rs370267738

chr2-178527124-G-Achr2-178527124-G-T

Variant summary

Our verdict is Uncertain significance. Variant got 4 ACMG points: 5P and 1B. PM1 PM2 PP2 BP4

The NM_001267550.2(TTN):c.107864C>T(p.Thr35955Ile) variant causes a missense change. The variant allele was found at a frequency of 0.000000684 in 1,461,678 control chromosomes in the GnomAD database, with no homozygous occurrence. In-silico tool predicts a benign outcome for this variant. Variant has been reported in ClinVar as Uncertain significance (★). Another variant affecting the same amino acid position, but resulting in a different missense (i.e. T35955N) has been classified as Uncertain significance.

• Frequency:
  • Genomes: not found (cov: 33)
  • Exomes 𝑓: 6.8e-7 (0 hom.)
• Consequence: TTN NM_001267550.2 missense
• Clinical Significance: Uncertain significance criteria provided, single submitter U:1
• Conservation: PhyloP100: 6.67

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 4 ACMG points.

• PM1: In a hotspot region, there are 2 aminoacids with missense pathogenic changes in the window of +-8 aminoacids around while only 0 benign, 8 uncertain in NM_001267550.2
• PM2: Very rare variant in population databases, with high coverage
• PP2: Missense variant where missense usually causes diseases, TTN
• BP4: Computational evidence support a benign effect (MetaRNN=0.3686025).

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	UniProt
TTN	NM_001267550.2	c.107864C>T	p.Thr35955Ile	missense_variant	363/363	ENST00000589042.5
TTN-AS1	NR_038272.1	n.219+3488G>A		intron_variant, non_coding_transcript_variant

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Appris	UniProt
TTN	ENST00000589042.5	c.107864C>T	p.Thr35955Ile	missense_variant	363/363	5	NM_001267550.2	P1
TTN-AS1	ENST00000659121.1	n.416+3488G>A		intron_variant, non_coding_transcript_variant

Frequencies

GnomAD3 genomes Cov.: 33

GnomAD4 exome AF: 6.84e-7 AC: 1 AN: 1461678 Hom.: 0 Cov.: 32 AF XY: 0.00000138 AC XY: 1 AN XY: 727118

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.: 33

ClinVar

Significance: Uncertain significance

Submissions summary: Uncertain:1

Revision: criteria provided, single submitter

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

Invitae

Dec 04, 2023

This sequence change replaces threonine, which is neutral and polar, with isoleucine, which is neutral and non-polar, at codon 35955 of the TTN protein (p.Thr35955Ile). This variant is not present in population databases (gnomAD no frequency). This variant has not been reported in the literature in individuals affected with TTN-related conditions. ClinVar contains an entry for this variant (Variation ID: 466774). Experimental studies and prediction algorithms are not available or were not evaluated, and the functional significance of this variant is currently unknown. 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 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. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Pathogenic	0.68
BayesDel_addAF	Uncertain	0.13	D
BayesDel_noAF	Uncertain	-0.050
Cadd	Benign	20
Dann	Benign	0.84
Eigen	Pathogenic	0.76
Eigen_PC	Pathogenic	0.73
FATHMM_MKL	Pathogenic	0.97	D
LIST_S2	Uncertain	0.92	D;D;D;.;D;D;D
M_CAP	Benign	0.020	T
MetaRNN	Benign	0.37	T;T;T;T;T;T;T
MetaSVM	Uncertain	0.070	D
MutationTaster	Benign	1.0	D;D;D;D;D;D
PrimateAI	Uncertain	0.72	T
PROVEAN	Uncertain	-4.3	D;D;.;.;D;D;.
REVEL	Uncertain	0.47
Polyphen		1.0	.;.;.;D;.;.;D
Vest4		0.40
MutPred		0.58		.;.;.;Loss of phosphorylation at T34309 (P = 0.2597);.;.;Loss of phosphorylation at T34309 (P = 0.2597);
MVP		0.62
MPC		0.47
ClinPred		0.28	T
GERP RS		6.1

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: rs370267738; hg19: chr2-179391851;