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# Mitochondrial inheritance and mitochondrial DNA disease

Mitochondria carry their own small genome, passed only from the mother; how much faulty mtDNA a tissue holds decides whether and how disease appears.

Updated Nov 13, 2026

## Key facts

- Mitochondrial DNA is a circle of about 16 600 base pairs with 37 genes: 13 proteins of the respiratory chain, 22 transfer RNAs and 2 ribosomal RNAs. Each cell holds hundreds to thousands of copies.
- It is inherited from the mother only; an affected man does not pass mtDNA disease to his children.
- Heteroplasmy: a cell can hold a mix of normal and mutant mtDNA. Disease appears when the mutant share passes a tissue's threshold.
- A bottleneck in egg development means a mother's children can receive very different mutant loads, so recurrence risk is hard to predict.
- Most mitochondrial proteins are encoded in the nucleus, so many «mitochondrial diseases» follow Mendelian inheritance (for example POLG and SURF1 defects).

## In detail

- Tissues with the highest energy needs suffer most: brain, skeletal and heart muscle, retina, inner ear, kidney tubules and pancreatic islets.
- Classic mtDNA disorders: MELAS (stroke-like episodes, lactic acidosis), MERRF (myoclonic epilepsy, ragged-red fibres), Leber hereditary optic neuropathy (painless loss of central vision, mostly in young men), Kearns–Sayre syndrome (usually a sporadic large deletion) and maternally inherited Leigh syndrome.
- The mutant load in blood can be lower than in muscle or urine, so the right sample matters when testing.
- Mitochondrial donation during IVF can prevent transmission of mtDNA disease and is permitted in a few countries.

**Also called**
Maternal inheritance, Heteroplasmy and the threshold effect

## Clinical notes

- Suspect a mitochondrial disorder when several unrelated organs fail together, with lactic acidosis, deafness, diabetes or short stature, especially along the maternal line.
- Valproate can cause liver failure in POLG-related disease.

## Test yourself

Think of the answer, then tap the question to see it.

## Why can an affected father not transmit an mtDNA disease?

Mitochondria in the embryo come from the egg; sperm mitochondria are eliminated after fertilisation.

## What is heteroplasmy, and why does it matter?

A mix of normal and mutant mtDNA in a cell; disease appears only when the mutant share exceeds the tissue's threshold.

## Why are many mitochondrial diseases inherited in a Mendelian way?

Most mitochondrial proteins are encoded by nuclear genes.

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## Connections

## Related conditions 3

- [MELAS (mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes)](https://durgical.com/en/conditions/melas/)
- [Leigh syndrome](https://durgical.com/en/conditions/leigh-syndrome/)
- [Leber hereditary optic neuropathy (LHON)](https://durgical.com/en/conditions/leber-hereditary-optic-neuropathy/)

## Related 4

- [Electron transport chain and oxidative phosphorylation](https://durgical.com/en/biochemistry/pathways/electron-transport-chain-and-oxidative-phosphorylation/)
- [Transfer RNA (tRNA)](https://durgical.com/en/biochemistry/topics/transfer-rna/)
- [Where new mutations come from: de novo variants, rates and parental age](https://durgical.com/en/biochemistry/topics/where-new-mutations-come-from-de-novo-variants-rates-and-parental-age/)
- [Inheritance concepts, genotype–phenotype and the pedigree](https://durgical.com/en/biochemistry/topics/inheritance-concepts-genotype-phenotype-and-the-pedigree/)

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Mitochondrial DNA: MedlinePlus Genetics](https://medlineplus.gov/genetics/chromosome/mitochondrial-dna/) (MedlinePlus, US National Library of Medicine, 2026); [Mitochondrial DNA](https://www.genome.gov/genetics-glossary/Mitochondrial-DNA) (National Human Genome Research Institute (NHGRI), 2026).

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/biochemistry/topics/mitochondrial-inheritance-and-mitochondrial-dna-disease/