rs281865494

Variant names:

• chr16-66529027-G-A
• rs281865494
• NM_004614.5:c.416C>T

Your query was ambiguous. Multiple possible variants found:

• chr16-66529027-G-A
• chr16-66529027-G-C

Variant summary

Our verdict is Pathogenic. The variant received 15 ACMG points: 15P and 0B. PM1 PM2 PM5 PP3 PP5_Very_Strong

The NM_004614.5(TK2):​c.416C>T​(p.Ala139Val) variant causes a missense change. The variant allele was found at a frequency of 0.0000483 in 1,613,916 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 (★★). Another variant affecting the same amino acid position, but resulting in a different missense (i.e. A139S) has been classified as Likely pathogenic.

• Frequency:
  • Genomes: 𝑓 0.000072 (0 hom., cov: 33)
  • Exomes 𝑓: 0.000046 (0 hom.)
• Consequence: TK2 NM_004614.5 missense
• Clinical Significance: Pathogenic/Likely pathogenic criteria provided, multiple submitters, no conflicts P:11 O:1
• Conservation: PhyloP100: 5.63
• Publications: 10 publications found

Genes affected

TK2 (HGNC:11831): (thymidine kinase 2) This gene encodes a deoxyribonucleoside kinase that specifically phosphorylates thymidine, deoxycytidine, and deoxyuridine. The encoded enzyme localizes to the mitochondria and is required for mitochondrial DNA synthesis. Mutations in this gene are associated with a myopathic form of mitochondrial DNA depletion syndrome. Alternate splicing results in multiple transcript variants encoding distinct isoforms, some of which lack transit peptide, so are not localized to mitochondria. [provided by RefSeq, Dec 2012]

TK2 Gene-Disease associations (from GenCC):

• mitochondrial disease

  Inheritance: AR Classification: DEFINITIVE Submitted by: ClinGen
• mitochondrial DNA depletion syndrome, myopathic form

  Inheritance: AR Classification: DEFINITIVE, STRONG, SUPPORTIVE Submitted by: Orphanet, G2P, Labcorp Genetics (formerly Invitae)
• autosomal recessive progressive external ophthalmoplegia

  Inheritance: AR Classification: SUPPORTIVE Submitted by: Orphanet

ACMG classification

Our verdict: Pathogenic. The variant received 15 ACMG points.

• PM1: In a hotspot region, there are 10 aminoacids with missense pathogenic changes in the window of +-8 aminoacids around while only 0 benign, 5 uncertain in NM_004614.5
• PM2: Very rare variant in population databases, with high coverage
• PM5: Other missense variant is known to change same aminoacid residue: Variant chr16-66529028-C-A is described in ClinVar as Conflicting_classifications_of_pathogenicity. ClinVar VariationId is 808055.
• PP3: Splicing predictors support a deleterious effect. Scorers claiming Pathogenic: max_spliceai. No scorers claiming Uncertain. No scorers claiming Benign.
• PP5: Variant 16-66529027-G-A is Pathogenic according to our data. Variant chr16-66529027-G-A is described in ClinVar as Pathogenic/Likely_pathogenic. ClinVar VariationId is 38990.Status of the report is criteria_provided_multiple_submitters_no_conflicts, 2 stars.

Variant Effect in Transcripts

ACMG analysis was done for transcript: NM_004614.5. You can select a different transcript below to see updated ACMG assignments.

RefSeq Transcripts

Selected	Gene	Transcript	Tags	HGVSc	HGVSp	Effect	Exon Rank	Protein	UniProt
	TK2	NM_004614.5	MANE Select	c.416C>T	p.Ala139Val	missense	Exon 6 of 10	NP_004605.4
	TK2	NM_001172645.2		c.362C>T	p.Ala121Val	missense	Exon 5 of 9	NP_001166116.1
	TK2	NM_001172644.2		c.341C>T	p.Ala114Val	missense	Exon 5 of 9	NP_001166115.1

