Mitochondrial encephalomyopathy lactic acidosis and stroke-like episodes

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]

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.

To find a medical professional who specializes in genetics, you can ask your doctor for a referral or you can search for one yourself. Online directories are provided by the American College of Medical Genetics and the National Society of Genetic Counselors. If you need additional help, contact a GARD Information Specialist. You can also learn more about genetic consultations from Genetics Home Reference.