chr2-178533814-CTTA-C

Variant names:

• chr2-178533814-CTTA-C
• rs886044414
• NM_001267550.2:c.102798_102800delTAA

Variant summary

Our verdict is Uncertain significance. Variant got 2 ACMG points: 2P and 0B. PM4_Supporting PP5

The NM_001267550.2(TTN):​c.102798_102800delTAA​(p.Asn34266del) variant causes a disruptive inframe deletion change. The variant allele was found at a frequency of 0.0000109 in 1,461,662 control chromosomes in the GnomAD database, with no homozygous occurrence. Variant has been reported in ClinVar as Conflicting classifications of pathogenicity (no stars).

• Frequency:
  • Genomes: not found (cov: 32)
  • Exomes 𝑓: 0.000011 (0 hom.)
• Consequence: TTN NM_001267550.2 disruptive_inframe_deletion
• Clinical Significance: Conflicting classifications of pathogenicity criteria provided, conflicting classifications P:2 U:4
• Conservation: PhyloP100: 6.06

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.

• PM4: Nonframeshift variant in NON repetitive region in NM_001267550.2. Strenght limited to Supporting due to length of the change: 1aa.
• PP5: Variant 2-178533814-CTTA-C is Pathogenic according to our data. Variant chr2-178533814-CTTA-C is described in ClinVar as [Conflicting_classifications_of_pathogenicity]. Clinvar id is 290291.We mark this variant Likely_pathogenic, oryginal submissions are: {Likely_pathogenic=2, Uncertain_significance=4}.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	MANE	Protein	UniProt
TTN	NM_001267550.2	c.102798_102800delTAA	p.Asn34266del	disruptive_inframe_deletion	Exon 358 of 363	ENST00000589042.5	NP_001254479.2

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	TSL	MANE	Protein	Appris	UniProt
TTN	ENST00000589042.5	c.102798_102800delTAA	p.Asn34266del	disruptive_inframe_deletion	Exon 358 of 363	5	NM_001267550.2	ENSP00000467141.1

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD3 exomes AF: 0.00000803 AC: 2 AN: 249134 Hom.: 0 AF XY: 0.0000148 AC XY: 2 AN XY: 135142

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 SAS exome AF: 0.00

Gnomad FIN exome AF: 0.00

Gnomad NFE exome AF: 0.0000177

Gnomad OTH exome AF: 0.00

GnomAD4 exome AF: 0.0000109 AC: 16 AN: 1461662 Hom.: 0 AF XY: 0.00000963 AC XY: 7 AN XY: 727114

Gnomad4 AFR exome AF: 0.0000299

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: 0.0000126

Gnomad4 OTH exome AF: 0.0000166

GnomAD4 genome Cov.: 32

ClinVar

Significance: Conflicting classifications of pathogenicity

Submissions summary: Pathogenic:2 Uncertain:4

Revision: criteria provided, conflicting classifications

Submissions by phenotype

not provided Uncertain:2

Aug 15, 2023

GeneDx

Significance: Uncertain significance

Review Status: criteria provided, single submitter

Collection Method: clinical testing

Not observed at significant frequency in large population cohorts (gnomAD); In-frame single amino acid deletion in a gene in which most reported pathogenic variants are truncating/loss of function; Located in the M-line region of TTN in which the majority of loss of function variants have been associated with autosomal recessive titinopathies (Carmignac et al., 2007); This variant is associated with the following publications: (PMID: 35081925) -

Sep 13, 2016

Eurofins Ntd Llc (ga)

Significance: Uncertain significance

Review Status: criteria provided, single submitter

Collection Method: clinical testing

- -

Autosomal recessive limb-girdle muscular dystrophy type 2J;C1858763:Dilated cardiomyopathy 1G Pathogenic:1

Jan 07, 2025

Labcorp Genetics (formerly Invitae), Labcorp

Significance: Likely pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

This variant, c.102798_102800del, results in the deletion of 1 amino acid(s) of the TTN protein (p.Asn34266del), but otherwise preserves the integrity of the reading frame. This variant is present in population databases (no rsID available, gnomAD 0.002%). This variant has been observed in individual(s) with autosomal recessive TTN-related conditions (PMID: 35081925; internal data). In at least one individual the data is consistent with being in trans (on the opposite chromosome) from a pathogenic variant. This variant has been reported in individual(s) with autosomal dominant dilated cardiomyopathy (internal data); however, the role of the variant in this condition is currently unclear. This variant is located in the M band of TTN (PMID: 25589632). Non-truncating variants in this region may be relevant for neuromuscular disorders, but have not been definitively shown to cause cardiomyopathy (PMID: 23975875). In summary, the currently available evidence indicates that the variant is pathogenic, but additional data are needed to prove that conclusively. Therefore, this variant has been classified as Likely Pathogenic. -

Multiminicore myopathy Pathogenic:1

Apr 11, 2020

Pediatric Department, Peking University First Hospital

Significance: Likely pathogenic

Review Status: criteria provided, single submitter

Collection Method: provider interpretation

- -

Cardiomyopathy Uncertain:1

Nov 28, 2016

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

Jan 30, 2023

Ambry Genetics

Significance: Uncertain significance

Review Status: criteria provided, single submitter

Collection Method: clinical testing

The c.75603_75605delTAA variant (also known as p.N25201del) is located in coding exon 185 of the TTN gene. This variant results from an in-frame TAA deletion at nucleotide positions 75603 to 75605. This results in the in-frame deletion of an asparagine at codon 25201. This alteration has been reported in a congenital myopathy cohort (Zhang Y et al. BMC Pediatr, 2022 Jan;22:65). This amino acid position is highly conserved in available vertebrate species. In addition, this alteration is predicted to be deleterious by in silico analysis (Choi Y et al. PLoS ONE. 2012; 7(10):e46688). Since supporting evidence is limited at this time, the clinical significance of this alteration remains unclear. -

Computational scores

Source: dbNSFP v4.3

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: rs886044414; hg19: chr2-179398541;