Ensembl Transcripts

Selected	Gene	Transcript	Tags	HGVSc	HGVSp	Effect	Exon Rank	Protein	UniProt
	TK2	ENST00000544898.6	TSL:1 MANE Select	c.416C>T	p.Ala139Val	missense	Exon 6 of 10	ENSP00000440898.2
	TK2	ENST00000451102.7	TSL:1	c.323C>T	p.Ala108Val	missense	Exon 6 of 10	ENSP00000414334.4
	TK2	ENST00000527284.6	TSL:1	c.359C>T	p.Ala120Val	missense	Exon 6 of 9	ENSP00000435312.2

Frequencies

GnomAD3 genomes AF: 0.0000723 AC: 11 AN: 152122 Hom.: 0 Cov.: 33

Gnomad AFR AF: 0.00

Gnomad AMI AF: 0.00

Gnomad AMR AF: 0.000131

Gnomad ASJ AF: 0.00

Gnomad EAS AF: 0.00

Gnomad SAS AF: 0.00

Gnomad FIN AF: 0.00

Gnomad MID AF: 0.00

Gnomad NFE AF: 0.000132

Gnomad OTH AF: 0.00

GnomAD2 exomes AF: 0.0000278 AC: 7 AN: 251356 AF XY: 0.0000147

Gnomad AFR exome AF: 0.00

Gnomad AMR exome AF: 0.0000289

Gnomad ASJ exome AF: 0.00

Gnomad EAS exome AF: 0.00

Gnomad FIN exome AF: 0.00

Gnomad NFE exome AF: 0.0000440

Gnomad OTH exome AF: 0.000163

GnomAD4 exome AF: 0.0000458 AC: 67 AN: 1461794 Hom.: 0 Cov.: 31 AF XY: 0.0000509 AC XY: 37 AN XY: 727210

African (AFR) AF: 0.00 AC: 0 AN: 33480

American (AMR) AF: 0.0000447 AC: 2 AN: 44724

Ashkenazi Jewish (ASJ) AF: 0.00 AC: 0 AN: 26136

East Asian (EAS) AF: 0.00 AC: 0 AN: 39700

South Asian (SAS) AF: 0.00 AC: 0 AN: 86256

European-Finnish (FIN) AF: 0.00 AC: 0 AN: 53336

Middle Eastern (MID) AF: 0.00 AC: 0 AN: 5768

European-Non Finnish (NFE) AF: 0.0000558 AC: 62 AN: 1111998

Other (OTH) AF: 0.0000497 AC: 3 AN: 60396

GnomAD4 genome AF: 0.0000723 AC: 11 AN: 152122 Hom.: 0 Cov.: 33 AF XY: 0.0000404 AC XY: 3 AN XY: 74306

African (AFR) AF: 0.00 AC: 0 AN: 41404

American (AMR) AF: 0.000131 AC: 2 AN: 15274

Ashkenazi Jewish (ASJ) AF: 0.00 AC: 0 AN: 3472

East Asian (EAS) AF: 0.00 AC: 0 AN: 5200

South Asian (SAS) AF: 0.00 AC: 0 AN: 4826

European-Finnish (FIN) AF: 0.00 AC: 0 AN: 10598

Middle Eastern (MID) AF: 0.00 AC: 0 AN: 316

European-Non Finnish (NFE) AF: 0.000132 AC: 9 AN: 68028

Other (OTH) AF: 0.00 AC: 0 AN: 2092

Alfa AF: 0.0000986 Hom.: 0

Bravo AF: 0.0000831

ExAC AF: 0.00000824 AC: 1

EpiCase AF: 0.000109

EpiControl AF: 0.0000593

ClinVar

Significance: Pathogenic/Likely pathogenic

Submissions summary: Pathogenic:11 Other:1

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

not provided Pathogenic:6 Other:1

Oct 01, 2024

CeGaT Center for Human Genetics Tuebingen

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

TK2: PM3:Very Strong, PM1, PM2, PM5, PP3

Genome Diagnostics Laboratory, Amsterdam University Medical Center

Significance: Likely pathogenic

Review Status: no assertion criteria provided

Collection Method: clinical testing

GenomeConnect, ClinGen

Significance: not provided

Review Status: no classification provided

Collection Method: phenotyping only

Variant classified as not provided and reported on 03-12-2021 by GeneDx. GenomeConnect assertions are reported exactly as they appear on the patient-provided report from the testing laboratory. GenomeConnect staff make no attempt to reinterpret the clinical significance of the variant.

