. Clinvar id is 238827.We mark this variant Likely_benign, oryginal submissions are: {Likely_benign=3, Uncertain_significance=6}. Variant chr2-178581939-C-T is described in Lovd as [Likely_benign].

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	UniProt
TTN	NM_001267550.2	c.66430G>A	p.Ala22144Thr	missense_variant	315/363	ENST00000589042.5
TTN-AS1	NR_038272.1	n.2044-633C>T		intron_variant, non_coding_transcript_variant

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Appris	UniProt
TTN	ENST00000589042.5	c.66430G>A	p.Ala22144Thr	missense_variant	315/363	5	NM_001267550.2	P1
TTN-AS1	ENST00000659121.1	n.417-15657C>T		intron_variant, non_coding_transcript_variant

Frequencies

GnomAD3 genomes AF: 0.000250 AC: 38 AN: 152074 Hom.: 0 Cov.: 32

Gnomad AFR AF: 0.000217

Gnomad AMI AF: 0.00

Gnomad AMR AF: 0.000524

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: 0.000279

Gnomad OTH AF: 0.000957

GnomAD3 exomes AF: 0.000274 AC: 68 AN: 248372 Hom.: 0 AF XY: 0.000282 AC XY: 38 AN XY: 134786

Gnomad AFR exome AF: 0.000259

Gnomad AMR exome AF: 0.000552

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: 0.000400

Gnomad OTH exome AF: 0.00

GnomAD4 exome AF: 0.000487 AC: 711 AN: 1460988 Hom.: 0 Cov.: 32 AF XY: 0.000482 AC XY: 350 AN XY: 726772

Gnomad4 AFR exome AF: 0.000209

Gnomad4 AMR exome AF: 0.000537

Gnomad4 ASJ exome AF: 0.00

Gnomad4 EAS exome AF: 0.0000505

Gnomad4 SAS exome AF: 0.0000116

Gnomad4 FIN exome AF: 0.00

Gnomad4 NFE exome AF: 0.000590

Gnomad4 OTH exome AF: 0.000348

GnomAD4 genome AF: 0.000250 AC: 38 AN: 152074 Hom.: 0 Cov.: 32 AF XY: 0.000162 AC XY: 12 AN XY: 74258

Gnomad4 AFR AF: 0.000217

Gnomad4 AMR AF: 0.000524

Gnomad4 ASJ AF: 0.00

Gnomad4 EAS AF: 0.00

Gnomad4 SAS AF: 0.00

Gnomad4 FIN AF: 0.00

Gnomad4 NFE AF: 0.000279

Gnomad4 OTH AF: 0.000957

Alfa AF: 0.000398 Hom.: 0

Bravo AF: 0.000268

TwinsUK AF: 0.000539 AC: 2

ALSPAC AF: 0.000259 AC: 1

ESP6500AA AF: 0.000261 AC: 1

ESP6500EA AF: 0.000242 AC: 2

ExAC AF: 0.000174 AC: 21

EpiCase AF: 0.000164

EpiControl AF: 0.000415

ClinVar

Significance: Conflicting classifications of pathogenicity

Submissions summary: Uncertain:6 Benign:3

Revision: criteria provided, conflicting classifications

Submissions by phenotype

not provided Uncertain:3 Benign:1

Uncertain significance, criteria provided, single submitter	clinical testing	Mayo Clinic Laboratories, Mayo Clinic	Jun 17, 2019	- -
Uncertain significance, criteria provided, single submitter	clinical testing	Revvity Omics, Revvity	Jun 16, 2022	- -
Uncertain significance, criteria provided, single submitter	clinical testing	Eurofins Ntd Llc (ga)	Aug 13, 2018	- -
Likely benign, criteria provided, single submitter	clinical testing	GeneDx	Nov 20, 2020	This variant is associated with the following publications: (PMID: 26498160, 27930701, 30847666) -

