18-31591964-G-C

Position:

• chr18-31591964-G-C

Variant summary

Our verdict is Uncertain significance. Variant got 0 ACMG points: 4P and 4B. PM1 PM2 BP4_Strong

The ENST00000237014.8(TTR):​c.62G>C​(p.Gly21Ala) 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 1,461,820 control chromosomes in the GnomAD database, with no homozygous occurrence. In-silico tool predicts a benign outcome for this variant. 16/21 in silico tools predict a benign outcome for this variant. Variant has been reported in ClinVar as Uncertain significance (★★).

• Frequency:
  • Genomes: not found (cov: 33)
  • Exomes 𝑓: 6.8e-7 (0 hom.)
• Consequence: TTR ENST00000237014.8 missense
• Clinical Significance: Uncertain significance criteria provided, multiple submitters, no conflicts U:3
• Conservation: PhyloP100: 0.975

Genes affected

TTR (HGNC:12405): (transthyretin) This gene encodes one of the three prealbumins, which include alpha-1-antitrypsin, transthyretin and orosomucoid. The encoded protein, transthyretin, is a homo-tetrameric carrier protein, which transports thyroid hormones in the plasma and cerebrospinal fluid. It is also involved in the transport of retinol (vitamin A) in the plasma by associating with retinol-binding protein. The protein may also be involved in other intracellular processes including proteolysis, nerve regeneration, autophagy and glucose homeostasis. Mutations in this gene are associated with amyloid deposition, predominantly affecting peripheral nerves or the heart, while a small percentage of the gene mutations are non-amyloidogenic. The mutations are implicated in the etiology of several diseases, including amyloidotic polyneuropathy, euthyroid hyperthyroxinaemia, amyloidotic vitreous opacities, cardiomyopathy, oculoleptomeningeal amyloidosis, meningocerebrovascular amyloidosis and carpal tunnel syndrome. [provided by RefSeq, Aug 2017]

ACMG classification

Verdict is Uncertain_significance. Variant got 0 ACMG points.

• PM1: In a chain Transthyretin (size 126) in uniprot entity TTHY_HUMAN there are 268 pathogenic changes around while only 13 benign (95%) in ENST00000237014.8
• PM2: Very rare variant in population databases, with high coverage
• BP4: Computational evidence support a benign effect (MetaRNN=0.05705449).

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
TTR	NM_000371.4	c.62G>C	p.Gly21Ala	missense_variant	1/4	ENST00000237014.8	NP_000362.1

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
TTR	ENST00000237014.8	c.62G>C	p.Gly21Ala	missense_variant	1/4	1	NM_000371.4	ENSP00000237014	P1

Frequencies

GnomAD3 genomes Cov.: 33

GnomAD4 exome AF: 6.84e-7 AC: 1 AN: 1461820 Hom.: 0 Cov.: 30 AF XY: 0.00 AC XY: 0 AN XY: 727210

Gnomad4 AFR exome AF: 0.00

Gnomad4 AMR exome AF: 0.00

Gnomad4 ASJ exome AF: 0.00

Gnomad4 EAS exome AF: 0.0000252

Gnomad4 SAS exome AF: 0.00

Gnomad4 FIN exome AF: 0.00

Gnomad4 NFE exome AF: 0.00

Gnomad4 OTH exome AF: 0.00

GnomAD4 genome Cov.: 33

Bravo AF: 0.00000378

ClinVar

Significance: Uncertain significance

Submissions summary: Uncertain:3

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

Cardiomyopathy Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

CHEO Genetics Diagnostic Laboratory, Children's Hospital of Eastern Ontario

Aug 04, 2021

- -

Cardiovascular phenotype Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Ambry Genetics

Oct 24, 2023

The p.G21A variant (also known as c.62G>C), located in coding exon 1 of the TTR gene, results from a G to C substitution at nucleotide position 62. The glycine at codon 21 is replaced by alanine, an amino acid with similar properties. This amino acid position is not well conserved in available vertebrate species. In addition, this alteration is predicted to be tolerated by in silico analysis. Since supporting evidence is limited at this time, the clinical significance of this alteration remains unclear. -

Amyloidosis, hereditary systemic 1 Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Labcorp Genetics (formerly Invitae), Labcorp

Dec 04, 2023

This sequence change replaces glycine, which is neutral and non-polar, with alanine, which is neutral and non-polar, at codon 21 of the TTR protein (p.Gly21Ala). This variant is not present in population databases (gnomAD no frequency). This variant has not been reported in the literature in individuals affected with TTR-related conditions. ClinVar contains an entry for this variant (Variation ID: 470719). Advanced modeling of protein sequence and biophysical properties (such as structural, functional, and spatial information, amino acid conservation, physicochemical variation, residue mobility, and thermodynamic stability) performed at Invitae indicates that this missense variant is not expected to disrupt TTR protein function with a negative predictive value of 95%. 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	Benign	0.072
BayesDel_addAF	Benign	-0.042	T
BayesDel_noAF	Benign	-0.30
CADD	Benign	6.8
DANN	Benign	0.55
DEOGEN2	Benign	0.16	T;T;T;.
Eigen	Benign	-1.2
Eigen_PC	Benign	-1.2
FATHMM_MKL	Benign	0.079	N
LIST_S2	Benign	0.81	.;T;T;T
M_CAP	Benign	0.052	D
MetaRNN	Benign	0.057	T;T;T;T
MetaSVM	Benign	-0.52	T
MutationAssessor	Benign	1.2	L;L;.;.
MutationTaster	Benign	1.0	N
PrimateAI	Benign	0.30	T
PROVEAN	Benign	-0.11	.;N;.;.
REVEL	Benign	0.094
Sift	Benign	0.56	.;T;.;.
Sift4G	Benign	1.0	.;T;T;T
Polyphen		0.0020	B;B;.;.
Vest4		0.048, 0.12, 0.089
MutPred		0.23		Loss of catalytic residue at A20 (P = 0.0554);Loss of catalytic residue at A20 (P = 0.0554);Loss of catalytic residue at A20 (P = 0.0554);Loss of catalytic residue at A20 (P = 0.0554);
MVP		0.78
MPC		0.50
ClinPred		0.065	T
GERP RS		0.87
Varity_R		0.13
gMVP		0.85

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: rs1469623969; hg19: chr18-29171927;