Mitochondria: Powerhouses of the Cell and Their Role in Health
- Samah Akhter
- 18 minutes ago
- 6 min read
(World Mitochondrial Disease Awareness Week: September 15–21)
September 15–21 is World Mitochondrial Disease Awareness Week. In honor of this week, this article explains what mitochondria are, their genetics, the diseases associated with them, and why awareness is important.
What Are Mitochondria?
If you recall your biology classes, you may remember the phrase: “mitochondria are the powerhouses of the cell.” That is essentially their main function.
Our bodies are made of trillions of cells, the basic units of life. Think of cells like Lego pieces; by putting them together, you form a whole person. Inside each cell are different parts (organelles), each with its own role. One of the most important is the mitochondrion (plural: mitochondria).
Mitochondria act like tiny batteries, producing energy in the form of adenosine triphosphate (ATP). They generate about 90% of the energy in most cells. Without them, most cells cannot survive.
The number of mitochondria in each cell can vary depending on how much energy the cell needs. For example, muscle, liver, kidney, and brain cells contain especially high numbers of mitochondria because they require more energy.
Beyond producing ATP, mitochondria also help with:
Cell signaling (sending messages between cells)
Programmed cell death (apoptosis), which helps maintain tissue health
Calcium storage
Heat production
Structure of Mitochondria
Mitochondria are extremely small, usually between 0.5 and 3 micrometers, and are not visible under a microscope without staining. Each part contributes to its energy-producing efficiency:
Outer membrane: Allows small molecules to pass freely in and out of the mitochondrion.
Inner membrane: Where most ATP is created.
Cristae: Folds in the inner membrane that increase surface area, giving more room for chemical reactions.
Matrix: The fluid inside the inner membrane. It contains hundreds of proteins for ATP production, as well as the mitochondria’s own DNA (mtDNA).
Ribosomes: Use mtDNA to help produce proteins needed for energy metabolism.
Genetics of Mitochondria
Most DNA is found in the nucleus of a cell, but mitochondria also have their own DNA, called mitochondrial DNA (mtDNA).
mtDNA is circular and contains 37 genes.
Unlike nuclear DNA (inherited 50% from each parent), mtDNA is inherited only from the mother. This is because the egg provides the cytoplasm (jelly like substance floating in the cell), which contains the mother’s mitochondria, during fertilization. The father’s mtDNA is broken down and lost.
Like nuclear DNA, mtDNA serves as an instruction manual, but specifically for producing energy within the cell.
Mitochondrial Diseases
Mitochondrial diseases affect about 1 in 5,000 people. They occur when there are genetic changes (variants or mutations) in either mtDNA or nuclear DNA that disrupt mitochondrial pathways.
These changes can be:
Inherited from parents
De novo (new and spontaneous, without family history)
Because mitochondria fuel nearly every cell, these diseases can cause a wide variety of symptoms, often involving multiple organ systems.
Severity ranges from mild to life-threatening.
Age of onset varies, from infancy to adulthood. Generally, earlier onset leads to faster progression.
Even within the same family, people with the same mitochondrial condition may have different symptoms and severity.
Because muscle and nerve cells have especially high energy needs, muscular and neurological problems are common features of mitochondrial disorders. Other common symptoms associated and observed with mitochondrial diseases are:
Loss of muscle coordination, weakness, pain, and low muscle tone
Chronic fatigue
Problems with vision or hearing
Developmental delays or issues with cognitive development
Exercise intolerance
Heart, liver, or kidney disease
Gastrointestinal problems - diarrhea or constipation, unexplained vomiting, acid reflux, and/or swallowing difficulties
Neurological problems - dementia, seizures, migraines
Poor growth
Breathing problems
Fainting
Examples of mitochondrial diseases
Barth syndrome (nuclear DNA) - affects the breakdown of lipids (fatty compounds)
Chronic progressive external ophthalmoplegia (nuclear DNA and/or mtDNA) - weakness and an inability to move the eyes
Kearns-Sayre syndrome (mtDNA) - affects the retina, accompanied by heart problems, eyelid droop, mild skeletal muscle weakness, heart block, short stature, hearing loss, and diabetes.
Leigh syndrome (mtDNA) - gastrointestinal issues, loss of head control and motor skills, and seizures followed by generalized weakness and lack of muscle tone.
Mitochondrial DNA depletion syndromes (nuclear DNA) - muscle weakness, brain abnormalities, and liver disease
Pearson syndrome (mtDNA) - anemia and pancreatic issues
Neuropathy, ataxia, and retinitis pigmentosa (NARP) (mtDNA) - degeneration of the retina in the eye with resulting loss of vision, developmental delay, seizures, and dementia.
Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) (nuclear DNA) - eyelid droop, limb weakness, nerve damage, gastrointestinal problems.
Myoclonus epilepsy with ragged red fibers (MERRF) (mtDNA) - muscle jerks, seizures, ataxia, and muscle weakness, hearing problems, and short stature.
Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) (mtDNA) - seizures and/or dementia, build up of lactic acid in the body (lactic acidosis), and recurrent stroke-like episodes, can lead to progressive brain injury.
Diagnosis
The diagnostic approach involves a lot of evaluations. Since many organ systems are involved, the diagnosis timeline could be long and difficult to come to a conclusion in a single test. There is no single test or evaluation that would diagnose mitochondrial disease effectively. Some of the evaluations are:
An evaluation of medical and family history.
Exercise testing to monitor strength and exercise tolerance
Neurological and cognitive exams - tests of reflexes, vision, speech, and basic cognitive (thinking) skills.
Laboratory tests to look for diabetes, liver and kidney problems, and elevated lactic acid and pyruvate levels in the blood (or urine).
Lactic acid and pyruvate are two compounds involved in the ATP production cycle inside the mitochondria.
In mitochondrial disease, typically, the ratio of lactic acid to pyruvate is elevated, which indicates that the mitochondria are not efficiently using oxygen to produce energy.
Vision and hearing tests
Muscle biopsies (to analyze mitochondrial activity)
EKG (electrocardiogram) to check the heart for signs of arrhythmia (heart beat rhythm abnormalities) and cardiomyopathy (heart muscle weakness)
Diagnostic imaging, such as CT/MRI for brain abnormalities, or EEG if seizures are present
Genetic testing - can confirm a mitochondrial variant, but a negative test does not completely rule out disease (the variant may be undetectable or not yet identified).
Treatment
There are currently no cures or specific treatments for mitochondrial diseases. Generally, treatment is focused on managing symptoms and may include:
Physical, speech, and occupational therapy
Medications for seizures, cardiac issues, vitamins and supplements, or special diets.
Assistive devices for hearing loss, like hearing aids, cochlear implants, and regular monitoring for vision and hearing loss.
Support for respiratory issues
Cardiac evaluations for arrhythmias and cardiomyopathy
Management for gastrointestinal problems, diabetes, and/or kidney problems
Unique Properties of mtDNA
Multiple copies per cell: each cell has many mitochondria, and each mitochondrion has its own mtDNA.
Maternal inheritance: mtDNA is always inherited from the mother.
Homoplasmy vs. Heteroplasmy:
Homoplasmy: all mtDNA copies in a cell are identical (either typical or all containing a variant).
Heteroplasmy: a mixture of typical and variant mtDNA. The effects depend on the proportion of variant mtDNA, a “threshold effect.”\
The higher the number of mtDNA with pathogenic variants, the more likely the cell will be impacted in its biochemical functions, resulting in mitochondrial disease.
The ratios can differ in different cells in different parts of the bod,y and symptoms will more likely be seen in organs where the cells have a higher number of pathogenic variants containing mitochondria.
This explains why one person with mitochondrial disease may have mild symptoms while another family member with the same condition has severe symptoms.
In the image below, mutant means mtDNA with a pathogenic variant, and phenotype means physical expression of a trait.
Why Awareness Matters
Mitochondrial diseases are complex, underdiagnosed, and often misunderstood. Families frequently face a long diagnostic journey. Raising awareness:
Improves recognition of symptoms by healthcare providers
Supports earlier diagnosis and care
Encourages research into treatments
Strengthens patient and caregiver communities
References:
Mitochondria. (n.d.). Genome.gov. https://www.genome.gov/genetics-glossary/Mitochondria
Peck, P. (n.d.). What are Mitochondria. MRC Mitochondrial Biology Unit. https://www.mrc-mbu.cam.ac.uk/what-are-mitochondria
Newman, T. (2025, May 27). What are mitochondria? https://www.medicalnewstoday.com/articles/320875
Picard, M. (2025, August 26). Why Mitochondria Are More like a Motherboard Than the Powerhouse of the Cell. Scientific American. https://www.scientificamerican.com/article/why-mitochondria-are-more-like-a-motherboard-than-the-powerhouse-of-the-cell/
Mitochondrial DNA - Genetics - UZB website. (n.d.). Genetics. https://www.uzbrussel.be/en/web/genetics/mitochondrial-dna
Mitochondria and health. (2025, September 18). National Institutes of Health (NIH). https://www.nih.gov/news-events/nih-research-matters/mitochondria-health
Armstrong, B. (2023, June 12). All about mitochondria: Definition and disease. Genomics Education Programme. https://www.genomicseducation.hee.nhs.uk/blog/all-about-mitochondria-definition-and-disease/
Ng, Y. S., & Turnbull, D. M. (2015). Mitochondrial disease: genetics and management. Journal of Neurology, 263(1), 179–191. https://doi.org/10.1007/s00415-015-7884-3
The Kingsley Clinic. (2025, February 28). Understanding the Lactate-to-Pyruvate Ratio for Metabolic Health - The Kingsley Clinic. https://thekingsleyclinic.com/resources/understanding-the-lactate-to-pyruvate-ratio-for-metabolic-health/
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