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Understanding MELAS: What it is and Why it Happens

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MELAS is a rare, maternally inherited mitochondrial disease that prevents cells from producing enough energy. It is primarily caused by the m.3243A>G mutation, leading to an energy deficit that triggers lactic acidosis, muscle weakness, and stroke-like episodes in the brain.

Key Takeaways

  • • MELAS is a mitochondrial disorder that prevents cells from producing enough energy for the brain, muscles, and nervous system.
  • • The condition is most commonly caused by the m.3243A>G mutation in the MT-TL1 gene.
  • • MELAS is maternally inherited, meaning the genetic mutation is passed down exclusively from the mother.
  • • Symptom severity is determined by heteroplasmy, which is the ratio of mutated to healthy mitochondrial DNA in your tissues.
  • • Stroke-like episodes in MELAS are caused by brain energy crises rather than typical blood clots.

Receiving a diagnosis of MELAS—or even suspecting it—is terrifying. It is completely normal to feel overwhelmed, confused, and anxious about what this means for you or your child. You are likely facing a steep learning curve filled with complex medical jargon. This guide is designed to translate that medical data into a clear, empowering strategy so you can advocate for the best possible care.

MELAS is a rare genetic condition that primarily affects the brain, muscles, and nervous system. The name is an acronym that describes its most common features: Mitochondrial Encephalomyopathy (brain and muscle disease), Lactic Acidosis (buildup of lactic acid), and Stroke-like episodes [1][2].

While the name sounds overwhelming, at its core, MELAS is a challenge of energy production [3]. It occurs when the “power plants” of your cells, called mitochondria, cannot produce enough fuel for the body to function normally [4].

The Energy Crisis: Why MELAS Happens

Most cells in your body contain hundreds of mitochondria. Their job is to take the oxygen we breathe and the food we eat and turn them into a form of energy called ATP [5].

In about 80% of people with MELAS, a specific “typo” occurs in the mitochondrial DNA at a location known as m.3243A>G [6][4]. This mutation disrupts the MT-TL1 gene, which is responsible for building the machinery that makes energy [3].

When this machinery is broken:

  • Energy Deficit: The cells cannot create enough ATP to power high-energy organs like the brain and heart [4][7].
  • Lactic Acid Buildup: To compensate for the lack of mitochondrial energy, the body switches to a less efficient backup system called anaerobic glycolysis [5]. A byproduct of this backup system is lactic acid. When too much lactic acid builds up in the blood or brain fluid, it is called lactic acidosis [5][8].
  • Stroke-Like Episodes: These are not typical strokes caused by blood clots. Instead, they are thought to be “energy crises” in the brain where the demand for power exceeds the supply, sometimes triggered by the narrowing of small blood vessels [1][9].

Understanding Heteroplasmy: Why Severity Varies

You may wonder why one person with the MELAS mutation has mild symptoms while another is severely affected. The answer lies in a concept called heteroplasmy [7].

Unlike the DNA in your cell’s nucleus (which is the same in every cell), you have many copies of mitochondrial DNA. Heteroplasmy is the percentage of mutated DNA versus healthy DNA within a cell or tissue [7][10].

  • If a person has a low percentage of mutated DNA, they may have no symptoms or only mild ones, such as hearing loss or diabetes [7][11].
  • If they have a high percentage of mutated DNA in critical organs like the brain or muscles, the symptoms are typically more severe [12][13].

Because mitochondria divide and distribute randomly as cells grow, different parts of the body can have different levels of the mutation [10][14]. This is why doctors may sometimes need to test urine or muscle if a blood test isn’t clear [15][16].

Inheritance: The Maternal Path and Your Family

MELAS is a maternally inherited condition [17]. This means the mutation is passed down from the mother. While both men and women can have MELAS, only women can pass the mutation to their children [6][17]. This is because, at conception, the embryo receives all of its mitochondria from the mother’s egg, not the father’s sperm [18].

Because of this inheritance pattern, if you or your child are diagnosed, it is crucial to seek genetic counseling for your extended family. Maternal relatives (such as siblings, maternal aunts/uncles, and a mother’s other children) may also carry the mutation, even if they currently have no symptoms or only mild issues like diabetes. A genetic counselor can help guide testing for family members.

Understanding that MELAS is a biological energy failure—rather than a typical “illness”—can help you and your medical team focus on managing the Symptoms and Stroke-like Episodes that arise.

