rs28937887

Positions:

• chr10-100989211-G-A
• chr10-100989211-G-T

Variant summary

Our verdict is Pathogenic. Variant got 14 ACMG points: 14P and 0B. PM1 PM2 PM5 PP5_Very_Strong

The NM_021830.5(TWNK):​c.1001G>A​(p.Arg334Gln) variant causes a missense change. The variant allele was found at a frequency of 0.00000137 in 1,461,854 control chromosomes in the GnomAD database, with no homozygous occurrence. Variant has been reported in ClinVar as Likely pathogenic (★★). Another variant affecting the same amino acid position, but resulting in a different missense (i.e. R334P) has been classified as Likely pathogenic.

• Frequency:
  • Genomes: not found (cov: 33)
  • Exomes 𝑓: 0.0000014 (0 hom.)
• Consequence: TWNK NM_021830.5 missense
• Clinical Significance: Pathogenic/Likely pathogenic criteria provided, multiple submitters, no conflicts P:6
• Conservation: PhyloP100: 4.18

Genes affected

TWNK (HGNC:1160): (twinkle mtDNA helicase) This gene encodes a hexameric DNA helicase which unwinds short stretches of double-stranded DNA in the 5' to 3' direction and, along with mitochondrial single-stranded DNA binding protein and mtDNA polymerase gamma, is thought to play a key role in mtDNA replication. The protein localizes to the mitochondrial matrix and mitochondrial nucleoids. Mutations in this gene cause infantile onset spinocerebellar ataxia (IOSCA) and progressive external ophthalmoplegia (PEO) and are also associated with several mitochondrial depletion syndromes. Alternative splicing results in multiple transcript variants encoding distinct isoforms.[provided by RefSeq, Aug 2009]

ACMG classification

Verdict is Pathogenic. Variant got 14 ACMG points.

• PM1: In a region_of_interest Required for hexamers formation and DNA helicase activity (size 251) in uniprot entity PEO1_HUMAN there are 18 pathogenic changes around while only 2 benign (90%) in NM_021830.5
• PM2: Very rare variant in population databases, with high coverage
• PM5: Other missense variant is known to change same aminoacid residue: Variant chrnull-null-null-null is described in UniProt as null.
• PP5: Variant 10-100989211-G-A is Pathogenic according to our data. Variant chr10-100989211-G-A is described in ClinVar as [Likely_pathogenic]. Clinvar id is 4623.Status of the report is criteria_provided_multiple_submitters_no_conflicts, 2 stars.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
TWNK	NM_021830.5	c.1001G>A	p.Arg334Gln	missense_variant	1/5	ENST00000311916.8	NP_068602.2

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
TWNK	ENST00000311916.8	c.1001G>A	p.Arg334Gln	missense_variant	1/5	1	NM_021830.5	ENSP00000309595	P1

Frequencies

GnomAD3 genomes Cov.: 33

GnomAD4 exome AF: 0.00000137 AC: 2 AN: 1461854 Hom.: 0 Cov.: 32 AF XY: 0.00 AC XY: 0 AN XY: 727234

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: 0.00000180

Gnomad4 OTH exome AF: 0.00

GnomAD4 genome Cov.: 33

ClinVar

Significance: Pathogenic/Likely pathogenic

Submissions summary: Pathogenic:6

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

not provided Pathogenic:2

Pathogenic, criteria provided, single submitter	clinical testing	Labcorp Genetics (formerly Invitae), Labcorp	Dec 03, 2023	This sequence change replaces arginine, which is basic and polar, with glutamine, which is neutral and polar, at codon 334 of the TWNK protein (p.Arg334Gln). This variant is not present in population databases (gnomAD no frequency). This missense change has been observed in individuals with clinical features of autosomal dominant progressive external ophthalmoplegia with mitochondrial DNA deletions (PMID: 12707443, 18973250, 24086434; Invitae). It has also been observed to segregate with disease in related individuals. ClinVar contains an entry for this variant (Variation ID: 4623). 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 expected to disrupt TWNK protein function with a positive predictive value of 80%. Experimental studies are conflicting or provide insufficient evidence to determine the effect of this variant on TWNK function (PMID: 19084593, 20659899, 30496414). This variant disrupts the p.Arg334 amino acid residue in TWNK. Other variant(s) that disrupt this residue have been determined to be pathogenic (PMID: 18575922). This suggests that this residue is clinically significant, and that variants that disrupt this residue are likely to be disease-causing. For these reasons, this variant has been classified as Pathogenic. -
Pathogenic, criteria provided, single submitter	clinical testing	CeGaT Center for Human Genetics Tuebingen	Aug 01, 2016	- -

Mitochondrial disease Pathogenic:1

Pathogenic, no assertion criteria provided

clinical testing

Wellcome Centre for Mitochondrial Research, Newcastle University

Apr 07, 2017

- -

Progressive external ophthalmoplegia with mitochondrial DNA deletions, autosomal dominant 3 Pathogenic:1

Likely pathogenic, criteria provided, single submitter

clinical testing

MGZ Medical Genetics Center

Dec 08, 2021

- -

Infantile onset spinocerebellar ataxia Pathogenic:1

Pathogenic, criteria provided, single submitter

clinical testing

Genomics England Pilot Project, Genomics England

-

- -

Progressive external ophthalmoplegia with mitochondrial DNA deletions, digenic Pathogenic:1

Pathogenic, no assertion criteria provided

literature only

OMIM

Aug 01, 2003

- -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Benign	0.13
BayesDel_addAF	Pathogenic	0.45	D
BayesDel_noAF	Pathogenic	0.41
CADD	Uncertain	25
DANN	Uncertain	1.0
DEOGEN2	Benign	0.19	T;.
Eigen	Uncertain	0.33
Eigen_PC	Uncertain	0.36
FATHMM_MKL	Uncertain	0.93	D
LIST_S2	Uncertain	0.89	D;D
M_CAP	Pathogenic	0.32	D
MetaRNN	Uncertain	0.70	D;D
MetaSVM	Uncertain	0.73	D
MutationAssessor	Uncertain	2.1	M;M
MutationTaster	Benign	1.0	D;D
PROVEAN	Uncertain	-2.7	D;D
REVEL	Pathogenic	0.76
Sift	Benign	0.057	T;T
Sift4G	Benign	0.090	T;T
Polyphen		0.86	P;D
Vest4		0.66
MutPred		0.78		Loss of helix (P = 0.0167);Loss of helix (P = 0.0167);
MVP		1.0
MPC		0.75
ClinPred		0.91	D
GERP RS		4.9
Varity_R		0.19
gMVP		0.78

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: rs28937887; hg19: chr10-102748968;