2-178785999-C-A

Position:

• chr2-178785999-C-A

Variant summary

Our verdict is Uncertain significance. Variant got 4 ACMG points: 4P and 0B. PM2 PP2 PP5

The NM_001267550.2(TTN):​c.2219G>T​(p.Arg740Leu) variant causes a missense change involving the alteration of a non-conserved nucleotide. The variant allele was found at a frequency of 0.000000684 in 1,461,822 control chromosomes in the GnomAD database, with no homozygous occurrence. 12/18 in silico tools predict a benign outcome for this variant. Variant has been reported in ClinVar as Pathogenic (no stars). Another variant affecting the same amino acid position, but resulting in a different missense (i.e. R740S) has been classified as Likely benign.

• Frequency:
  • Genomes: not found (cov: 32)
  • Exomes 𝑓: 6.8e-7 (0 hom.)
• Consequence: TTN NM_001267550.2 missense
• Clinical Significance: Pathogenic no assertion criteria provided P:1
• Conservation: PhyloP100: 0.627

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]

ACMG classification

Verdict is Uncertain_significance. Variant got 4 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.
• PP5: Variant 2-178785999-C-A is Pathogenic according to our data. Variant chr2-178785999-C-A is described in ClinVar as [Pathogenic]. Clinvar id is 12649.Status of the report is no_assertion_criteria_provided, 0 stars. Variant chr2-178785999-C-A is described in Lovd as [Pathogenic].

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	UniProt
TTN	NM_001267550.2	c.2219G>T	p.Arg740Leu	missense_variant	14/363	ENST00000589042.5
TTN	NM_133379.5	c.2219G>T	p.Arg740Leu	missense_variant	14/46	ENST00000360870.10

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Appris	UniProt
TTN	ENST00000589042.5	c.2219G>T	p.Arg740Leu	missense_variant	14/363	5	NM_001267550.2	P1
TTN	ENST00000360870.10	c.2219G>T	p.Arg740Leu	missense_variant	14/46	5	NM_133379.5

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD4 exome AF: 6.84e-7 AC: 1 AN: 1461822 Hom.: 0 Cov.: 35 AF XY: 0.00000138 AC XY: 1 AN XY: 727212

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: 8.99e-7

Gnomad4 OTH exome AF: 0.00

GnomAD4 genome Cov.: 32

ClinVar

Significance: Pathogenic

Submissions summary: Pathogenic:1

Revision: no assertion criteria provided

Submissions by phenotype

Hypertrophic cardiomyopathy 9 Pathogenic:1

Pathogenic, no assertion criteria provided

literature only

OMIM

Aug 27, 1999

- -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Benign	0.12
BayesDel_addAF	Uncertain	0.068	T
BayesDel_noAF	Benign	-0.14
CADD	Benign	8.0
DANN	Benign	0.36
Eigen	Benign	-1.1
Eigen_PC	Benign	-1.0
FATHMM_MKL	Benign	0.66	D
LIST_S2	Uncertain	0.87	D;D;D;.;D;D;T;D
M_CAP	Benign	0.029	D
MetaRNN	Uncertain	0.56	D;D;D;D;D;D;D;D
MetaSVM	Benign	-0.95	T
MutationTaster	Benign	0.0000031	A;A;A;A;A;A;A
PrimateAI	Benign	0.22	T
PROVEAN	Benign	-2.0	N;N;.;.;N;N;.;N
REVEL	Uncertain	0.32
Sift	Benign	0.067	T;D;.;.;T;T;.;D
Sift4G	Benign	0.45	.;.;.;.;.;.;.;T
Polyphen		0.0, 0.0010	.;.;.;B;.;.;B;B
Vest4		0.51
MutPred		0.47		Loss of phosphorylation at S742 (P = 0.0497);.;Loss of phosphorylation at S742 (P = 0.0497);Loss of phosphorylation at S742 (P = 0.0497);.;.;Loss of phosphorylation at S742 (P = 0.0497);Loss of phosphorylation at S742 (P = 0.0497);
MVP		0.21
MPC		0.10
ClinPred		0.074	T
GERP RS		1.2

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: rs28933405; hg19: chr2-179650726;