2-178604269-G-A

Variant names:

• chr2-178604269-G-A
• rs747236787
• NM_001267550.2:c.54418C>T

Variant summary

Our verdict is Pathogenic. The variant received 18 ACMG points: 18P and 0B. PVS1 PM2 PP5_Very_Strong

The NM_001267550.2(TTN):​c.54418C>T​(p.Arg18140*) variant causes a stop gained change involving the alteration of a non-conserved nucleotide. The variant allele was found at a frequency of 0.00000214 in 1,400,692 control chromosomes in the GnomAD database, with no homozygous occurrence. In-silico tool predicts a pathogenic outcome for this variant. Variant has been reported in ClinVar as Likely pathogenic (★★). Variant results in nonsense mediated mRNA decay.

• Frequency:
  • Genomes: not found (cov: 32)
  • Exomes 𝑓: 0.0000021 (0 hom.)
• Consequence: TTN NM_001267550.2 stop_gained
• Clinical Significance: Pathogenic/Likely pathogenic criteria provided, multiple submitters, no conflicts P:6
• Conservation: PhyloP100: 2.59
• Publications: 1 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: Pathogenic. The variant received 18 ACMG points.

• PVS1: Loss of function variant, product undergoes nonsense mediated mRNA decay. LoF is a known mechanism of disease.
• PM2: Very rare variant in population databases, with high coverage
• PP5: Variant 2-178604269-G-A is Pathogenic according to our data. Variant chr2-178604269-G-A is described in ClinVar as Pathogenic/Likely_pathogenic. ClinVar VariationId is 579797.Status of the report is criteria_provided_multiple_submitters_no_conflicts, 2 stars.

Variant Effect in Transcripts

ACMG analysis was done for transcript: NM_001267550.2. You can select a different transcript below to see updated ACMG assignments.

RefSeq Transcripts

Sel.	Gene	Transcript	Tags	HGVSc	HGVSp	Effect	Exon Rank	Protein	UniProt
	TTN	NM_001267550.2	MANE Select	c.54418C>T	p.Arg18140*	stop_gained	Exon 282 of 363	NP_001254479.2	Q8WZ42-12
	TTN	NM_001256850.1		c.49495C>T	p.Arg16499*	stop_gained	Exon 232 of 313	NP_001243779.1	Q8WZ42-1
	TTN	NM_133378.4		c.46714C>T	p.Arg15572*	stop_gained	Exon 231 of 312	NP_596869.4	Q8WZ42-11

Ensembl Transcripts

Sel.	Gene	Transcript	Tags	HGVSc	HGVSp	Effect	Exon Rank	Protein	UniProt
	TTN	ENST00000589042.5	TSL:5 MANE Select	c.54418C>T	p.Arg18140*	stop_gained	Exon 282 of 363	ENSP00000467141.1	Q8WZ42-12
	TTN	ENST00000446966.2	TSL:1	c.54262C>T	p.Arg18088*	stop_gained	Exon 280 of 361	ENSP00000408004.2	A0A1B0GXE3
	TTN	ENST00000436599.2	TSL:1	c.54142C>T	p.Arg18048*	stop_gained	Exon 280 of 361	ENSP00000405517.2	A0A0C4DG59

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD2 exomes AF: 0.00000983 AC: 2 AN: 203450 AF XY: 0.00000920

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: 0.0000209

Gnomad OTH exome AF: 0.00

GnomAD4 exome AF: 0.00000214 AC: 3 AN: 1400692 Hom.: 0 Cov.: 31 AF XY: 0.00000435 AC XY: 3 AN XY: 689722

⚠️ The allele balance in gnomAD version 4 Exomes is significantly skewed from the expected value of 0.5.

African (AFR) AF: 0.00 AC: 0 AN: 31678

American (AMR) AF: 0.00 AC: 0 AN: 38308

Ashkenazi Jewish (ASJ) AF: 0.00 AC: 0 AN: 22836

East Asian (EAS) AF: 0.00 AC: 0 AN: 38740

South Asian (SAS) AF: 0.00 AC: 0 AN: 74978

European-Finnish (FIN) AF: 0.00 AC: 0 AN: 51366

Middle Eastern (MID) AF: 0.00 AC: 0 AN: 5446

European-Non Finnish (NFE) AF: 9.26e-7 AC: 1 AN: 1079688

Other (OTH) AF: 0.0000347 AC: 2 AN: 57652

⚠️ The allele balance in gnomAD4 Exomes is highly skewed from 0.5 (p-value = 0.00846340), which strongly suggests a high chance of mosaicism in these individuals.

GnomAD4 genome Cov.: 32

ExAC AF: 0.0000166 AC: 2

ClinVar

ClinVar submissions

Significance: Pathogenic/Likely pathogenic

Revision: criteria provided, multiple submitters, no conflicts

Pathogenic	VUS	Benign	Condition
2	-	-	Dilated cardiomyopathy 1G (2)
1	-	-	Autosomal recessive limb-girdle muscular dystrophy type 2J;C1858763:Dilated cardiomyopathy 1G (1)
1	-	-	Cardiovascular phenotype (1)
1	-	-	Dilated cardiomyopathy 1G;C1861065:Hypertrophic cardiomyopathy 9 (1)
1	-	-	not provided (1)

Computational scores

Source: dbNSFP v4.9

Name	Calibrated prediction	Score	Prediction
BayesDel_addAF	Pathogenic	0.60	D
BayesDel_noAF	Pathogenic	0.62
CADD	Pathogenic	61
DANN	Uncertain	0.99
Eigen	Pathogenic	1.1
Eigen_PC	Pathogenic	0.96
FATHMM_MKL	Uncertain	0.91	D
PhyloP100		2.6
Vest4		0.94
GERP RS		5.2
Mutation Taster		=0/200	disease causing (ClinVar)

Splicing

Name	Calibrated prediction	Score	Prediction
SpliceAI score (max)		0.030		Details are displayed if max score is > 0.2

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

Other links and lift over

dbSNP: rs747236787; hg19: chr2-179468996; COSMIC: COSV60047295; COSMIC: COSV60047295;