Feb 19, 2021

GeneDx

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

Quantitative PCR analysis demonstrates marked depletion of mtDNA copy numbers in skeletal muscle from affected individuals (Knierim et al., 2015).; Not observed at a significant frequency in large population cohorts (Lek et al., 2016); In silico analysis, which includes splice predictors and evolutionary conservation, suggests this variant may impact gene splicing. In the absence of RNA/functional studies, the actual effect of this sequence change is unknown.; In silico analysis supports that this missense variant has a deleterious effect on protein structure/function; This variant is associated with the following publications: (PMID: 30609409, 29602790, 25446393, 27839525, 16504786)

Jul 27, 2023

Revvity Omics, Revvity

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

Diagnostic Laboratory, Department of Genetics, University Medical Center Groningen

Significance: Pathogenic

Review Status: no assertion criteria provided

Collection Method: clinical testing

Jul 24, 2024

Labcorp Genetics (formerly Invitae), Labcorp

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

This sequence change replaces alanine, which is neutral and non-polar, with valine, which is neutral and non-polar, at codon 139 of the TK2 protein (p.Ala139Val). This variant is present in population databases (rs281865494, gnomAD 0.004%). This missense change has been observed in individual(s) with mitochondrial DNA depletion syndrome (PMID: 16504786, 25446393). It has also been observed to segregate with disease in related individuals. This variant is also known as A181V. ClinVar contains an entry for this variant (Variation ID: 38990). 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 TK2 protein function with a negative predictive value of 80%. Algorithms developed to predict the effect of sequence changes on RNA splicing suggest that this variant may create or strengthen a splice site. For these reasons, this variant has been classified as Pathogenic.

Mitochondrial DNA depletion syndrome Pathogenic:2

Sep 21, 2017

Laboratory for Molecular Medicine, Mass General Brigham Personalized Medicine

Significance: Likely pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

The p.Ala139Val (NM_004614.4 c.416C>T) (also referred to as p.Ala181Val in the l iterature) variant in TK2 has been reported in one compound heterozygous and one homozygous patients with mitochondrial DNA depletion syndrome and segregated in two affected siblings from two families (Galbiati 2006 and Knierim 2015). This variant has also been reported in ClinVar (Variation ID#5782). It has been ident ified in 5/126,712 of European chromosomes by the Genome Aggregation Database (g nomAD, http://gnomad.broadinstitute.org; dbSNP rs281865494). Although this varia nt has been seen in the general population, its frequency is low enough to be co nsistent with a recessive carrier frequency. Computational prediction tools and conservation analysis suggest that the p.Ala139Val variant may impact the protei n, though this information is not predictive enough to determine pathogenicity. In summary, although additional studies are required to fully establish its clin ical significance, the p.Ala139Val variant is likely pathogenic for TK2-related mitochondrial DNA depletion syndrome in an autosomal recessive manner based on i ts occurrence in individuals with this disease and low frequency in the general population.

Dec 14, 2022

Women's Health and Genetics/Laboratory Corporation of America, LabCorp

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

Variant summary: TK2 c.416C>T (p.Ala139Val) results in a non-conservative amino acid change located in the Deoxynucleoside kinase domain (IPR031314) of the encoded protein sequence. Five of five in-silico tools predict a damaging effect of the variant on protein function. The variant allele was found at a frequency of 2.8e-05 in 251356 control chromosomes (gnomAD). c.416C>T has been reported in the literature in multiple homozygous and compound heterozygous individuals affected with Mitochondrial DNA Depletion Syndrome - TK2 Related, and segregated with disease within families (e.g. Galbiati_2006, Knierim_2015, Wahbi_2015, Mazurova_2017). These data indicate that the variant is very likely to be associated with disease. Four ClinVar submitters (evaluation after 2014) cite the variant as pathogenic/likely pathogenic. Based on the evidence outlined above, the variant was classified as pathogenic.