Frequently Asked Questions

What causes MELAS?
MELAS is caused by a genetic mutation that damages your mitochondria, the power plants of your cells. In about 80% of cases, it is caused by a specific mutation called m.3243A>G, which stops cells from making enough energy to power high-demand organs like the brain and heart.
How is MELAS inherited?
MELAS is a maternally inherited condition, which means the genetic mutation is passed down from the mother. While both men and women can have the condition, only women can pass the mutated mitochondrial DNA to their children.
Why do symptoms of MELAS vary so much from person to person?
The severity of MELAS depends on a concept called heteroplasmy, which is the percentage of mutated DNA versus healthy DNA in your cells. People with a high percentage of mutated DNA in their brain or muscles usually have more severe symptoms, while those with a lower percentage may only experience mild issues like hearing loss.
What are the stroke-like episodes in MELAS?
Unlike regular strokes caused by blood clots, stroke-like episodes in MELAS are considered energy crises in the brain. They occur when the brain's demand for power exceeds the limited energy supply that the damaged mitochondria can provide.
Why does my doctor need to monitor my lactate levels?
Because your mitochondria cannot produce energy efficiently, your body uses a backup system that creates lactic acid as a byproduct. Monitoring lactate levels helps your doctor see how well your body is producing energy and if a dangerous buildup is occurring.

Questions for Your Doctor

  • • What is my (or my child’s) specific heteroplasmy level, and which tissue was tested?
  • • How does the m.3243A>G mutation specifically explain the symptoms I am seeing?
  • • Are there other family members who should be tested based on the maternal inheritance of this condition?
  • • How often should we monitor lactate levels, and what do those numbers tell us about energy production?

Questions for You

  • • Have any of my maternal relatives (mother, aunts, uncles, siblings) experienced hearing loss, diabetes, or muscle weakness?
  • • What specific symptoms or 'episodes' have I noticed that seem to happen during times of physical stress or illness?
  • • On a daily basis, how would I describe my (or my child's) energy levels and muscle strength?

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References

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    MELAS syndrome: Clinical manifestations, pathogenesis, and treatment options.

    El-Hattab AW, Adesina AM, Jones J, Scaglia F

    Molecular genetics and metabolism 2015; (116(1-2)):4-12.

    PMID: 26095523
  2. 2

    Acute Management of Neurological Events in Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-Like Episodes (MELAS) Syndrome: A Case Report.

    Aladashvili Z, Rodriguez TB, Izquierdo-Pretel G

    Cureus 2025; (17(5)):e83959 doi:10.7759/cureus.83959.

    PMID: 40502899
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    Clinical Characteristics of Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-Like Episodes.

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    Life (Basel, Switzerland) 2021; (11(11)) doi:10.3390/life11111111.

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    The addition of ketone bodies alleviates mitochondrial dysfunction by restoring complex I assembly in a MELAS cellular model.

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    Biochimica et biophysica acta. Molecular basis of disease 2017; (1863(1)):284-291 doi:10.1016/j.bbadis.2016.10.028.

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    Mitochondrial cytopathy with common MELAS mutation presenting as multiple system atrophy mimic.

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    Circulating markers of NADH-reductive stress correlate with mitochondrial disease severity.

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    The Journal of clinical investigation 2021; (131(2)).

    PMID: 33463549
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    Arginine and citrulline for the treatment of MELAS syndrome.

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    Journal of inborn errors of metabolism and screening 2017; (5()) doi:10.1177/2326409817697399.

    PMID: 28736735
  10. 10

    Heteroplasmy and phenotype spectrum of the mitochondrial tRNALeu (UUR) gene m.3243A>G mutation in seven Han Chinese families.

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    Journal of the neurological sciences 2020; (408()):116562 doi:10.1016/j.jns.2019.116562.

    PMID: 31722256
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    Retinal multimodal-imaging and functional tests in a mitochondrial disease with focal and segmental glomerulosclerosis.

    Liu XH, Shen X, Zhong YS

    International journal of ophthalmology 2025; (18(9)):1770-1776 doi:10.18240/ijo.2025.09.19.

    PMID: 40881443
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    Intramyocellular lipid excess in the mitochondrial disorder MELAS: MRS determination at 7T.

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    Neurology. Genetics 2017; (3(3)):e160 doi:10.1212/NXG.0000000000000160.

    PMID: 28589178
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    Outcomes misaligned in mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS): implications for trial design.

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  14. 14

    MELAS Syndrome and Kidney Disease Without Fanconi Syndrome or Proteinuria: A Case Report.

    Rudnicki M, Mayr JA, Zschocke J, et al.

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  15. 15

    Molecular and neurological features of MELAS syndrome in paediatric patients: A case series and review of the literature.

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    Case report: Late-onset MELAS syndrome with mtDNA 5783G>A mutation diagnosed by urinary sediment genetic testing.

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    Haemorrhagic Transformation of a MELAS Stroke-Like Lesion.

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  18. 18

    Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes with coexisting nemaline myopathy: a case report.

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This page provides educational information about the genetics and biological causes of MELAS. It is not a substitute for professional medical advice, diagnosis, or genetic counseling.

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