Heteroplasmy is the presence of a mixture of more than one type of an organellar
In cell biology, an organelle is a specialized subunit within a cell that has a specific function, and is usually separately enclosed within its own lipid bilayer....

In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....

 (mitochondrial DNA
Mitochondrial DNA
Mitochondrial DNA is the DNA located in organelles called mitochondria, structures within eukaryotic cells that convert the chemical energy from food into a form that cells can use, adenosine triphosphate...

 (mtDNA) or plastid
Plastids are major organelles found in the cells of plants and algae. Plastids are the site of manufacture and storage of important chemical compounds used by the cell...

 DNA) within a cell or individual. It is a factor for the severity of mitochondrial disease
Mitochondrial disease
Mitochondrial diseases are a group of disorders caused by dysfunctional mitochondria, the organelles that are the "powerhouses" of the cell. Mitochondria are found in every cell of the human body except red blood cells...

s, since most eukaryotic cells contains many hundreds of mitochondria with hundreds of copies of mtDNA, it is possible and indeed very frequent for mutation
In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...

s to affect only some of the copies, while the remaining ones are unaffected.

Symptoms of severe heteroplasmic mitochondrial disorders frequently do not appear until adulthood because many cell divisions and a lot of time is required for a cell to receive enough mitochondria containing the mutant alleles to cause symptoms. An example of this phenomenon is Leber optic atrophy
Leber's hereditary optic neuropathy
Leber’s hereditary optic neuropathy or Leber optic atrophy is a mitochondrially inherited degeneration of retinal ganglion cells and their axons that leads to an acute or subacute loss of central vision; this affects predominantly young adult males...

. Individuals with this condition often do not experience vision difficulties until they have reached adulthood. Another example is MERRF syndrome
MERRF syndrome
MERRF syndrome is a mitochondrial disease. It is extremely rare, with an estimated prevalence of 1/400,000 in Europe, and has varying degrees of expressivity owing to heteroplasmy-Presentation:...

 (or Myoclonic Epilepsy with Ragged Red Fibers). In MELAS, heteroplasmy explains the variation in severity of the disease among siblings.

Notable cases

One notable example of an otherwise healthy individual whose heteroplasmy was discovered incidentally is Nicholas II of Russia
Nicholas II of Russia
Nicholas II was the last Emperor of Russia, Grand Prince of Finland, and titular King of Poland. His official short title was Nicholas II, Emperor and Autocrat of All the Russias and he is known as Saint Nicholas the Passion-Bearer by the Russian Orthodox Church.Nicholas II ruled from 1894 until...

, whose heteroplasmy (and that of his brother) served to convince Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...

n authorities of the authenticity of his remains.

See also

  • homoplasmy
    Homoplasmy is the presence of a mutation affecting all of the mitochondrial DNA copies in a mammalian cell or chloroplast DNA in a plant cell. However, when a mutation occurs, it only affects some of the mitochondria, but not all of them known as heteroplasmy...

  • microheteroplasmy
    In biology, microheteroplasmy is a form of heteroplasmy, a type of mutational damage to mitochondrial DNA. While heteroplasmy in general includes mutations present in any fraction of mtDNA , microheteroplasmy is the presence of mutations levels of up to about 2−5%...

  • Paternal mtDNA transmission
    Paternal mtDNA transmission
    In genetics, paternal mtDNA transmission and paternal mtDNA inheritance refer to the incidence of mitochondrial DNA being passed from a father to his offspring. Paternal mtDNA inheritance is observed in a small proportion of species; in general, mtDNA is passed unchanged from a mother to her...

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