NM_004614.5:c.156+2T>C

Variant names:

• chr16-66548976-A-G
• rs281865499
• NM_004614.5:c.156+2T>C

Variant summary

Our verdict is Pathogenic. The variant received 18 ACMG points: 18P and 0B. PVS1 PM2 PP5_Very_Strong

The NM_004614.5(TK2):​c.156+2T>C variant causes a splice donor, intron change. The variant allele was found at a frequency of 0.0000155 in 1,612,962 control chromosomes in the GnomAD database, with no homozygous occurrence. In-silico tool predicts a pathogenic outcome for this variant. 2/3 splice prediction tools predicting alterations to normal splicing. Variant has been reported in ClinVar as Likely pathogenic (★★).

• Frequency:
  • Genomes: 𝑓 0.000033 (0 hom., cov: 32)
  • Exomes 𝑓: 0.000014 (0 hom.)
• Consequence: TK2 NM_004614.5 splice_donor, intron
• Scores: Splicing: ADA: 0.9909
• Clinical Significance: Pathogenic/Likely pathogenic criteria provided, multiple submitters, no conflicts P:4
• Conservation: PhyloP100: 3.75
• Publications: 2 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 18 ACMG points.

• PVS1: Splicing +-2 bp (donor or acceptor) variant, LoF is a know mechanism of disease, No cryptic splice site detected. Exon removal results in frameshift change.
• PM2: Very rare variant in population databases, with high coverage
• PP5: Variant 16-66548976-A-G is Pathogenic according to our data. Variant chr16-66548976-A-G is described in ClinVar as [Likely_pathogenic]. Clinvar id is 38977.Status of the report is criteria_provided_multiple_submitters_no_conflicts, 2 stars.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	MANE	Protein	UniProt
TK2	NM_004614.5	c.156+2T>C		splice_donor_variant, intron_variant	Intron 2 of 9	ENST00000544898.6	NP_004605.4

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	TSL	MANE	Protein	Appris	UniProt
TK2	ENST00000544898.6	c.156+2T>C		splice_donor_variant, intron_variant	Intron 2 of 9	1	NM_004614.5	ENSP00000440898.2

Frequencies

GnomAD3 genomes AF: 0.0000328 AC: 5 AN: 152220 Hom.: 0 Cov.: 32

Gnomad AFR AF: 0.00

Gnomad AMI AF: 0.00

Gnomad AMR AF: 0.00

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: 0.0000588

Gnomad OTH AF: 0.000478

GnomAD2 exomes AF: 0.0000159 AC: 4 AN: 251356 AF XY: 0.0000294

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 FIN exome AF: 0.00

Gnomad NFE exome AF: 0.0000352

Gnomad OTH exome AF: 0.00

GnomAD4 exome AF: 0.0000137 AC: 20 AN: 1460624 Hom.: 0 Cov.: 30 AF XY: 0.0000138 AC XY: 10 AN XY: 726750

African (AFR) AF: 0.00 AC: 0 AN: 33444

American (AMR) AF: 0.00 AC: 0 AN: 44710

Ashkenazi Jewish (ASJ) AF: 0.00 AC: 0 AN: 26118

East Asian (EAS) AF: 0.00 AC: 0 AN: 39682

South Asian (SAS) AF: 0.00 AC: 0 AN: 86236

European-Finnish (FIN) AF: 0.00 AC: 0 AN: 53402

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

European-Non Finnish (NFE) AF: 0.0000171 AC: 19 AN: 1110934

Other (OTH) AF: 0.0000166 AC: 1 AN: 60330

GnomAD4 genome AF: 0.0000328 AC: 5 AN: 152338 Hom.: 0 Cov.: 32 AF XY: 0.0000403 AC XY: 3 AN XY: 74488

