Is MELAS Syndrome hereditary?

TL;DR: MELAS syndrome is a hereditary condition caused by mutations in mitochondrial DNA, meaning it is passed down exclusively from the mother to all of her children. Because it follows a mitochondrial inheritance pattern, the risk of transmission is high, though the severity of symptoms can vary significantly among family members due to a phenomenon called heteroplasmy.

Is MELAS syndrome considered a hereditary condition?

Yes, MELAS syndrome (Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-like episodes) is a hereditary condition. It is important to distinguish between "genetic" and "hereditary": while all hereditary diseases are genetic (caused by changes in DNA), not all genetic conditions are hereditary. MELAS syndrome is strictly hereditary because the disease-causing mutations reside in the mitochondrial DNA (mtDNA), which is inherited maternally. Unlike nuclear DNA, which we inherit from both parents, mitochondria are passed down only through the egg cell.

What is the inheritance pattern of MELAS syndrome?

MELAS syndrome follows a maternal (mitochondrial) inheritance pattern. This means that a woman who carries the mutation will pass it to all of her children, regardless of their biological sex. However, men who have MELAS syndrome do not pass the condition on to their children. A critical concept in this inheritance is "heteroplasmy," which refers to the presence of both mutated and healthy mitochondria within a single cell. The ratio of mutated to healthy mitochondria often determines the clinical severity of MELAS syndrome, which explains why family members may experience vastly different symptoms, ranging from mild muscle weakness to severe stroke-like episodes.

Are de novo (spontaneous) mutations common in MELAS syndrome?

While the majority of MELAS syndrome cases are inherited from a mother who may or may not show symptoms, de novo or spontaneous mutations can occur. These happen when the mutation arises for the first time in an individual due to an error during early embryonic development. However, these spontaneous cases are less common than inherited ones. Because MELAS syndrome is complex, genetic testing is essential to determine whether the mutation is familial or a new occurrence.

How is genetic testing and counseling utilized for MELAS syndrome?

Genetic testing for MELAS syndrome typically involves analyzing blood, muscle tissue, or sometimes urinary sediment to identify specific pathogenic variants, such as the common m.3243A>G mutation. Genetic counseling is strongly recommended for any family affected by MELAS syndrome for the following reasons:

• Risk Assessment: Counselors help interpret the likelihood of transmission based on the mother’s heteroplasmy levels.


• Reproductive Options: Families may discuss prenatal diagnosis or preimplantation genetic testing (PGT) to screen embryos for the mutation.


• Family Screening: Identifying the mutation allows for the early monitoring of asymptomatic relatives who may be at risk of developing MELAS syndrome later in life.


• Psychosocial Support: Connecting with the 80 members of the DiseaseMaps.org community provides invaluable peer support for navigating these complex genetic decisions.

Next steps

• Consult with a board-certified clinical geneticist or a metabolic specialist to discuss diagnostic testing and family screening.


• Request a referral to a genetic counselor who specializes in mitochondrial disorders to discuss reproductive risks and family planning.


• Join the DiseaseMaps.org community to connect with other families managing the daily realities of this condition.


• Keep a detailed family medical history, specifically noting maternal relatives with history of stroke, diabetes, or deafness.

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

References

• Orphanet: Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-like episodes (MELAS).


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


• OMIM (Online Mendelian Inheritance in Man): Mitochondrial Myopathy, Encephalopathy, Lactic Acidosis, and Stroke-like Episodes.


• United Mitochondrial Disease Foundation (UMDF): Information on mitochondrial inheritance patterns.