not specified Uncertain:1 Benign:1

Likely benign, criteria provided, single submitter	clinical testing	Women's Health and Genetics/Laboratory Corporation of America, LabCorp	Nov 21, 2023	Variant summary: TTN c.58726G>A (p.Ala19576Thr) results in a non-conservative amino acid change located in the A-band of the encoded protein sequence. Two of four in-silico tools predict a benign effect of the variant on protein function. The variant allele was found at a frequency of 0.00027 in 248372 control chromosomes, predominantly at a frequency of 0.00055 within the Latino subpopulation in the gnomAD database. The observed variant frequency within Latino control individuals in the gnomAD database is approximately 1.41 fold of the estimated maximal expected allele frequency for a pathogenic variant in TTN causing Dilated Cardiomyopathy phenotype (0.00039), strongly suggesting that the variant is a benign polymorphism found primarily in populations of Latino origin. c.58726G>A has been reported in the literature in individuals affected with sudden cardiac death (e.g. Nunn_2016, Sanchez_2016) or HCM (van Lint_2019). These report(s) do not provide unequivocal conclusions about association of the variant with Dilated Cardiomyopathy. To our knowledge, no experimental evidence demonstrating an impact on protein function has been reported. The following publications have been ascertained in the context of this evaluation (PMID: 26498160, 27930701, 30847666). Eight submitters have cited clinical-significance assessments for this variant to ClinVar after 2014. Multiple submitters reported the variant with conflicting assessments (likely benign n=2, VUS n=6). Based on the evidence outlined above, the variant was classified as likely benign. -
Uncertain significance, criteria provided, single submitter	clinical testing	Laboratory for Molecular Medicine, Mass General Brigham Personalized Medicine	Jan 22, 2018	Variant classified as Uncertain Significance - Favor Benign. The p.Ala19576Thr v ariant in TTN has not been previously reported in individuals with cardiomyopath y, but has been identified in 0.06% (19/34344) of Latino chromosomes, 0.04% (9/2 4000) of African chromosomes, and 0.04% (45/126096) of European chromosomes by t he Genome Aggregation Database (gnomAD, http://gnomad.broadinstitute.org; dbSNP rs183276016). It has been also reported in ClinVar (Variation ID:238827). Comput ational prediction tools and conservation analysis do not provide strong support for or against an impact to the protein. In summary, while the clinical signifi cance of the p.Ala19576Thr variant is uncertain, its frequency suggests that it is more likely to be benign. ACMG/AMP Criteria applied: BS1_Supporting. -

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

Nov 14, 2017

- -

Autosomal recessive limb-girdle muscular dystrophy type 2J;C1838244:Tibial muscular dystrophy;C1858763:Dilated cardiomyopathy 1G;C1861065:Hypertrophic cardiomyopathy 9;C1863599:Myopathy, myofibrillar, 9, with early respiratory failure;C2673677:Early-onset myopathy with fatal cardiomyopathy Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Fulgent Genetics, Fulgent Genetics

Oct 31, 2018

- -

Cardiovascular phenotype Benign:1

Likely benign, criteria provided, single submitter

clinical testing

Ambry Genetics

Jun 16, 2020

This alteration is classified as likely benign based on a combination of the following: seen in unaffected individuals, population frequency, intact protein function, lack of segregation with disease, co-occurrence, RNA analysis, in silico models, amino acid conservation, lack of disease association in case-control studies, and/or the mechanism of disease or impacted region is inconsistent with a known cause of pathogenicity. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Benign	0.11
BayesDel_addAF	Benign	-0.37	T
BayesDel_noAF	Benign	-0.42
CADD	Benign	22
DANN	Benign	0.95
Eigen	Benign	0.12
Eigen_PC	Uncertain	0.26
FATHMM_MKL	Uncertain	0.93	D
LIST_S2	Uncertain	0.90	D;D;D;.;D;D;D
M_CAP	Benign	0.0094	T
MetaRNN	Benign	0.076	T;T;T;T;T;T;T
MetaSVM	Benign	-0.91	T
MutationAssessor	Benign	1.1	.;.;.;L;.;.;L
MutationTaster	Benign	0.79	D;D;D;D;D;D
PrimateAI	Benign	0.40	T
PROVEAN	Benign	-2.2	N;N;.;.;N;N;.
REVEL	Benign	0.14
Sift	Benign	0.10	T;T;.;.;T;T;.
Polyphen		0.61	.;.;.;P;.;.;P
Vest4		0.26
MVP		0.22
MPC		0.10
ClinPred		0.026	T
GERP RS		5.6

Splicing

Name	Calibrated prediction	Score	Prediction
SpliceAI score (max)		0.010		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: rs183276016; hg19: chr2-179446666;