Mitochondrial Disease | Symptoms & Causes

What are the symptoms of mitochondrial disease?

Because mitochondria are in every cell of the body, mitochondrial disorders can affect many different body systems and cause a wide variety of symptoms in different combinations. This can make them challenging to diagnose.

The parts of the body that tend to be most affected are those that need the most energy, such as the heart, brain, muscles and gastrointestinal tract. Symptoms can range from fatigue and exercise intolerance to hearing loss, seizures, strokes, heart failure, diabetes and kidney failure. A large majority but not all children with mitochondrial disorders have developmental delay.

Depending on the severity of the disorder, symptoms can appear at birth or they may not appear until adulthood. In some children, mitochondrial disease progresses quickly and can be severe. In others, it can be stable and well-managed for many years. Sometimes symptoms begin suddenly, triggered by another illness.

What causes mitochondrial disease

Mitochondria are the “power plants” of all the cells in the human body, producing the energy our bodies need to function. They are also involved in metabolism, helping our cells build, break down and recycle compounds they need.

In mitochondrial disorders, the mitochondria’s ability to do these jobs is impaired because of a genetic mutation — a “mistake” in the DNA. We all have two types of DNA in our bodies. The nuclear DNA (usually just called “DNA”) is found in the cell's nucleus and is inherited from both our mother and father. Mitochondria also have DNA, inherited from mothers. Because both types of DNA are responsible for the structure and function of the mitochondria, mutations in either can cause mitochondrial disorders. Mutations can be inherited from parents or can happen for the first time in a child (so-called de novo mutations).

Inherited mutations in the mitochondrial DNA come from the mother. Mutations in nuclear DNA usually are recessive, meaning that one copy of the mutation comes from each parent. In this case, the parents are just carriers and do not have mitochondrial disease themselves. This also explains why some people with a mitochondrial disorder have a family history of the disorder, while others are the only one in their family to be affected.

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