Mitochondrial disease Pathogenic:1

Apr 10, 2025

Genomenon, Inc, Genomenon, Inc

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: curation

TK2 Ala139Val (c.416C>T) is a missense variant that changes the amino acid at residue 139 from Alanine to Valine. It is also described as A181V in the literature. This variant has been observed in multiple probands affected with mitochondrial disease in both the homozygous and compound heterozygous state (PMID:16504786;27839525;32904881;25446393). TK2 Ala139Val was found to segregate with disease in multiple affected families (PMID:16504786;25446393). This variant is not present at a significant frequency in gnomAD and in silico models agree that this variant is possibly or probably damaging. In conclusion, we classify TK2 Ala139Val (c.416C>T) as a pathogenic variant.

TK2-related disorder Pathogenic:1

Oct 28, 2023

PreventionGenetics, part of Exact Sciences

Significance: Pathogenic

Review Status: no assertion criteria provided

Collection Method: clinical testing

The TK2 c.416C>T variant is predicted to result in the amino acid substitution p.Ala139Val. This variant has been reported in individuals with autosomal recessive mitochondrial DNA depletion syndrome (referred to as c.542C>T, p.Ala181Val, Fig 3b, Galbiati et al. 2006. PubMed ID: 16504786; Knierim et al. 2014. PubMed ID: 25446393; Mazurova et al. 2016. PubMed ID: 27839525; Figure 2, Garone et al. 2018. PubMed ID: 29602790; Table S3, Ganapathy et al. 2019. PubMed ID: 31069529; Papadimas et al. 2020. PubMed ID: 32904881). This variant is reported in 0.0046% of alleles in individuals of European (Non-Finnish) descent in gnomAD (http://gnomad.broadinstitute.org/variant/16-66562930-G-A). This variant is interpreted as pathogenic.

Mitochondrial DNA depletion syndrome, myopathic form;C4310734:Progressive external ophthalmoplegia with mitochondrial DNA deletions, autosomal recessive 3 Pathogenic:1

Oct 31, 2018

Fulgent Genetics, Fulgent Genetics

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

Computational scores

Source: dbNSFP v4.9

Name	Calibrated prediction	Score	Prediction
AlphaMissense	Pathogenic	0.71
BayesDel_addAF	Pathogenic	0.46	D
BayesDel_noAF	Pathogenic	0.53
CADD	Pathogenic	35
DANN	Pathogenic	1.0
DEOGEN2	Pathogenic	0.95	D
Eigen	Pathogenic	0.76
Eigen_PC	Pathogenic	0.75
FATHMM_MKL	Uncertain	0.96	D
LIST_S2	Pathogenic	0.98	D
M_CAP	Pathogenic	0.41	D
MetaRNN	Pathogenic	0.91	D
MetaSVM	Pathogenic	1.1	D
MutationAssessor	Pathogenic	3.1	M
PhyloP100		5.6
PrimateAI	Uncertain	0.54	T
PROVEAN	Uncertain	-3.7	D
REVEL	Pathogenic	0.91
Sift	Uncertain	0.0050	D
Sift4G	Uncertain	0.010	D
Polyphen		1.0	D
Vest4		0.96
MVP		0.99
MPC		1.1
ClinPred		0.91	D
GERP RS		5.6
RBP_binding_hub_radar		0.0
RBP_regulation_power_radar		1.7
Varity_R		0.83
gMVP		0.88
Mutation Taster		=0/100	disease causing (ClinVar)

Splicing

Name	Calibrated prediction	Score	Prediction
Splicevardb		2.0
SpliceAI score (max)		0.66		Details are displayed if max score is > 0.2
DS_DG_spliceai		0.66		Position offset: 2

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

Other links and lift over

dbSNP: rs281865494; hg19: chr16-66562930;