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Genetics Home Reference: your guide to understanding genetic conditions     A service of the U.S. National Library of Medicine®


Reviewed September 2013

What is the official name of the TK2 gene?

The official name of this gene is “thymidine kinase 2, mitochondrial.”

TK2 is the gene's official symbol. The TK2 gene is also known by other names, listed below.

What is the normal function of the TK2 gene?

The TK2 gene provides instructions for making an enzyme called thymidine kinase 2 that functions within cell structures called mitochondria, which are found in all tissues. Mitochondria are involved in a wide variety of cellular activities, including energy production; chemical signaling; and regulation of cell growth, cell division, and cell death. Mitochondria contain their own genetic material, known as mitochondrial DNA (mtDNA), which is essential for the normal function of these structures. Thymidine kinase 2 is involved in the production and maintenance of mtDNA. Specifically, this enzyme plays a role in recycling mtDNA building blocks (nucleotides) so that errors in mtDNA sequencing can be repaired and new mtDNA molecules can be produced.

How are changes in the TK2 gene related to health conditions?

TK2-related mitochondrial DNA depletion syndrome, myopathic form - caused by mutations in the TK2 gene

More than 30 mutations in the TK2 gene have been found to cause TK2-related mitochondrial DNA depletion syndrome, myopathic form (TK2-MDS). TK2-MDS is an inherited condition that causes progressive muscle weakness (myopathy), typically beginning in early childhood. About two-thirds of the mutations that cause this condition change single protein building blocks (amino acids) in thymidine kinase 2. All TK2 gene mutations result in a decrease of enzyme activity, which impairs recycling of mtDNA nucleotides. A shortage of nucleotides available for the repair and production of mtDNA molecules leads to a reduction in the amount of mtDNA (known as mtDNA depletion) and impairs mitochondrial function. Greater mtDNA depletion tends to cause more severe signs and symptoms. The muscle cells of people with TK2-MDS have very low amounts of mtDNA, ranging from 5 to 30 percent of normal. Other tissues can have 60 percent of normal to normal amounts of mtDNA. The cause for the variability in the amount of mtDNA lost among affected individuals, even those with the same mutations, is unknown.

It is unclear why TK2 gene mutations typically affect only muscle tissue, but the high energy demands of muscle cells may make them the most susceptible to cell death when mtDNA is lost and less energy is produced in cells.

Where is the TK2 gene located?

Cytogenetic Location: 16q22-q23.1

Molecular Location on chromosome 16: base pairs 66,508,003 to 66,550,412

(Homo sapiens Annotation Release 107, GRCh38.p2) (NCBI (

The TK2 gene is located on the long (q) arm of chromosome 16 between positions 22 and 23.1.

The TK2 gene is located on the long (q) arm of chromosome 16 between positions 22 and 23.1.

More precisely, the TK2 gene is located from base pair 66,508,003 to base pair 66,550,412 on chromosome 16.

See How do geneticists indicate the location of a gene? ( in the Handbook.

Where can I find additional information about TK2?

You and your healthcare professional may find the following resources about TK2 helpful.

You may also be interested in these resources, which are designed for genetics professionals and researchers.

What other names do people use for the TK2 gene or gene products?

  • MTDPS2
  • MTTK
  • mt-TK

See How are genetic conditions and genes named? ( in the Handbook.

What glossary definitions help with understanding TK2?

acids ; cell ; cell division ; depletion ; DNA ; enzyme ; gene ; inherited ; kinase ; mitochondria ; muscle cells ; nucleoside ; protein ; sequencing ; syndrome ; tissue

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.


  • Blakely E, He L, Gardner JL, Hudson G, Walter J, Hughes I, Turnbull DM, Taylor RW. Novel mutations in the TK2 gene associated with fatal mitochondrial DNA depletion myopathy. Neuromuscul Disord. 2008 Jul;18(7):557-60. doi: 10.1016/j.nmd.2008.04.014. Epub 2008 May 27. (
  • Eriksson S, Wang L. Molecular mechanisms of mitochondrial DNA depletion diseases caused by deficiencies in enzymes in purine and pyrimidine metabolism. Nucleosides Nucleotides Nucleic Acids. 2008 Jun;27(6):800-8. doi: 10.1080/15257770802146197. Review. (
  • Galbiati S, Bordoni A, Papadimitriou D, Toscano A, Rodolico C, Katsarou E, Sciacco M, Garufi A, Prelle A, Aguennouz M', Bonsignore M, Crimi M, Martinuzzi A, Bresolin N, Papadimitriou A, Comi GP. New mutations in TK2 gene associated with mitochondrial DNA depletion. Pediatr Neurol. 2006 Mar;34(3):177-85. (
  • Götz A, Isohanni P, Pihko H, Paetau A, Herva R, Saarenpää-Heikkilä O, Valanne L, Marjavaara S, Suomalainen A. Thymidine kinase 2 defects can cause multi-tissue mtDNA depletion syndrome. Brain. 2008 Nov;131(Pt 11):2841-50. doi: 10.1093/brain/awn236. Epub 2008 Sep 26. (
  • Munch-Petersen B. Enzymatic regulation of cytosolic thymidine kinase 1 and mitochondrial thymidine kinase 2: a mini review. Nucleosides Nucleotides Nucleic Acids. 2010 Jun;29(4-6):363-9. doi: 10.1080/15257771003729591. Review. (
  • NCBI Gene (


The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? ( in the Handbook.

Reviewed: September 2013
Published: February 1, 2016