Which are the causes of MELAS Syndrome?

TL;DR: MELAS syndrome is a rare, multisystem genetic disorder caused by mutations in mitochondrial DNA (mtDNA), which impairs the body’s ability to produce energy. It is primarily inherited maternally, meaning it is passed from a mother to her children through the mitochondria in the egg cell.

What causes MELAS syndrome at the genetic level?

The root cause of MELAS syndrome (Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-like episodes) lies in the mitochondria—the "power plants" of our cells. While most of our DNA is stored in the cell nucleus, mitochondria contain their own small, circular DNA. In MELAS syndrome, specific point mutations in the mitochondrial DNA interfere with the cell's ability to create proteins necessary for the oxidative phosphorylation process, which is how we generate chemical energy (ATP). The most common mutation associated with MELAS syndrome is the m.3243A>G mutation in the MT-TL1 gene.

How is MELAS syndrome inherited?

MELAS syndrome follows a unique pattern of inheritance known as maternal (or mitochondrial) inheritance. Because mitochondria are inherited exclusively from the mother’s egg, a woman with the mutation can pass it to all of her children, whereas an affected man generally does not pass the condition to his offspring. However, the severity of MELAS syndrome can vary significantly within the same family due to a concept called "heteroplasmy." This means that each cell contains a mixture of both healthy and mutated mitochondria; the ratio of mutated to healthy mitochondria often determines the severity of the symptoms.

Are there environmental triggers or risk factors for MELAS syndrome?

While the primary cause of MELAS syndrome is genetic, environmental factors can act as "stressors" that exacerbate the disease process. Because the body is struggling to produce enough energy, high-stress situations can trigger the signature "stroke-like episodes." Known triggers include:

• Infections: Viral or bacterial illnesses place an increased energy demand on the body, which can destabilize cellular function.


• Physical Exertion: Intense physical stress may exceed the limited energy reserves of the mitochondria.


• Certain Medications: Some drugs, such as valproic acid or specific antibiotics, are known to be toxic to mitochondria and can worsen the condition.


• Metabolic Stress: Fasting or severe dehydration can disrupt the already fragile metabolic balance in patients with MELAS syndrome.

Is the cause of MELAS syndrome fully understood?

While we know the specific genetic mutations that define MELAS syndrome, researchers are still working to understand why the disease manifests so differently between individuals. We do not yet fully understand why some people with the m.3243A>G mutation remain asymptomatic while others experience severe neurological decline. Current research is focusing on "mitochondrial replacement therapy" and pharmacological interventions aimed at "bypassing" the energy deficit, as well as studying how nuclear-encoded genes might modify the expression of the mitochondrial mutations.

Next steps

• Consult a metabolic specialist or a clinical geneticist to discuss genetic testing and family planning options.


• Connect with the 80 members of the DiseaseMaps.org community who are living with MELAS syndrome to share experiences and coping strategies.


• Maintain a detailed medical record, including a list of any medications that have triggered symptoms, to share with your healthcare team.


• Regularly check clinical trial databases like ClinicalTrials.gov for emerging therapies targeting mitochondrial disorders.

Medical disclaimer: This information is for educational purposes only and does not constitute medical advice, diagnosis, or treatment; always seek the advice of your physician or other qualified health provider with any questions regarding a medical condition.

References

• NIH Genetic and Rare Diseases Information Center (GARD): MELAS syndrome.


• Orphanet: Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes.


• OMIM (Online Mendelian Inheritance in Man): Mitochondrial DNA-encoded tRNA leucine 1 (MT-TL1) mutation.


• United Mitochondrial Disease Foundation (UMDF): Information on mitochondrial disease genetics.