African (AFR) AF: 0.00 AC: 0 AN: 41574

American (AMR) AF: 0.00 AC: 0 AN: 15298

Ashkenazi Jewish (ASJ) AF: 0.00 AC: 0 AN: 3470

East Asian (EAS) AF: 0.00 AC: 0 AN: 5190

South Asian (SAS) AF: 0.00 AC: 0 AN: 4832

European-Finnish (FIN) AF: 0.00 AC: 0 AN: 10626

Middle Eastern (MID) AF: 0.00 AC: 0 AN: 294

European-Non Finnish (NFE) AF: 0.0000588 AC: 4 AN: 68026

Other (OTH) AF: 0.000473 AC: 1 AN: 2116

Alfa AF: 0.0000268 Hom.: 0

Bravo AF: 0.0000340

TwinsUK AF: 0.00 AC: 0

ALSPAC AF: 0.000259 AC: 1

ExAC AF: 0.0000247 AC: 3

ClinVar

Significance: Pathogenic/Likely pathogenic

Submissions summary: Pathogenic:4

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

not provided Pathogenic:2

Dec 03, 2024

Labcorp Genetics (formerly Invitae), Labcorp

Significance: Likely pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

This sequence change affects a donor splice site in intron 2 of the TK2 gene. It is expected to disrupt RNA splicing. Variants that disrupt the donor or acceptor splice site typically lead to a loss of protein function (PMID: 16199547), and loss-of-function variants in TK2 are known to be pathogenic (PMID: 20421844). This variant is present in population databases (rs281865499, gnomAD 0.004%). Disruption of this splice site has been observed in individual(s) with mitochondrial DNA depletion syndrome (PMID: 19748572). This variant is also known as c.282+2T>C. ClinVar contains an entry for this variant (Variation ID: 38977). Algorithms developed to predict the effect of sequence changes on RNA splicing suggest that this variant may disrupt the consensus splice site. 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. -

Dec 04, 2024

GeneDx

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

Previously reported as pathogenic variant; no clinical or segregation information was reported (PMID: 19748572); Canonical splice site variant predicted to result in a null allele in a gene for which loss of function is a known mechanism of disease; Not observed at significant frequency in large population cohorts (gnomAD); Also known as c.282+2T>C; This variant is associated with the following publications: (PMID: 25525159, 19748572) -

Mitochondrial disease Pathogenic:1

Apr 10, 2025

Genomenon, Inc, Genomenon, Inc

Significance: Likely pathogenic

Review Status: criteria provided, single submitter

Collection Method: curation

TK2 c.156+2T>C is a canonical splice variant located in the donor splice region of intron 2. It is predicted to affect mRNA splicing, leading to a deleterious effect on the TK2 protein. It is also described as c.282+2T>C in the literature. Patient(s) have been reported without clinical or zygosity information (PMID:19748572). This variant is not present at a significant frequency in gnomAD. In conclusion, we classify TK2 c.156+2T>C as a likely pathogenic variant. -

Mitochondrial DNA depletion syndrome Pathogenic:1

Dec 13, 2023

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

Significance: Likely pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

Variant summary: TK2 c.156+2T>C is located in a canonical splice-site and is predicted to affect mRNA splicing resulting in a significantly altered protein due to either exon skipping, shortening, or inclusion of intronic material. Several computational tools predict a significant impact on normal splicing: Three predict the variant abolishes the 5' canonical splicing donor site. One predict the variant no significant impact on splicing. However, these predictions have yet to be confirmed by functional studies. The variant allele was found at a frequency of 1.6e-05 in 251356 control chromosomes. c.156+2T>C has been reported in the literature in unspecified individual(s) affected with Mitochondrial DNA Depletion Syndrome - TK2 Related (example, Poulton_2009). Detailed individual information was not however provided for an independent analysis. To our knowledge, no experimental evidence demonstrating an impact on protein function has been reported. The following publication have been ascertained in the context of this evaluation (PMID: 19748572). Two submitters have cited clinical-significance assessments for this variant to ClinVar after 2014. Both submitters classified the variant as pathogenic/likely pathogenic. Based on the evidence outlined above, the variant was classified as likely pathogenic. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
BayesDel_addAF	Pathogenic	0.53	D
BayesDel_noAF	Pathogenic	0.14
CADD	Pathogenic	26
DANN	Uncertain	0.98
Eigen	Pathogenic	0.94
Eigen_PC	Pathogenic	0.75
FATHMM_MKL	Uncertain	0.84	D
PhyloP100		3.7
GERP RS		4.2
PromoterAI		-0.023	Neutral
RBP_binding_hub_radar		0.0
RBP_regulation_power_radar		2.8
Mutation Taster		=0/100	disease causing (ClinVar)

Splicing

Name	Calibrated prediction	Score	Prediction
dbscSNV1_ADA	Pathogenic	0.99
dbscSNV1_RF	Benign	0.63
SpliceAI score (max)		0.97		Details are displayed if max score is > 0.2
DS_DL_spliceai		0.97		Position offset: 2

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

Other links and lift over

dbSNP: rs281865499; hg19: chr16-66582879;