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Heteroplasmy

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Heteroplasmy is the co-existence of multiple mitochondrial DNA variants in a single source. There are multiple copies of mtDNA in each cell. Heteroplasmy is the name given to denote mutations which affect only a proportion of the molecules in a cell. The term homoplasmy is used to describe mutations which affect all of the molecules.

The level of heteroplasmy can vary between cells in the same tissue or organ, from organ to organ within the same person, and between individuals in the same family. Low levels of heteroplasmy have been found in almost every healthy individual who has been studied to date. MtDNA mutations that have occurred within approximately three human generations are usually heteroplasmic. Animal research has suggested that de novo heteroplasmic mutations become fixed and homoplasmic within two or three generations.[1]

If you have taken a mitochondrial DNA test you will know that you have a heteroplasmy from the letter codes used to describe the positions in your mtDNA sequence. Non-heteroplasmic positions are followed by the letters A, C, T or G (the letters which denote the base pairs). Heteroplasmic positions will carry one of the following letters: U, M, R, W, H, D or N. The letter code used determines the nature of the heteroplasmy.[2]

Length heteroplasmy vs. sequence heteroplasmy

Sequence heteroplasmy involves the coexistence of two strains of DNA that differ at a single nucleotide or SNP. For example:

Strain 1:
...AGTCTGGATTC...
Strain 2:
...AGTCTAGATTC...

Length heteroplasmy involves the coexistence of two strains of DNA that have different lengths for tracts of repeated nucleotides. For example:

Strain 1:
...TGAATCCCCCCCCCTTGAA...
Strain 2:
...TGAATCCCCCCCCCCCTTGAA...


Notable cases

A notable example of heteroplasmy was seen in the case of Nicholas II of Russia. His heteroplasmy, and that of his brother, served to convince Russian authorities of the authenticity of his remains.[3],[4]

FTDNA Learning Center articles

Further reading

Scientific papers

Tools

References

  1. Stewart JB, Chinnery PF (2015). The dynamics of mitochondrial DNA heteroplasmy: implications for human health and disease (£). Nature Reviews Genetics 535: 530-542.
  2. How do I know if I have a mitchondrial DNA heteroplasmy? What is the nomenclature?
  3. Ivanov PL, Wadhams MJ, Roby RK, Holland MM, Weedn VW, Parsons TJ. Mitochondrial DNA sequence heteroplasmy in the Grand Duke of Russia Georgij Romanov establishes the authenticity of the remains of Tsar Nicholas II. Nat. Genet. April 1996, Volume 12, Issue 4. pp417–20 7
  4. Michael D. Coble, Odile M. Loreille, Mark J. Wadhams et al. Mystery Solved: The Identification of the Two Missing Romanov Children Using DNA Analysis. PLoS One' 2009 Volume 4, number 3, p34838.

See also