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Mitochondria (Figure 1.) are the powerhouse of the cell, providing the energy a cell needs to function by converting the energy from food into a useable form for cellular function.1


Figure 1. This image was obtained from The National Human Genome Research Institute “Talking Glossary of Genetic Terms.” The double membrane of the mitochondria can be seen, as well as its own genetic material.

Mitochondria have two membranes and generate their energy in the form of adenosine triphosphate (ATP) (Figure 2). The inner membrane of the mitochondrion is home to the electron transport chain (ETC), a chain made out of complexes that transfer electrons, and produce ATP. Mitochondria contain their own special genetic material (DNA), as mitochondrial DNA (mtDNA) (Figure 1).

Changes or mutations in mtDNA can result in mitochondrial dysfunction leading to mitochondrial diseases.


Figure 2. This was obtained from https://www.luminultra.com/what-is-atp-and-what-does-it-do/ and shows the structure of the high energy molecule, ATP that is generated by the mitochondria to provide energy to other cells.

Mitochondrial diseases arise when dysfunctional mitochondria are unable to generate enough ATP to meet the energy demands of several organs, especially those that require a lot of energy. This includes the nervous system, skeletal and heart muscles, kidneys, liver, and endocrine systems.

In a healthy person, mtDNA molecules are identical for the most part. But in people with diseases caused by mtDNA mutations, both normal and mutant mtDNA molecules typically can exist in a single cell, resulting in differing degrees of disease severity is often depending on the amount of mutant mtDNA in cells, which is in turn determined by genetic events when that person’s mother was still an embryo!2

Like most genetic material, mtDNA can be passed on and is one of the most frequent maternally inherited mitochondrial disorders. A recent study published in January of 2019 suggests that mitochondrial DNA may not exclusively come from the mother, which can explain cases where the mother does not have a mutation, but the children do possess a mutation.

Figure 3. MELAS is an acronym for Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-Like Symptoms. This image can be found at
https://www.allacronyms.com/MELAS/mitochondrial_encephalomyopathy,_lactic_acidosis_and_stroke-like_episodes

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) is a condition that affects many of the body’s systems such as the brain and nervous system (encephalo-) and muscles (myopathy). Defining features of this disease include the appearance of ragged red fibers (RRFs) in skeletal muscle, short stature, seizures, and hemiparesis (partial weakness on one side of the body), hemianopia (blindness in half the field of vision), or blindness. The diagnosis is considered confirmed if there are also at least two of the following criteria: 1) normal early psychomotor development, 2) recurrent headaches, and 3) recurrent vomiting episodes.3