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Genetic and Rare Diseases Information Center (GARD)

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Mitochondrial encephalomyopathy lactic acidosis and stroke-like episodes


Other Names for this Disease

  • MELAS
  • MELAS syndrome
See Disclaimer regarding information on this site. Some links on this page may take you to organizations outside of the National Institutes of Health.

Your Question

My brother was diagnosed with MELAS several years ago. His wife informed me that his doctor said that all 3 of us children inherited the gene from our mother. His diagnosis was confirmed after viewing our mother's autopsy reports. How probable is it that myself or our other brother will be affected by this disease?

Our Answer

We have identified the following information that we hope you find helpful. If you still have questions, please contact us.

How is mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) inherited?

MELAS is caused by mutations in mitochondrial DNA (mtDNA) and is therefore transmitted by maternal inheritance (also called mitochondrial inheritance).[1] This type of inheritance applies to all conditions caused by genes in mtDNA. Mitochondria are structures in each cell that turn molecules into energy, and each contain a small amount of DNA. Only egg cells (not sperm cells) contribute mitochondria to offspring, so only females can pass on mitochondrial mutations to their children.[2] Conditions resulting from mutations in mtDNA can appear in every generation of a family and can affect both males and females. In most cases, people with MELAS inherit an altered mitochondrial gene from their mother. Less commonly, the condition results from a new mutation in a mitochondrial gene and occurs in an individual with no history of MELAS in the family.[2]
Last updated: 12/4/2013

What is the chance that a sibling of an individual with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) will be affected?

The risk to the siblings of an individual affected with MELAS depends on the genetic status of their mother. If their mother has the mtDNA mutation, all of the siblings of the affected individual will inherit the disease-causing mtDNA mutation; however, the siblings may or may not have symptoms. One study reported that women with higher levels of the mutated mtDNA in their blood have a greater likelihood of having affected offspring (i.e. children with symptoms of the condition).[1]

Unfortunately, it is not possible to predict whether an individual with an mtDNA mutation will have specific symptoms. The possible effects of an mtDNA mutation depend on a combination of factors, including the severity of the mutation, the percentage of mitochondria that have the mutation, and the organs and tissues in which the mutated mitochondria are located. Different family members often inherit different percentages of mutated mtDNA and therefore can have a wide range of clinical symptoms. Test results of at-risk family members who don't currently have symptoms are very hard to interpret.[1]

Individuals concerned about specific risks to themselves or family members should speak with a genetics professional.
Last updated: 12/4/2013

How can I find a genetics professional in my area?

Genetics clinics are a source of information for individuals and families regarding genetic conditions, treatment, inheritance, and genetic risks to other family members. More information about genetic consultations is available from Genetics Home Reference. To find a genetics clinic, we recommend that you contact your primary healthcare provider for a referral.

The following online resources can help you find a genetics professional in your community:
Last updated: 6/5/2014

References
Other Names for this Disease
  • MELAS
  • MELAS syndrome
See Disclaimer regarding information on this site. Some links on this page may take you to organizations outside of the National Institutes of Health.