Merck Manual

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Mitochondrial Disorders


Matt Demczko

, MD, Sidney Kimmel Medical College of Thomas Jefferson University

Last full review/revision Apr 2020| Content last modified Apr 2020
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Mitochondrial disorders are a group of hereditary metabolic disorders that occur when mitochondria do not function correctly in the body. Hereditary disorders occur when parents pass the defective genes that cause these disorders on to their children.

Mitochondria are tiny structures inside cells that provide the cells with energy. Mitochondria are present in every cell except red blood cells. Unlike other structures inside cells, mitochondria have some of their own genetic material that is inherited only from the mother. Other genetic material for the mitochondria is in the cell nucleus with the rest of the cell's genetic material, and children with a disorder must inherit an abnormality from each parent.

Mitochondrial disorders cause mitochondria to stop working properly, so that less and less energy is generated within the cells. This may lead to cell injury or even cell death and body systems will not function properly.

Mitochondria supply energy to many organs in the body. Some of these organs, such as the brain, nerves, muscles, and retinas, require more energy than others do. These high-energy organs are particularly susceptible to the problems caused by mitochondrial disorders. Depending on which cells are affected, problems include the following:

When mitochondria do not function properly, a waste product called lactic acid can build up in the bloodstream (called lactic acidosis). This buildup of lactic acid may help distinguish a mitochondrial disorder from other metabolic diseases. The following are examples of mitochondrial disorders.

Leber hereditary optic neuropathy (LHON)

Leber hereditary optic neuropathy can cause progressive vision loss in both eyes. Some people also have heart problems or muscle symptoms (such as involuntary muscle contractions, muscle weakness, or muscle spasms). The disorder is more common among men, and symptoms often begin when people are in their 20s or 30s.

No treatments are available. However, limiting the consumption of alcohol, which may affect the mitochondria, and not using tobacco products may slow the progression of symptoms.

Leigh syndrome

Infants who have Leigh syndrome may have trouble feeding, poor head control, and delayed development. They may also have vomiting, irritability, continuous crying, and seizures that worsen during times of illness. This disorder begins in infants between the ages of 3 months and 2 years. Rarely, it occurs in adolescents and adults. As the disorder progresses, symptoms may also include generalized weakness, lack of muscle tone, and episodes of lactic acidosis, which can lead to breathing and kidney problems.

There are no known treatments for Leigh syndrome. However, a very small number of children have a specific kind of Leigh syndrome that benefits from supplements of thiamin (vitamin B1).

Mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes (MELAS)

Children who have MELAS may have muscle weakness and pain, recurring headaches, hearing loss, loss of appetite, vomiting, and seizures. Most affected people have stroke-like episodes beginning before age 40. These episodes often cause temporary muscle weakness on one side of the body, altered consciousness, vision abnormalities, seizures, and severe headaches resembling migraines. Repeated stroke-like episodes can progressively damage the brain, leading to vision loss, problems with movement, and dementia. Symptoms of MELAS most often appear in late childhood and adolescence but can begin at any age.

No specific treatment is available for MELAS, but various drugs and treatments are used to manage symptoms.

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